Plant Artificial Chromosome Technology

Established GM technologies are far from perfect

The first genetically modified (GM) crops were approved for commercial use in 1994, and GM crops are now grown on over 180 million hectares across 29 countries. The most used forms of genetic modification are systems that result in herbicide resistance or expression of the Bt toxin in maize and cotton to provide protection against pests such as the European corn borer. These systems both require few novel genes to be introduced to the plant, and allow more efficient use of herbicides and pesticides, both of which are harmful to the environment and human health. Current systems of genetic modification usually involve

Agrobacterium tumefaciens is used to genetically engineer plants in the lab. In nature this bacteria uses its ability to alter plant DNA to cause tumours.

Agrobacterium tumefaciens is used to genetically engineer plants in the lab. In nature this bacteria uses its ability to alter plant DNA to cause tumours. Image by Jacinta Lluch Valero used under Creative Commons 2.0.

the use of Agrobacterium vectors, direct transformation by DNA uptake into the plant protoplast, or bombardment with gold particles covered in DNA. However, current systems of transformation are far from perfect. Many beneficial traits such as disease resistance require stacking of multiple genes, something that is difficult with current transformation systems. Furthermore, it is essential that transgenes are positioned correctly within the host genome. Current systems of genetic modification can insert genes into the ‘wrong’ place, disrupting function of endogenous genes or having implications for down or upstream processes. An additional problem is that transfer of transgenes from one line to another requires several generations of backcrossing. However, the past two decades have seen great developments in microbiology. Many new tools and resources are now available that could greatly enhance the biotechnology of the future.

 

New technologies

Many new and emerging technologies are now available that could transform plant genetic engineering. For example, high throughput sequencing and the wide availability of bioinformatics tools now make identifying target genes and traits easier than ever. Technologies such as site-specific recombination (SSR) and genome editing allow specific regions of the genome to be precisely targeted in order to add or remove genes. Artificial chromosome technology is also part of this emerging group that could be of benefit to plant science. Synthetic chromosomes have already been used in yeast, and widely studied in mammalian systems due to their potential use in gene therapy. Although there have so far been no definitive examples in plants, work has been done in maize that shows the potential of the technology for use in GM crops.

 

Building an artificial chromosome

A minichromosomes is a small, synthetic chromosome with no genes of its own. It can be programmed to express any desirable DNA sequence that could encode for one, or a number, of genes. An ideal minichromosome would be small and only contain essential elements such as a centromere, telomeres and origin of replication. Once introduced into the plant the minichromosomes should be designed such that interference with host growth and development is minimal. A key requirement is that the chromosome is stable during both meiosis and mitosis. This would ensure introduced genes do not become disrupted or mutated during cell division and reproduction. Gene expression would therefore remain the same for many generations. Finally, the DNA sequence on the minichromosomes could be designed such that it is amenable to SSR or gene editing systems. This would allow re-design and addition of new traits further down the line.

 

Potential advantages of artificial chromosomes

Plant artificial chromosomes (PACs) have many advantages over traditional transformation systems. For example, to confer complex traits such as disease resistance and tolerance to abiotic stresses such as heat and drought, multiple genes are required. This is not easy with current methods of modification.

PACs could offer a new way to introduce beneficial traits to our crops plants and feed a growing population.

PACs could offer a new way to introduce beneficial traits to our crops plants and feed a growing population.Image by Seattle.Romer. Used under Creative Commons 2.0.

However, PACs allow an almost unlimited number of genes to be integrated into the host system. A further possibility that comes from being able to add multiple genes is the addition of new metabolic pathways into the plant. This could allow us to change the nutrients produced by a plant to benefit our diets. Additionally, in a contained environment, plants could be used as a cheap, sustainable way to produce pharmaceuticals. A second major benefit of PACs is that they avoid linkage drag. This is when a desirable gene is closely linked to a deleterious gene that acts to reduce plant fitness. Where this linkage is very tight even repeated backcrossing cannot separate out the genes. Design of new DNA sequences completely avoids this problem, and could allow us to select out detrimental traits from out crop plants.

 

Regulations for novel biotechnology

Emerging technologies pose new questions to policy makers regarding GM regulation. For example, the use of genome editing, whereby specific sites in the genome are targeted and modified, produces an end product with a phenotype almost identical to one that could be achieved through conventional breeding. This sets genome-edited crops apart from other transgene-containing GM material. For this reason many now argue that genome-edited crops ought not to come under current GM regulations. Much of this argument centres on whether or not to regulate the scientific technique used to produce a crop, or to regulate the end product in the field. For more information on genome editing including current regulations and consensus, see the links at the end of this article.

