Drought-resistant grass to spur milk production

By Baraka Rateng’

Struggling East African dairy farmers could benefit from new varieties of high-quality, drought-resistant forage grass known as Brachiaria that boosts milk production by 40 per cent, a report says.

The forage grass could enable farmers to increase their incomes, according to experts at the Colombia-headquartered International Center for Tropical Agriculture (CIAT) – a CGIAR Research Center.

Steven Prager, a co-author of the report —  which was published last month — and a senior scientist in integrated modelling at the CIAT, says the report  was based on many years of forage research in Latin America and the Caribbean, and recent field trials in Kenya and Rwanda from 2011 to 2016.

According to Prager, the study demonstrates the high potential for improved forages in East Africa and high payoff for investment in improved forages.

“The results are based on multiple scenarios of an economic surplus model with inputs derived from a combination of databases, feedback from subject matter experts and a literature review,” he explains, adding that the economic analysis was carried out at CIAT headquarters with the support of tropical forage experts in East Africa.

Drought resistant grass
“The objective of this study was to understand the potential payoff for investment in action to improve dissemination and use of improved forages,” Prager tells SciDev.Net.

“The objective of this study was to understand the potential payoff for investment in action to improve dissemination and use of improved forages.”

Steven Prager, International Center for Tropical Agriculture (CIAT)

One of the big unknowns in the development and implementation of agricultural technology, according to Prager, is how many potential users are required to make it worthwhile to invest in the development and designation of different technologies.

Solomon Mwendia, a co-author of the report and forage agronomist at CIAT, Kenya, says the Brachiaria grass is climate-friendly and has high crude protein and less fiber, which leads to better use and digestion by cattle, in turn leading to less methane gas produced for each unit of livestock product such as milk or meat. Methane is one of the gases associated with global warming.

“This grass is relatively drought-tolerant compared to the Napier or elephant grass commonly used in East Africa. In addition, the grass can easily be conserved as hay for utilisation during forages scarcity or for sale,” Mwendia adds.

Smallholder dairy farming is important in East Africa for household nutrition and income. In Kenya, for instance, Mwendia says that milk production increased by 150 per cent between 2004 and 2012, from 197.3 million litres to 497.9 million litres.


East Africa cattle density 


The grass is native to Africa, according to Mwendia. It can grow in areas with up to 3,000 millimetres of rainfall and also withstand dry seasons of three to six months during which the leaf may remain green while other tropical species die. These conditions exist in other regions outside eastern Africa such as in Democratic Republic of Congo, Malawi, Zambia and Zimbabwe.

Sita Ghimire, a senior scientist at the Biosciences eastern and central Africa (BecA) Hub, who leads a research programme that focuses on Brachiaria, says 40 per cent increase in milk production is achievable in East Africa after feeding livestock with Brachiaria.


Livestock production in East Africa 


“Forage has been always a major challenge in livestock production in East Africa. It is mainly because of declining pastureland, frequent and prolonged drought and not many farmers conserve forage for dry season,” Ghimire says.

The major challenges for adoption of Brachiaria technology in East Africa are limited availability of seeds or  vegetative materials, lack of standardised agronomic practices for different production environments and lack of varieties that are well adapted to East African environment, Ghimire explains, citing other challenges such as pest and diseases, and low funding forage research and development.

This piece was produced by SciDev.Net’s Sub-Saharan Africa English desk.

References

Carlos González and others Improved forages and milk production in East Africa. A case study in the series: Economic foresight for understanding the role of investments in agriculture for the global food system (October 2016, Internacional de Agricultura Tropical [CIAT])

 

This article was originally published on SciDev.Net. Read the original article.

Genome editing: an introduction to CRISPR/Cas9

Damiano Martignago

Dr Damiano Martignago, Rothamsted Research

This week’s blog post was written by Dr Damiano Martignago, a genome editing specialist at Rothamsted Research.

 

Genome editing technologies comprise a diverse set of molecular tools that allow the targeted modification of a DNA sequence within a genome. Unlike “traditional” breeding, genome editing does not rely on random DNA recombination; instead it allows the precise targeting of specific DNA sequences of interest. Genome editing approaches induce a double strand break (DSB) of the DNA molecule at specific sites, activating the cell’s DNA repair system. This process could be either error-prone, thus used by scientists to deactivate “undesired” genes, or error-free, enabling target DNA sequences to be “re-written” or the insertion of DNA fragments in a specific genomic position.

The most promising among the genome editing technologies, CRISPR/Cas9, was chosen as Science’s 2015 Breakthrough of the Year. Cas9 is an enzyme able to target a specific position of a genome thanks to a small RNA molecule called guide RNA (gRNA). gRNAs are easy to design and can be delivered to cells along with the gene encoding Cas9, or as a pre-assembled Cas9-gRNA protein-RNA complex. Once inside the cell, Cas9 cuts the target DNA sequence homologous to the gRNAs, producing DSBs.

CRISPR/Cas9

The guide RNA (sgRNA) directs Cas9 to a specific region of the genome, where it induces a double-strand break in the DNA. On the left, the break is repaired by non-homologous-end joining, which can result in insertion/deletion (indel) mutations. On the right, the homologous-directed recombination pathway creates precise changes using a supplied template DNA. Credit: Ran et al. (2013). Nature Protocols.

 

Genome editing in crops

Together with the increased data availability on crop genomes, genome editing techniques such as CRISPR are allowing scientists to carry out ambitious research on crop plants directly, building on the knowledge obtained during decades of investigation in model plants.

The concept of CRISPR was first tested in crops by generating cultivars that are resistant to herbicides, as this is an easy trait to screen for and identify. One of the first genome-edited crops, a herbicide-resistant oilseed rape produced by Cibus, has already been grown and harvested in the USA in 2015.

Wheat powdery mildew

Researchers used CRISPR to engineer a wheat variety resistant to powdery mildew (shown here), a major disease of this crop. Image credit: NY State IPM Program. Used under license: CC BY 2.0.

 

Using CRISPR, scientists from the Chinese Academy of Sciences produced a wheat variety resistant to powdery mildew, one of the major diseases in wheat. Similarly, another Chinese research group exploited CRISPR to produce a rice line with enhanced rice blast resistance that will help to reduce the amount of fungicides used in rice farming. CRISPR/Cas9 has also been already applied to maize, tomato, potato, orange, lettuce, soybean and other legumes.

Genome editing could also revolutionize the management of viral plant disease. The CRISPR/Cas9 system was originally discovered in bacteria, where it provided them with molecular immunity against viruses, but it can also be moved into plants. Scientists can transform plants to produce the Cas9 and gRNAs that target viral DNA, reducing virus accumulation; alternatively, they can suppress those plant genes that are hijacked by the virus to mediate its own diffusion in the plants. Since most plants are defenseless against viruses and there are no chemical controls available for plant viruses, the main method to stop the spread of these diseases is still the destruction of the infected plant. For the first time in history, scientists have an effective weapon to fight back against plant viruses.

Cassava brown streak disease

The cassava brown streak disease virus can destroy cassava crops, threatening the food security of the 300 million people who rely on this crop in Africa. Image credit: Katie Tomlinson (for more on this topic, read her blog here).

 

Genome editing will be particularly useful in the genetic improvement of many crops that are propagated mainly by vegetative reproduction, and so very difficult to improve by traditional breeding methods involving crossing (e.g. cassava, banana, grape, potato). For example, using TALENs, scientists from Cellectis edited a potato line to minimize the accumulation of reducing sugars that may be converted into acrylamide (a possible carcinogen) during cooking.

 

Concerns about off-targets

One of the hypothesized risks of using CRISPR/Cas9 is the potential targeting of undesired DNA regions, called off-targets. It is possible to limit the potential for off-targets by designing very specific gRNAs, and all of the work published so far either did not detect any off-targets or, if detected, they occurred at a very low frequency. The number of off-target mutations produced by CRISPR/Cas9 is therefore minimal, especially if compared with the widely accepted random mutagenesis of crops used in plant breeding since the 1950s.

 

GM or not-GM

Genome editing is interesting from a regulatory point of view too. After obtaining the desired heritable mutation using CRISPR/Cas9, it is possible to remove the CRISPR/Cas9 integrated vectors from the genome using simple genetic segregation, leaving no trace of the genome modification other than the mutation itself. This means that some countries (including the USA, Canada, and Argentina) consider the products of genome editing on a case-by-case basis, ruling that a crop is non-GM when it contains gene combinations that could have been obtained through crossing or random mutation. Many other countries are yet to issue an official statement on CRISPR, however.

Recently, scientists showed that is possible to edit the genome of plants without adding any foreign DNA and without the need for bacteria- or virus-mediated plant transformation. Instead, a pre-assembled Cas9-gRNA ribonucleoprotein (RNP) is delivered to plant cells in vitro, which can edit the desired region of the genome before being rapidly degraded by the plant endogenous proteases and nucleases. This non-GM approach can also reduce the potential of off-target editing, because of the minimal time that the RNP is present inside the cell before being degraded. RNP-based genome editing has been already applied to tobacco plants, rice, and lettuce, as well as very recently to maize.

In conclusion, genome editing techniques, and CRISPR/Cas9 in particular, offers scientists and plant breeders a flexible and relatively easy approach to accelerate breeding practices in a wide variety of crop species, providing another tool that we can use to improve food security in the future.
For more on CRISPR, check out this recent TED Talk from Ellen Jorgensen:


About the author

Dr Damiano Martignago is a plant molecular biologist who graduated from Padua University, Italy, with a degree in Food Biotechnology in 2009. He obtained his PhD in Biology at Roma Tre University in 2014. His experience with CRISPR/Cas9 began in the lab of Prof. Fabio Fornara (University of Milan), where he used CRISPR/Cas9 to target photoperiod genes of interest in rice and generate mutants that were not previously available. He recently moved to Rothamsted Research, UK, where he works as Genome Editing Specialist, transferring CRISPR/Cas9 technology to hexaploid bread wheat with the aim of improving the efficiency of genome editing in this crop. He is actively involved with AIRIcerca (International Association of Italian Scientists), disseminating and promoting scientific news.

Does Australia hold the key to food security?

This article is reposted from the Devex blog with kind permission from the author, Lisa Cornish.

CIAT research

Plant samples in the genebank at the International Center for Tropical Agriculture’s Genetic Resources Unit, at the institution’s headquarters in Colombia. Credit: Neil Palmer / CIAT. Used under license: CC BY-SA 2.0.

It was too dry in the Australian region of Wimmera to produce crops last summer. This year, floods are set to wipe out yields again. Like a number of other regions across the planet, climate change is starting to be felt.

“It’s like this every year somewhere,” said Sally Norton, head of the Australian Grains Genebank, which stores diverse genetic material for plant breeding and research.

For Norton and many of her colleagues in agricultural genetics, the picture is increasingly clear: The variety of crops used today are not able to withstand the changing conditions and changes expected in the future.

Australia’s biodiversity may offer some help, according to discussions at the recent International Genebank Managers Annual General Meeting held in Horsham, Victoria. The gathering, which brings together 11 countries, focused on how to better conserve seeds, build databases to manage collections, boost capacity across the world and fill gaps in genebanks.

Researchers are particularly interested in crop wilds, “the ancestors of our domesticated crops,” Marie Haga, executive director of the The Crop Trust, explained to Devex. Australia is one of the richest sources of these seeds. “It’s like the wolf being the ancestor to our domesticated dogs. Crop wild relatives have traits that we have lost in the domestication process — they might need less water, might live in unfriendly conditions, may be resistant to pests and diseases.”

As climate change continues to batter agricultural yields, crop wild relatives could provide resilience. The seeds give breeders and farmers new options of plant varieties with traits to withstand a variety of conditions based on the harsh climates they are found — drought, fire, flood, poor soil, high salinity.