 

PACs pose a different set of problems entirely. Minichromosomes would be foreign bodies in the plant, and gene stacking within these introduces even more foreign genes than is possible with current technologies. This would require extensive assessment of both environmental and health effects prior to commercialization. Currently regulatory approval costs around $1-15 million per insertion into the genome. These heavy charges may discourage the further development of minichromosomes technology. However, with PACs it is possible that a particular package of genes could be assessed once, and then transferred into numerous cultivars. This would eliminate the requirement to individually engineer and test every cultivar, so perhaps saving time and money in the long term.

 

More information on genome editing:

Sense about science genome editing Q & A

The regulatory status of genome-edited crops

The Guardian article on genome editing regulation

A proposed regulatory network for genome edited crops in Nature

A recent workshop on the CRISPR-CAS system of genome editing was held in September 2015 by GARNet and OpenPlant at the John Innes Centre in Norwich, UK. You can read the full meeting report here.

 

 

 

 

 

 

 

 

 

 

 

Integrated Pest Management Systems

Herbivorous pests can devastate crops, with huge economic and social impacts that threaten global food security. In 2011 scientists warned that biological threats, including pests and pathogens, account for a 40% loss in global production and have the potential for even higher losses in the future.

A farmer sprays pesticides on her crop

A farmer sprays pesticides on her crop. From IFPRI – IMAGES. Used under Creative Commons 2.0.

In the 1950s and 1960s huge amounts of pesticides were being used in agriculture, with negative effects on both humans and ecology. Pests and pathogens were developing resistance to pesticides, and to counteract this chemical companies were developing ever stronger, more expensive chemicals.

Perry Adkisson and Ray Smith, both entomologists, noted the harmful effects on the economy and environment of the overuse of synthetic pesticides. Working together they identified practical approaches to pest control that minimized pesticide use. They developed and popularized integrated pest management (IPM) systems, for which they won the World Food prize in 1997.

 

“Integrated Pest Management (IPM) means the careful consideration of all available pest control techniques and subsequent integration of appropriate measures that discourage the development of pest populations and keep pesticides and other interventions to levels that are economically justified and reduce or minimize risks to human health and the environment. IPM emphasizes the growth of a healthy crop with the least possible disruption to agro-ecosystems and encourages natural pest control mechanisms.” FAO definition

 

What is IPM?

IPM is an approach to crop production that considers the whole ecosystem, integrating a number of management techniques, rather than focusing all resources on a single practice such as pesticide use. Adkisson and Smith identified a number of principals around which successful IPM should be based:

Firstly, crop varieties should be selected that are appropriate to the culture and local environment. This would ensure the crop species is already adapted to local conditions, and may have some defense mechanisms to protect itself from biotic and abiotic stresses.

Secondly, IPM is based around pest control rather than complete eradication. Therefore, maximum tolerable levels of the pest that still enable good crop yields should be identified and the pests should be allowed to survive at this threshold level, although allowing a number of pests to exist within the crop requires continual monitoring. Good knowledge of pest behavior and lifecycle enables the prediction of where more or less controls are required.

Finally, when choosing a method of control, both mechanical methods, such as traps or barriers, or appropriate biological control are preferential. However, pesticides can be integrated into the plan if necessary, providing use is responsible and not in excess of requirements. Some really cool practices are now emerging that can be used as part of an IPM system around the world.

 

Enhancing biological control

Simply reducing pesticide use can actually lead to increased yields, as farmers in Vietnam discovered when scientists convinced them to try it for themselves. Their nemesis, the brown planthopper (Nilaparvata lugens), is increasingly resistant to insecticides, with devastating outbreaks becoming more common. Rice farmers found that by stopping their typical regular insecticide sprays, the planthopper’s natural predators such as frogs, spiders, wasps and dragonflies were able to survive and remove the pests, giving farmers a 10% increase in harvest income. This improved biological control is a key component of IPM.

Brown Planthopper

The Brown Planthopper (Nilaparvata lumens) on a rice stem. From IRRI photos. Used under Creative Commons 2.0.

 

Push-pull technology

Push-pull agriculture has been very successful in Kenya, where stemborer moths can cause vast yield losses in maize with estimated economic impacts of up to US$ 40.8 million per year. Push-pull technology uses selected species as intercrops between the main crops of interest. Intercrops work in two ways, by pushing pests away from the economically valuable crop, and pulling them towards a less valuable intercrop. The stemborer moth push-pull system uses Desmodium (Desmodium uncinatum) to repel stemborer moths. Desmodium species are small flowering plants that produce secondary metabolites that repel insects. Moths are then attracted to the surrounding napier grass instead.