For Haga, crop wild relatives are a solution for food security. “The challenge is that many of the varieties widely used in modern agriculture are very vulnerable, because we have been breeding on the same line and they are adapted to very specific environment,” Haga said. Varieties that flourish today, she said, could wither as the climate fluctuates.

“Utilization of the natural diversity of crops is key to the future,” she said. “The climate is rapidly changing and we need to feed a growing population with more nutritious food. It is very hard to see how we can do this unless we go back to the building blocks of agriculture.”

Norton agreed: “Crop wild relatives have an amazing adaptability to changing conditions,” she told Devex. “When we talk about food security, we are talking about getting varieties in farm paddocks that have greater resilience to extreme conditions. It may not be the highest yield, but you are going to get something from this crop.”

Why have they been overlooked?

Crop wild relatives have so far been underutilized in the research and breeding process of crops.

“We have this fabulous natural diversity out there including 125,000 varieties of wheat and 200,000 varieties of rice.” Haga said. “We have not at all unlocked the potential of these crops.”

One reason is a dearth of research. “Adapting Agriculture to Climate Change: Collecting, Protecting and Preparing Crop Wild Relatives,” a 10-year project led by Haga to ensure long-term conservation of crop wild relatives, conducted a global survey of distribution and conservation and found that of 1,076 known wild relatives for 81 crops, more than 95 percent are insufficiently represented in genebanks and 29 percent are completely missing. They are missing purely due to the fact that they have yet to be collected.

“Genebank managers are generally open to include crop wild relatives in their collections.” Haga said. “It’s just quite simply that not enough work has been done in this area and the full potential is yet to be realized,” she said.

At the moment, seeds are being collected in 25 countries around the world as part of the crop wild relative project, but it is Australia that has been identified as one of the richest sources for crop wild relatives in the world. Because of the continent’s low population density and vast, undisturbed natural environment, a wide variety of species have been conserved, said Norton.

Australia holds significant diversity of wild relatives of rice, sorghum, pigeon pea, banana, sweet potato and eggplant currently missing from global collections, according to research by the Australian Seed Bank Partnership. Forty species have been prioritized for collection with high hopes that they will enable crops to withstand the harsh environmental conditions in which Australian species are found.

There are still many areas of Australia yet to be surveyed, and the full extent of its agricultural riches may yet to be tapped.

Australian researchers will play an important role in pre-breeding local species of wild relatives to improve their use in breeding programs. Crop wild relatives have historically been used in a variety of crops including synthetic wheat, but Australian native wild relatives have been harder to include in the breeding process.

“In the next 10 to 15 years it would be surprising if there is not something coming out that hasn’t got a component of Australian native wild relative in it,” Norton said who is currently involved in the collection of Australian crop wild relatives.

Collection of crop wild relatives is time sensitive

There is an urgency to collect crop wild relatives. Not only are wild species needed now to support changing environmental conditions affecting crops and farming, urbanization is putting crop wild relatives at risk of disappearing.

“We need to collect these sooner rather than later,” Norton told Devex. “Urbanization has a big impact on any native environment, let alone crop wild relatives. We know what species on our target list are more threatened than others — urbanization, flooding and fire are all risks to their security. We certainly have a priority list of species to collect and we need to make sure we target the ones that are under threat first.”

Once the varieties are conserved, breeders and farmers will need to be convinced to start using crop wild relatives. Many are already on board. “Most breeders understand these wild relatives have great potential,” Haga said.

Still, wild relatives can be difficult to work with and produce a lower yield. Haga expects there to be some reluctance, though limited.

“The understanding of the need is increasing and we feel very confident that this material will be used and some of them may be the game changer we are looking for,” she said.

The plans for crop wild relatives

Haga’s 10-year project on crop wild relatives is halfway complete. They are nearing the end of the collection phase and entering the pre-breeding process, before they are able to breed and deliver new species to farmers.

Australian support for the program includes an agreement for additional amount of $5 million. That comes on top of previous support of $21.2 million to the Crop Diversity Endowment Fund, which supports crop diversity globally and with a focus on the Indo-Pacific. Brazil, Chile, Germany, Japan, New Zealand, Norway, Switzerland and the United States are among other supporters of the endowment fund that hopes to reach $850 million. In Australia, further resources are still required to fund and support better seed collection at home.

Globally, plans for crop wild relatives includes raising greater awareness of their potential and importance.

“We have a big job to do to create awareness of the important of crop diversity generally and crop wild relatives specifically,” Haga said. “We have been speaking for years about biodiversity in birds and fish and a range of other animals, but we have talked very little about conserving the diversity of crops. I will fight for all types of diversity, but especially plants.”


 

This article is reposted from the Devex blog with kind permission from the author, Lisa Cornish.

Flipping the symposium

screen-shot-2016-10-24-at-18-38-05

Answers to the question: “Which crop species are most critical with regard to stress resilience?”

Lisa Martin, GPC Outreach & Communications Manager

GPC Executive Director Ruth Bastow and I recently travelled to Australia to hold the GPC’s annual general meeting – but we didn’t go all that way for a one-day meeting! We also took the opportunity to attend ComBio 2016, a large conference jointly hosted by the Australian Society for Biochemistry and Molecular Biology, the Australia and New Zealand Society for Cell and Developmental Biology, and GPC Member Organization the Australian Society of Plant Scientists.

Sadly, one person was conspicuous by his absence – GPC President Bill Davies, who had been due to give more than one talk at the conference, was unable to fly out to Australia at very short notice. While Ruth and our Chair Professor Barry Pogson could cover his talk during the GPC’s own lunchtime symposium, this left Dr Rainer Hofmann’s ‘Abiotic Stress and Climate Change’ session one speaker short at the last minute!

Answers to the question, "Which challenges do these crops face?"

Answers to the question, “Which challenges do these crops face?”

Fortunately Rainer, who happens to be a representative to the GPC for the New Zealand Society of Plant Biology, found a quick solution to the hole in his program: it was time for a bit of audience participation!

The ‘flipped classroom’ is an approach I’d heard of, but was not overly familiar with – however, according to Rainer it is used quite extensively in New Zealand, where plant biologists can be geographically isolated. Unlike the traditional university lecture, in which the teacher gives a presentation and the students go away to consolidate what they have learned with revision notes or problems to solve, the flipped classroom turns this model on its head. Instead, students are given the subject content to learn in advance, then bring their own questions to the lecture.

Arguably, this approach makes better use of students’ contact time and the lecturer’s expertise, and provides a richer and more independent learning experience. This model also works very well in distance learning: topic notes and presentation slides can be emailed out in advance, then a video-linked webinar can be used to connect students and teachers, and a web-tool like Socrative Student can be used to ask and answer questions online.

Answers to the question, "What are key solutions to address these challenges, in the next 3 years and in the longer term?"

Answers to the question, “What are key solutions to address these challenges, in the next 3 years and in the longer term?”

Rainer used this idea to fill the gap in his symposium – and it was great! He asked three important questions, and members of the audience were invited to provide short answers via the Socrative Student platform using their computers, cell phones or tablets – answers were then displayed on a screen in real time. Thank goodness for WiFi! The questions and answers can be seen in the word clouds we’ve created here – the size of the word provides an indication of the frequency of that particular response, so it’s easy to see which were the most and least popular answers. These responses provided useful, engaging stimuli for audience-led discussion – I’d really like to see this model used at other meetings!

The three questions asked were:

  1. Which crop species are most critical with regard to stress resilience?
  2. Which challenges do these crops face?
  3. What are key solutions to address these challenges, a) in the next three years, and b) in the longer term?

What would your answers have been? Leave us a comment below!

Using plants to convert explosives to fertilizers: an interview with Neil Bruce

Neil Bruce

Professor Neil Bruce

This week we spoke to Professor Neil Bruce, whose research at the University of York (UK) focuses on metabolic pathways. His insights into the detoxification of pollutants by plants and microorganisms has led to promising new solutions to help clean up polluting explosives from military testing.

 

Could you begin by telling us a little about your research interests?

I have very broad research interests that often revolve around finding enzymes for biotechnological applications. A particular focus of my lab is the biochemistry and molecular genetics of plant and microbial metabolism of xenobiotic (foreign) compounds, such as environmental pollutants. Elucidating these metabolic pathways often results in the discovery of new enzymes that catalyze interesting chemistries. Being a biologist at heart, I’m interested in the evolutionary origin of these enzymes, but also by studying their structure and function I’m exploring how these enzymes can be engineered to further improve their properties for a particular application, such as environmental remediation or biocatalysis.

 

 

You spoke at the GARNet 2016 meeting about engineering plants to remediate explosives pollution. Could you explain what this problem is and how it affects both people and the environment?

Explosive compounds used in munitions are highly toxic and the potential for progressive accumulation of such compounds in soil, plants, and groundwater is a significant concern at military sites. It is estimated that in the US alone, 10 million hectares of military land is contaminated with components of munitions. The explosives mainly used in artillery, mortars and bombs are 2,4,6-trinitrotoluene (TNT) and Composition B (containing TNT and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)). The US Department of Defense estimated that the clean-up of unexploded ordnance, discarded military munitions and munition constituents on its active ranges would cost between $16 billion and $165 billion. Explosives pollution is, however, a global problem, with large amounts of land and groundwater contaminated by TNT and RDX, including polluted sites in the UK that date back to the First and Second World Wars. Explosives pollution will continue to be a pressing issue while there is a requirement for military to train and the existence of armed conflict requires munitions to be manufactured. There is an urgent need to develop sustainable in situ technologies to contain and treat these pollutants.

 

TNT toxicity in plants

TNT is toxic to plants because of the actions of an enzyme called monodehydroascorbate reductase, which breaks TNT down into a toxic form. Plants lacking this enzyme, such as the mdhar6 mutant plants on the right, can grow very well on TNT-polluted soil. Credit: Johnston et al. (2015).

 

How did you develop the idea of using plants to remove explosives pollution? What benefits do plants have over the microorganisms from which the enzymes are obtained?

We have worked closely with the UK Ministry of Defence and US Army to understand the fate of explosives in the environment. Knowledge of their effects on biological systems is important, as this information can be used to support the management of contaminated sites. We have, therefore, been uncovering the molecular mechanisms behind these detoxification processes in plants, and have used this knowledge, in combination with studies on the bacterial degradation of pollutants, to successfully engineer transgenic plants able to remediate toxic explosive pollutants in a process called ‘phytoremediation’.

An innovative aspect of our work has been the use of genetic engineering to combine the biodegradative capabilities of explosives-degrading bacteria with the high biomass, stability and detoxification systems inherent in plants. While it is possible to find explosives-degrading bacteria on polluted land, they do not degrade the explosives fast enough to prevent leaching into the groundwater. Our engineered transgenic plant systems, however, can efficiently remove toxic levels of TNT and RDX from contaminated soil and water.

 

You mentioned that you are currently testing transgenic switchgrass to remove RDX and TNT pollution in the US. Why did you choose this species and have you considered developing other species suited to different environments?

Plants appropriate for the phytoremediation of explosives need to be adaptable to conditions on military ranges, for example, they need good fire tolerance, and to be able to grow over a wide geographical range. Switchgrass meets these criteria, and is also deep-rooting, can be grown on marginal lands, and researchers can benefit from established methods for genetically engineering switchgrass. We have also been engineering other grass species and have considered fast-growing deep-rooting trees such as poplar.

 

Turning explosives into fertilizers

In a poetic twist, rather than turning fertilizers into explosives, Professor Bruce’s phytoremediating plants convert explosives into fertilizer. Credit: Neil Bruce.

 

How quickly can engineered plants remove this pollution?

In the lab these plants can remove levels of explosives pollution found in the environment within a matter of days. We are currently carrying out field trials with our transgenic plants on a military site in the US, to observe their phytoremediation effectiveness in the real world. If these trials are successful, a number of demonstration studies on contaminated sites will be required to convince end users of the benefits of phytoremediation for remediating and maintaining military land. These demonstration studies will also allow us to evaluate any risks, which will be important to obtain further approval from the US Department of Agriculture to be able to use these plants on a larger scale.