Aside from controlling the stemborer moth, this system has a number of additional benefits. Desmodium suppresses the growth of Striga grass (a devastating weed that you can read about here) via a number of mechanisms, primarily through interfering with root growth. Additionally, the intercrop species can be used for animal fodder and improve soil fertility. The multiple benefits and success of this system has meant push pull has now been adopted by over 80,000 small-holdings in Kenya and is being rolled out to Uganda, Tanzania and Ethiopia.

 

Stem borer larva feeding on a maize stem.

Stem borer larva feeding on a maize stem. From International Institute of Tropical Agriculture. Used under Creative Commons 2.0.

Abrasive weeding

Abrasive weeding is a relatively new technique that involves firing air-propelled grit at a crop to physically kill any weeds growing between crop rows. One issue with this method is that it indiscriminately damages the stem and leaf tissue of both crops and weeds, but grit applicator nozzles are available to more directly target the base of the stem to minimize collateral damage. A recent study found abrasive weed control reduced weed density by up to 80% in tomato and pepper fields, with 33-44% increases in yield.

Maize cob or walnut shells are currently the most frequently used grits, but the technique offers the exciting possibility of combining fertilization and weed control in one step, which could reduce time and cost to the farmer. For example, soybean meal is able to destroy plant tissues when fired from the gun, and has high nitrogen content that is released slowly into the soil over a period of at least three months, making it an ideal source of fertilizer.

 

Flowers of the Global Plant Council

A while ago we published a blog post about the sequencing of the Bauhinia genome. Bauhinia x blakeana is the national flower of Hong Kong, so naturally this sparked our interest in the global importance of flowers as national symbols, such as the English rose. Here we list just a few of the more interesting and unusual plants that are the national symbols of countries hosting GPC member organizations.

India       Indian Society for Plant Physiology

Nelumbo nucifera

The Lotus Plant

The Lotus Plant (Nelumbo nucifera) is an aquatic plant in the Nelumbonaceae family, and is the national flower of India and Vietnam. Image by alterna used under Creative Commons 2.0.

The lotus plant (Nelumbo nucifera) is considered sacred in the Buddhist and Hindu religions, and been used for over 7000 years in Asia as a source of food, herbal remedy and fibers for clothing. In 2013 its genome was sequenced, allowing its phylogenetic history and adaptations for the aquatic environment to be more fully understood.  For example, the plant has a number of genes enabling its adaptation to the nutrient poor soils in waterways, altering its novel root growth, iron regulation and phosphate starvation.

Researchers at the University of Adelaide, Australia, showed that the lotus actually has the ability to regulate the temperature of its flowers, maintaining them between 30 and 36 °C even when air temperature dropped below this. Quite how or why it does this is still unknown, but warmer flowers could play a role in attracting cold-blooded insects and increasing their activity once on the flowers to enhance pollination. An alternative explanation could be that warmer temperatures are required for pollen production.

Another fantastic fact about the lotus is seed viability. A 1300 year old lotus fruit found in a dry lakebed in China was successfully germinated, providing an insight into the aging process of fruits and other organisms

Australia      Australian Society of Plant Scientists

Acacia pycnantha

Acacia

The golden wattle (Acacia pycnantha) is a member of the Fabaceae family. The plant is a small tree that can grow up to 12 meters high! In Australia the 1st September is National Wattle Day. Image by Sydney Oats used under Creative Commons 2.0.

The Australian national flower is the Acacia pycnantha, or wattle, first described in 1942. Its name comes from the Greek pyknos (dense) and anthos (flowers) describing the dense groups of flowers that form on the tree. The wattle is an important source of tannins, and as such has been introduced to parts of southern Europe such as Italy and Portugal in addition to India and New Zealand. The wattle is also found in South Africa where it has now become an invasive pest, and various methods of biological control such as gall forming wasps (Trichilogaster signiventris) are being used to control populations.

Galls on Acacia

Galls on a wattle tree from T. signiventris. Eggs are laid by the wasp in the buds of flower heads and the hatched larvae induce gall formation which prevents flower development. This in turn prevents pollination and continued propagation of the Wattle population. Image by Sydney Oats used under Creative Commons 2.0.

Japan      The Japanese Society of Plant Physiologists

Yellow Chrysanthemum

Yellow Chrysanthemum

The yellow Chrysanthemum is a member of the Asteraceae family. Species of the Chrysanthemum enus are popular ornamental plants, and as such many hybrids and thousands of cultivars in a variety of colors and shapes can be found. Image by Joe deSousa used under Creative Commons 1.0.