 

What other projects are you working on? Could you elaborate on any recent discoveries?

As well as explosives, we are also working on the use of plants to extract platinum group metals (PGMs) from mining waste. PGMs are used in an ever-expanding array of technologies and demand is spiralling upwards; however, these are rare and expensive to mine. It is essential that these metal reserves are utilized and recycled responsibly, not dispersed and lost into the environment. Plants can take up metals from their environment and, in the case of PGMs, can deposit them as nanoparticles within their tissues. Importantly, we have recently shown that plants containing palladium nanoparticles can also be used to make efficient biocatalysts, and we are currently using synthetic biology in plants to improve palladium uptake and nanoparticle formation.

 


More information:

Johnston, E.J., Rylott, E.L., Beynon, E., Lorenz, A, Chechik, V. and Bruce, N.C. (2015) Monodehydroascorbate reductase mediates TNT toxicity in plants. Science. 349: 1072-1075.

Gunning, V., Tzafestas, K., Sparrow, H., et al. (2014) Arabidopsis glutathione transferases U24 and U25 exhibit a range of detoxification activities with the environmental pollutant and explosive, 2,4,6-trinitrotoluenePlant Physiol. 165: 854-865.

Rylott, E.L.. Budarina, M.V., Barker, A., Lorenz, A., Strand, S.E. and Bruce, N.C. (2011) Engineering plants for the phytoremediation of RDX in the presence of the co-contaminating explosive TNT. New Phytologist, 192: 405-413.

Cassava brown streak: lessons from the field

This week’s post was written by Katie Tomlinson, a PhD student at the University of Bristol, UK, who spent three months as an intern at the National Crops Resource Research Institute in Uganda. She fills us in on the important research underway at the Institute, and how they communicate their important results to local farmers and benefit rural communities.  

Over the summer, I had a great time at the National Crops Resources Research Institute (NaCRRI) in Uganda. I’m currently in the second year of my PhD at the University of Bristol, UK, where I’m researching how the cassava brown streak disease (CBSD) viruses are able to cause symptoms, replicate and move inside plants. I was lucky enough to be given a placement at NaCRRI as part of the South West Doctoral Training Partnership Professional Internship for PhD Students (PIPS) scheme, to experience the problem for myself, see the disease in the field, meet the farmers affected and investigate the possible solutions.

 

Cassava brown streak disease

Cassava brown streak disease symptoms on tubers. Image credit: Katie Tomlinson.

 

Cassava is a staple food crop for approximately 300 million people in Africa. It is resilient to seasonal drought, can be grown on poor soils and harvested when needed. However, cassava production is seriously threatened by CBSD, which causes yellow patches (chlorosis) to form on leaves and areas of tubers to die (necrosis), rot and become inedible.

Despite being identified in coastal Tanzania 80 years ago, CBSD has only been a serious problem for Uganda in the last 10 years, where it was the most important crop disease in 2014–2015. The disease has since spread across East Africa and threatens the food security of millions of people.

NaCRRI is a government institute, which carries out research to protect and improve the production of key crops, including cassava. The focus is on involving farmers in this process so that the best possible crop varieties and practices are available to them. Communication between researchers and farmers is therefore vital, and it was this that I wanted to assist with.

 

Scoring cassava brown streak disease

Scoring cassava plants for Cassava brown streak symptoms. Image credit: Katie Tomlinson.

 

When I arrived I was welcomed warmly into the root crop team by the team leader Dr Titus Alicai, who came up with a whole series of activities to give me a real insight into CBSD. I was invited to field sites across Uganda, where I got to see CBSD symptoms in the flesh! I helped to collect data for the 5CP project, which is screening different cassava varieties from five East and Southern African countries for CBSD and cassava mosaic disease (CMD) resistance. I helped to score plants for symptoms and was fascinated by the variability of disease severity in different varieties. The main insight I gained is that the situation is both complex and dynamic, with some plants appearing to be disease-free while others were heavily infected. There are also different viral strains found across different areas, and viral populations are also continually adapting. The symptoms also depend on environmental conditions, which are unpredictable.

I also got to see super-abundant whiteflies, which transmit viruses, and understand how their populations are affected by environmental conditions. These vectors are also complex; they are expanding into new areas and responding to changing environmental conditions.

It has been fascinating to learn how NaCRRI is tackling the CBSD problem through screening different varieties in the 5CP project, breeding new varieties in the NEXTGEN cassava project, providing clean planting material and developing GM cassava.

 

Tagging cassava plants

Tagging cassava plants free from Cassava brown streak disease for breeding. Image credit: Katie Tomlinson.

 

And there’s the human element…

In each of these projects, communication with local farmers is crucial. I’ve had the opportunity to meet farmers directly affected, some of whom have all but given up on growing cassava.

 

Challenging communications

Communicating has not been easy, as there are over 40 local languages. I had to adapt and learn from those around me. For example, in the UK we have a habit of emailing everything, whereas in Uganda I had to talk to people to hear about what was going on. This is all part of the experience and something I’ll definitely be brining back to the UK! I’ve had some funny moments too… during harvesting the Ugandans couldn’t believe how weak I was; I couldn’t even cut one cassava open!

 

Real world reflections

I’m going to treasure my experiences at NaCRRI. The insights into CBSD are already helping me to plan experiments, with more real-world applications. I can now see how all the different elements (plant–virus–vector–environment–human) interact, which is something you can’t learn from reading papers alone!

Working with the NaCRRI team has given me the desire and confidence to collaborate with an international team. I’ve formed some very strong connections and hope to have discussions about CBSD with them throughout my PhD and beyond. It’s really helped to strengthen collaborations between our lab work in Bristol and researchers working in the field on the disease frontline. This will help our research to be relevant to the current situation and what is happening in the field.

 

Some of the NaCRRI team

Saying goodbye to new friends: Dr. Titus Alicai (NaCRRI root crops team leader), Phillip Abidrabo (CBSD MSc student) and Dr. Esuma Williams (cassava breeder). Image credit: Katie Tomlinson.

 

Interview with Dr. Winfried Peters: Bringing forgotten ideas on plant biomechanics into the 21st century

This week we spoke to Dr. Winfried S. Peters from Indiana University/Purdue University Fort Wayne (IPFW). His research mainly focuses on the biomechanics of plant cells, which led him to take a second look at some of the ideas of botanists in the 19th and early 20th century and use modern techniques to make exciting new discoveries.

Winfried Peters

Dr Winfried S. Peters, Indiana University/Purdue University Fort Wayne (IPFW), next to several tons of land-plant sieve elements!

 

Could you begin by describing your research interests?
I am interested in the biophysical aspects of the physiology of plants and animals. In plants, my research focuses on the mechanics of growth and morphogenesis, and on the cell biology of long-distance transport in the phloem. For both topics, a solid background in the history of the field can be quite helpful – I love studying the old literature to reconstruct the ideas botanists had a century or two ago regarding the functioning of plants.

At the recent New Phytologist Symposium, entitled “Colonization of the terrestrial environment 2016”, you presented fascinating work on the sieve tubes of kelp, which resemble the phloem tubes of vascular plants. What is the purpose of these tubes?
In large photosynthetic organisms, not all parts of the body are truly autototrophic. Some tissues produce more material by photosynthesis than they need, while others produce less than they require or none at all– think of green leaves and growing root tips. Over-producing tissues can act as sources and export photoassimilates to needy sink tissues. Sieve tubes are arrays of tubular cells that mediate this exchange, enabling the rapid movement of photosynthate-rich cytoplasm between sources and sinks.

What techniques did you utilize to investigate the function of these tubes, and what did this reveal?
During my recent sabbatical, I became involved in this project in the lab of my friend and long-term collaborator, Professor Michael Knoblauch. Michael heads the Franceschi Microscopy and Imaging Center at Washington State University, where we studied sieve tubes of the Bull Kelp (Nereocystis luetkeana) using a variety of state-of-the-art microscopy techniques. Most importantly, we employed fluorescent dyes to visualize transport in sieve tube networks. To do this, one needs to work with intact kelp, which is demanding given a thallus size of 12 meters and more. So we moved to Bamfield Marine Sciences Centre on Vancouver Island, where Bull Kelp is a ‘common weed’.

A particularly important result was the pressure-induced reversal of the flow direction in sieve tubes and across sieve plates. This was in line with Ernst Münch’s (1876-1946) theory, who suggested that sieve tube transport was driven by osmotically generated pressure gradients.

 

Nereocystis wounding

An intact Nereocystis luetkeana is kept in a tank (right) while sieve tube transport is studied using a fluorescence microscope. Photo credit: Michael Knoblauch.

How do the biomechanics of the kelp sieve tubes differ from the phloem tubes of higher plants?
Regarding cytoplasmic translocation, there doesn’t seem to be a difference – in higher plants as in kelps, the contents of the sieve tubes move in bulk flow – but wounding responses differ drastically. After wounding, we found that kelps have a massive swelling of the walls, which reduced the sieve tube diameter by more than 70%. By injecting silicon oil into severed kelp sieve tubes we demonstrated that wall swelling was fully reversible, and that the swelling state of the walls depended on intracellular pressure.

Wounding response in kelp

Sieve wall tubes swell after wounding due to changes in intracellular pressure. (Images taken from video below).

Have reversible wall-swelling reactions been observed in other species, and what are the implications of this finding?
We have observed the wall-swelling response in all kelp species examined. Ironically, there is no shortage of drawings and photographs of kelp sieve tubes with swollen walls in the literature over the last 130 years; however, the dynamics of cell behavior remained hidden in plain sight because fixed tissue samples rather than fully functional, whole organisms were studied. Consequently, sieve tubes with swollen walls were misinterpreted as senescent cells. There also are publications on turgor-dependent cell wall swelling in red and green algae, but these ceased around 1930.

Afterwards, wall swelling was completely forgotten, judging from the textbooks. This is remarkable, as Wilhelm Hofmeister (1824-1877), often celebrated as a founding father of plant biomechanics, denied a significant role for osmotic processes in the generation of turgor, the hydrostatic pressure within plant cells. Rather, he maintained that living cells were pressurized by the swelling of their walls. The example of the kelp sieve tube shows how easy it is to remain unaware of wall swelling when it happens right before our eyes. Maybe we should take Hofmeister’s idea seriously once again?

What are the evolutionary implications of your work?
Brown algae and vascular (land) plants are only remotely related, and their sieve tube networks certainly evolved independently of each other. It seems surprising that such sophisticated structures, which serve a complex function that integrates the physiology of the entire organism, have evolved at least twice, but think again. Real cells are not embedded in a totally homogeneous environment, and neither is the cytoplasm within the cell a homogeneous solution. Thus every cell experiences gradients of solute concentrations along its inner and/or outer surface. As a consequence, differential water fluxes across the plasma membrane will occur, resulting in movements of the cell contents. In other words, Münch flow, the cytoplasmic bulk flow driven by osmotically generated pressure gradients, is not a peculiar process operating specifically in sieve tubes, but a ubiquitous phenomenon. Sieve tubes consist of cells that simply do the things cells do, just a little more efficiently as usual. In this view, the repeated convergent evolution of sieve tube networks is not really unexpected.

But kelps resemble land plants in other ways too. As in land plants, kelp cell walls are made of cellulose (at least partly), kelp cells are connected through plasmodesmata, and the kelp life-cycle is a sporophyte-dominated alternation of generations. Evidently, none of these features represents a specific adaptation to life on dry land.


Wound responses including wall swelling in a sieve tube of Nereocystis luetkeana. (Watch for the rapid cell wall swelling between 11 and 14 seconds in!) This video was taken by Professor Michael Knoblauch in collaboration with Dr Winfried S. Peters.
 