Although cherry blossom is often the flower most associated with Japan, yellow Chrysanthemum flowers are equally as important. The flower is used as the Imperial Seal of Japan and on the cover of Japanese passports. Species of the genus Chrysanthemum are members of the Asteraceae (daisy) family.

Two species of the Chrysanthemum genus, C. cinerariifolium and C. coccineum, synthesize pyrethrum compounds, which attack insect nervous systems. As such these species make good companion plants in the field, repelling insects from economically valuable neighboring plants that do not have their own defense mechanisms. The naturally produced toxins are widely used in organic farming, and many synthetic versions are also available commercially.

South Africa      African Crop Science Society

Protea cynaroides

King Protea

The king protea (Protea cynaroides)  is a member of the Proteaceae family and the national flower of South Africa. The South African cricket team has the nickname the Proteas, after the flower. Image by Virginia Manso, used under Creative Commonds 2.0.

The king protea (Protea cynaroides) can grow up to 2 meters in height and comes in several colors and varieties. The plant grows in harsh, dry regions prone to wildfire, and as such has a number of adaptations for the environment. For example, a long tap-root is used for accessing deep water, and tough leathery leaves are resilient to both biotic and abiotic stress. The protea has a thick underground stem with many dormant buds. After a wildfire these dormant buds can become active, forming new stems allowing the plant to survive!

The king protea is only one species within the large Proteaceae family, 120 species of which are now endangered listed on the IUCN Red List of threatened species. The Protea Atlas Project aims to map the geographical location of proteas through Southern Africa in order to help preserve the family. In addition to protea, Southern Africa is home to around 24 000 plant taxa, 80% of which occur no where else in the world. A wider objective of the Protea Atlas Project is to map species-richness patterns in Southern Africa. The distribution of Protea plants within the region largely seems to match the species-richness patterns of other plant species, and therefore proteas are being used as surrogates for plant diversity. Find out more about the project and get involved here.

Germany and Estonia      EUCARPIA, EPSO, FESPB, SPPS

Centaurea cyanus

Cornflower

The cornflower (Centaurea cyanus) is a member of the Asteraceae family, like the Chrysanthemum. Image by Anita used under Creative Commons 2.0.

We have a large number of European and Scandinavian member groups, and choosing one flower to represent all of those was a challenge. However, the humble Cornflower seemed an appropriate choice to represent our European societies. This member of the daisy family is not only the national flower of Germany and Estonia, but has a place in many Scandinavian cultures being the symbol for a number of political parties in Finland and Sweden.

In the past this beautiful flower was regarded as a weed, but now due to intensive agricultural practices has become endangered. Cornflowers have many uses in addition to being an ornamental plant. The plant is used in many blends of herbal tea, flowers are edible in salads, and the blue coloring can be used as a clothes dye.

Canada           Canadian Society of Plant Biologists

Acer 

Although not technically a flower, the leaf of the maple tree  is such an iconic symbol on the Canadian flag we just had to include it (we are the Global Plant Council after all). There are many species of maple tree in the genus Acer, which can be distinguished from other genus of trees by their distinctive leaf shape. The most important species of maple in Canada is probably Acer saccharum, the sugar maple. The sap of this species is the major source of maple syrup, and its hard wood is popular for use in flooring and furniture.

Maple

Acer saccharum, the sugar maple, in Autumn. Image by Mark K. used under Creative Commons 2.0.

The sugar maple grows throughout the USA and Canada, favoring cooler climates and is a very shade tolerant species.  Despite this, the sugar maple is now in decline in many regions. It is highly susceptible to increased levels of air pollution and changes to salt levels. As such the species is now being replaced in many regions by the hardier Norway Maple.

Argentina                  Argentinian Society of Plant Physiology

Erythrina crista-galli 

E. crista-galli, the cockspur coral tree, is the national tree in Argentina. Also known in Argentina as the ceibo, the bright red flower of this tree is also the national flower of Argentina and Uruguay.

Cockspur

The bright red flowers of E.crista-galli are the national flowers of Argentina and Uruguay. Image by Gabriella F.Ruellan used under Creative Commons 2.0.

The small tree is a legume from the family Fabaceae. Characteristically of species from this family, the fruit of the cockspur coral tree are dry pods, and the roots have nodules containing nitrogen fixing bacteria making them important for increasing the available nitrogen in the soil. Although native to South America, the tree is also naturalized in Australia, where it is becoming an emerging environmental weed. The tree is invading waterways and wetlands displacing native species, and its spread is now being controlled in New South Wales.

If your country has a particularly interesting national flower that we have missed let us know! Perhaps we can include it in a future blog post.