If you’d like to know more about this fascinating work, it was been published in the following articles:

Knoblauch, J., Peters, W.S. and Knoblauch, M., 2016. The gelatinous extracellular matrix facilitates transport studies in kelp: visualization of pressure-induced flow reversal across sieve platesAnnals of Botany117(4), pp.599-606.

Knoblauch, J., Drobnitch, S.T., Peters, W.S. and Knoblauch, M., 2016. In situ microscopy reveals reversible cell wall swelling in kelp sieve tubes: one mechanism for turgor generation and flow control? Plant, Cell and Environment39(8), pp.1727-1736.

 

Uncovering the secrets of ancient barley

This week we speak to Dr Nils Stein, Group Leader of the Genomics of Genetic Resources group at the Leibniz Institute of Plant Genetics and Crop Plant Research (IPK). We discuss his recent work on the genomes of 6000-year-old cultivated barley grains, published in Nature Genetics, which made the headlines around the world.

Nils Stein

Dr Nils Stein, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK)

Could you describe your work with the Leibniz Institute of Plant Genetics and Crop Plant Research (IPK)?

The major research focuses of my group, the Genomics of Genetic Resources, are to continue sequencing the genomes of barley and wheat, perform comparative genomics on the Triticeae tribe, isolate genes of agronomic interest, and investigate the genomics of wild barley relatives.

We are currently leading the work to generate the barley reference genome, and we are also partners in several wheat genome sequencing projects. We are genotyping-by-sequencing (GBS) all 20 000 barley accessions in the IPK Genebank, as well as 10 000 pepper accessions as part of a Horizon 2020 project (G2P-SOL) investigating the Solanaceae crop species.
Your recent collaborative paper on the genomic analysis of 6,000-year-old barley grains made headlines around the world. What did this study involve?

This was an interdisciplinary study to sequence the DNA of 6000-year-old barley grains. The grains were excavated by a team of Israeli archaeologists and archaeobotanists led by Prof. Ehud Weiss, Bar-Ilan University, the DNA was extracted and sequenced by ancient DNA specialists Prof. Johannes Krause and Dr. Verena Schünemann in Germany, and the data were analyzed by Dr. Martin Mascher in the context of our comprehensive barley genome diversity information. This allowed the resulting sequence information to be put into a population genetic and ecogeographic context.

Ancient barley

Preserved remains of rope, seeds, reeds and pellets (left), and a desiccated barley grain (right) found at Yoram Cave in the Judean Desert. Credit: Uri Davidovich and Ehud Weiss.

What led you to the realization that barley domestication occurred very early in our agricultural history?

The genome of the analyzed ancient samples was highly conserved with extant barley landraces of the Levant region, which look very similar to today’s high-yielding barley varieties. Although suggestive and tendentious, this told us that the barley crop 6000 years ago looked very similar to extant material. The physical appearance and the archaeobotanical characters of the analyzed seeds also very much resembled modern barley.

 

These barley grains contain the oldest plant genomes reconstructed to date. Did you find any differences between the samples that might give us an insight into the traits that were first selected in the early domestication of the crop?

We have only scratched the surface so far. The major domestication genes controlling dehiscence, brittleness or row-type of the main inflorescence had the same alleles in the ancient samples that are found in extant barley, confirming that these traits were selected for early in domestication. Additional analyses on other genes controlling different traits in barley are still ongoing – bear in mind that many of the genes controlling major traits in barley are still unknown, which complicates the selection of targets for analysis.

Modern barley

Modern barley cultivar. Credit: Christian Scheja. Used under license: CC BY 2.0.

 Do these grains have any genetic variation that we lack at key loci in modern barley lines, for example in stress or disease resistance?

This is matter of ongoing analysis. So far it is obvious that the most genetically similar extant landraces from the Levant region have accumulated natural mutations over the last 6000 years, resulting in additional variation that we don’t find in the ancient sample.

 

What can we expect from the barley genome projects in the future?

The International Barley Genome Sequencing Consortium is preparing a manuscript on the reference sequence of barley. This will allow further analysis of the ancient DNA data with a more complete, genome-wide view, including the consideration of a more complete gene set than has been available so far. Our Israeli collaborators (Professor Ehud Weiss and Professor Tzion Fahima) have more ancient samples of similar quality. We hope we will be able to generate a more comprehensive view of the ancient population genomics of barley in the future, to better address the question of novel ancient alleles and lost genetic diversity.

The Barley Pan-Genome analysis will soon give us a better understanding of the structural variation in the barley genome. Putting the ancient DNA information into this more comprehensive genomic context will be very exciting. We also hope to be able to compare a variety of ancient samples of different ages to more precisely date the event of barley domestication.


You can read the paper here: Genomic analysis of 6000-year-old cultivated grain illuminates the domestication history of barley ($).

Choosing your growth media for plant science

Considering its weedy nature, Arabidopsis thaliana is a fussy little plant. This can be a pain – even tiny environmental fluctuations can have significant impacts on the physiology and development that many of us are investigating.

As silly as it sounds, my labmates and I have spent many months debating the best compost media to use when growing Arabidopsis for research. It began when our trusted compost supplier changed the formula of its peat-based compost, which stressed our plants and turned them a lovely shade of purple! The conversation has continued to develop as we learn about the different media used in other laboratories.

A new paper from Drake et al. at my university (University of Bristol, UK) has added a new depth to the debate, so I thought I’d bring it all to your attention and perhaps receive some other suggestions to consider!

 

Peat-based vs non-peat compost

Arabidopsis growth media

Arabidopsis growth on peat-based and peat-free growth media. Drake et al., 2016.

The experiment, led by Dr Antony Dodd, was designed to test whether peat-based composts could be replaced by alternatives in Arabidopsis research, in an attempt to reduce plant science’s use of unsustainable peat extraction. The researchers grew two ecotypes of Arabidopsis (Col-0 and Ler) on both autoclaved and non-autoclaved composts, including peat-based compost and some formed of coir, composted bark, wood-fiber, and a domestic compost.

In terms of reducing peat use, Arabidopsis unfortunately grew best on the peat-based growing media, although some vegetative traits were comparable in some peat-free composts.

 

Autoclaving compost

This study caught my eye for another reason, however. We always sterilize our compost before growing Arabidopsis to reduce its contamination by fungi and insect pests; however, after learning that manganese toxicity can become a problem, we no longer autoclave it. As you can see in Boyd’s 1971 paper, manganese is converted to a more bioavailable form during the autoclave process, which can be toxic to plants.

Interestingly, Drake et al.’s research revealed no differences in Arabidopsis growth on autoclaved vs. non-autoclaved media, but I expect that in other environmental conditions the elevated manganese availability could become a problem. They did find that the autoclaved soil actually had more issues with mildew and algae, possibly because the natural microbiota had been killed and the compost was therefore easier to colonize.

 

Insecticide treatment

One of the biggest issues our lab has with non-autoclaved soil is the presence of small insects, which can predate our precious plants. A potential alternative to autoclaving is to treat the media with insecticide, such as imidacloprid, a neonicotinoid. However, many labs have stopped using these pesticides; in 2010, Ford et al. showed that several neonicotinoids, including imidacloprid, induce salicylate-associated plant defense responses associated with enhanced stress tolerance, while in 2012, Cheng et al. found 225 genes were differentially expressed in rice plants treated with imidacloprid. In experiments designed to measure precise physiological responses, I’m not convinced that it’s a good idea to use these pesticides!

 

Potential alternatives

To avoid using autoclaves and insecticides, you could consider baking compost overnight at 60°C (140°F) to try and kill fungal spores and insects, freezing the media, and/or using biocontrols to tackle insect pests, such as nematodes or mites.

In the peat vs. non-peat debate, it looks as though peat-based media are still the frontrunners in terms of compost, but hydroponic systems are becoming more popular as a way of tightly controlling nutrient regimes and manipulating whole plants more easily. Check out this video from Associate Professor Matthew Gilliham (University of Adelaide, Australia) to learn more about the technique:

If you have any other suggestions, please leave a comment and share your methods and ideas!

Lessons from the oldest and most arid desert on Earth

Atacama Desert

Image credit: Center for Genome Regulation

The Atacama Desert is a strip of land near 1000 km in length located in northern Chile. With an average yearly rainfall of just 15 mm (close to 0 in some locations) and high radiation levels, it is the driest desert in the world. Geological estimates suggest that the Atacama has remained hyperarid for at least eight million years. Standing in its midst, one may easily feel as though visiting a valley on Mars.

Despite these harsh environmental conditions, it is possible to find life in the Atacama. At the increased altitudes along the western slopes of the Andes precipitation is slightly increased, allowing plant life.

Convergent evolution

The driest and oldest desert in the world acts as a natural laboratory where for 150 million years plants adapted to and colonized this environment. These adaptations are likely present in multiple desert plant lineages, thus providing an evolutionary framework where these traits can be associated with a signature of convergent evolution.

Surviving a nitrogen-limited landscape

Plant in the Atacama Desert

Image credit: Center for Genome Regulation

The interplay of environmental conditions in the transect of the Atacama, ranging from 2500 to 4500 meters above sea level, results in three broad microclimates; Pre Puna, Puna, and High Steppe. These microclimates have different humidities, temperatures, levels of organic matter and even different pH levels, but share one common feature: low nitrogen levels.

To engineer crops with higher nitrogen use efficiency, it is very useful to first learn how plants adapt to growth in low nitrogen environments. Here the Atacama Desert enters into the game. Plants growing in the desert can survive 100-fold less nitrogen below optimum concentrations. Using phylogenetics it is possible to uncover novel genes and mechanisms related to adaptation to these extreme conditions, which have not been discovered through traditional genetic approaches.

Currently, nitrogen fertilizers are widely employed to increase crop yield. In 2008 100 million tons of this fertilizer were used and it is projected that for 2018 the demand for nitrogen will rise to 119 million tons. Regretfully, the production and over-usage of this type of fertilizer has an enormous impact in the environment and human health. Around 60% of the nitrogen introduced to the soil for agricultural purposes is leached and lost. Moreover, nitrogen runoffs to the water cause eutrophication in both freshwater and marine ecosystems, leading to algae and phytoplankton blooms, low levels of dissolved oxygen, and finally the migration or death of the present fauna, forming dead zones such as the one in the Gulf of Mexico.
 

Plants in the Atacama Desert

Image credit: Center for Genome Regulation

Nitrogen fertilizers are not the only major concern in modern agricultural procedures. The co-localization of drought and low nitrogen levels is especially detrimental for plant growth and development. We need to support not only the nutritional requirement of an expanding global population but also new energetic strategies based on production of biomass for biofuels on marginal nutrient poor soils. In order to increase crop yields while reducing the environmental impact of nitrogen fertilizers, it is necessary to develop new agricultural strategies and cutting edge technologies.

Learning from the desert

What if we could profit from the extraordinary plants that have had thousands of years to learn how to cope with nitrogen scarcity, drought and extreme radiation? Specifically, can we unravel the genes and mechanisms that allow them to survive in such a barren place?

Atacama Desert

Image credit: Center for Genome Regulation

Over the past three years our group has identified 62 different plant species that inhabit the Atacama Desert, and established a correlation between their habitat attributes and biological characteristics. Using tools such as whole transcriptome shotgun sequencing or RNA-Seq complemented with different bioinformatics approaches, we have identified over 896,000 proteins that are expressed in these conditions.

In this way we aim to learn which processes are highly utilized in these “extreme survivors” compared to similar species that are present in the deserts of California, where the climatic conditions are similar but there is no nitrogen scarcity. That is how we expect to find new mechanisms (or, more precisely, very old mechanisms) that enable plants to survive and grow efficiently in extreme environments.


 
Susana Cabello

Dr Susana Cabello

Written by Dr Susana Cabello, Center for Genome Regulation, Millennium Nucleus for Plant Systems and Synthetic Biology, Chile. Susana would like to acknowledge Maite Salazar & Rodrigo Gutierrez for their suggestions and edits.