Only three plant species -- rice, wheat, and maize -- account for most of the plant matter that humans consume, partly because of the mutations that made these crops the easiest to harvest. But with CRISPR technology, we don't have to wait for nature to help us domesticate plants, argue researchers.
Led by the University of Adelaide in Australia and the Leibniz-Institute of Plant Genetics and Crop Plant Research (IPK) in Germany, the research will give plant-breeders new targets for developing lines of barley with resistance to powdery mildew.
The two genes, HvGsl6 and HvCslD2, were shown to be associated with accumulation of callose and cellulose respectively. These two polysaccharides play an important role in blocking the penetration of the plant cell wall by the powdery mildew fungus.
Published in two separate papers in the journal New Phytologist, the researchers showed that by "silencing" these genes, there was lower accumulation of callose and cellulose in the plant cell walls, and higher susceptibility of barley plants to the fungus. Conversely, over-expressing HvCslD2 enhanced the resistance in barley.
"Powdery mildew is a significant disease of barley wherever it is grown around the world, and resistance to the fungicide most commonly used to control it has been recently observed," said Alan Little, a senior research scientist at the University of Adelaide, with the ARC Centre of Excellence in Plant Cell Walls in the School of Agriculture, Food and Wine, in a press release.
"If we can develop barley with improved resistance to powdery mildew, it will help barley producers increase yields and maintain high quality."
In the plant and pathogen co-evolutionary battleground, host plants have evolved a wide range of defence strategies against attacking pathogens.
One of the earliest observed defence responses is the formation of cell-wall thickenings called papillae at the site of fungal infection. They physically block the fungus from penetrating the plant cells.
In barley, the papillae contain callose and cellulose as well as other polysaccharides, but the genes involved in accumulation of these carbohydrates in the cell wall have not been identified.
"Our results show that these novel genes are interesting targets for improving cell-wall penetration resistance in barley and maybe other cereals against fungal intruders," said Patrick Schweizer, head of the Pathogen-Stress Genomics Laboratory at IPK.
"Now we can use these genes to identify molecular markers for breeding enhanced resistance into modern barley."
The two papers can be read online here and here.
May 31, 2016 - A new generation of plants better adapted to mitigate the effects of environmental change could be created following a fundamental step towards understanding how plants are able to retain a memory of stress exposure.
The research, led by the University of Warwick and published in the journal eLife, provides the first compelling evidence that plants have evolved ways to remember previous exposures to stress, in this case high salinity conditions, which can help subsequent progenies withstand the same stress in future.
The international study, led by Dr Jose Gutierrez-Marcos from Warwick's School of Life Sciences, has revealed that this "stress memory" is programmed epigenetically by chemical modifications in the form of cytosine methylation to the DNA at specific locations of the plant genome.
"With the rising threat of climate change, there is a need to create future plant varieties that provide stronger yields and are able to grow in a wide range of challenging climates. By uncovering the mechanisms by which plants are able to remember previous exposures to stress and develop adaptive responses, we have opened up the possibility of breeding a new generation of plants to address these requirements."
The new research has found that in the absence of stress this memory is gradually reset especially when transmitted through the male lineage. In addition, the researchers found that stress memory can be fixed by mutations in genes responsible for resetting DNA methylation.
"Before our discovery, the extent of a stress memory in plants was unrecognized but we now have evidence for some of the molecular mechanisms implicated in this process. The next step is to manipulate plant memory and translate this knowledge to produce crops that are better adapted to environmental change"
Apr. 22, 2016 - Faced with a pathogen, important signaling chemicals within plant cells travel different routes to inform the plant to turn on its defense mechanisms, according to a recent University of Kentucky (UK) study.
Plant pathologists Aardra and Pradeep Kachroo study how plants fend off secondary infections, a defense mechanism known as systemic acquired resistance. In previous studies, the UK College of Agriculture, Food and Environment scientists identified several chemicals within plant cells that help trigger this resistance. Their most recent study, published in Cell Host and Microbe, looked at the paths three of those chemicals travel. Understanding these pathways and chemicals may shed light on new ways scientists can help plants fend off a wide range of pathogens.
"Animals have a circulatory system that makes it very easy for one part of the body to communicate with another," Aardra Kachroo said. "This is not the case for plants, which makes communication more difficult between various parts. That's why it's important for scientists to understand how that happens."
Their research found that two of the chemicals travel through the same opening between cells, called the plasmodesmata. They are helped through this "doorway" by proteins that also control the opening and closing of the "door."
The third signaling chemical, salicylic acid, the active ingredient in aspirin, travels a different route, going out of one cell into the plasma membrane and then into another cell.
"This is a similar route via which aspirin in taken up in the human body," Pradeep Kachroo said.
In plants, after moving to the neighboring cell, salicylic acid can also shut the door in between the cells that the other two chemicals traveled through.
"This knowledge is very relevant to how we use chemicals for protecting our crops in the field," Pradeep Kachroo said.
The Kachroos' results suggest that although current strategies of using chemicals that activate the salicylic acid pathway maybe an effective short-term strategy to manage specific diseases, it could potentially have long-term negative repercussions on the plant's inherent ability to induce broad-spectrum systemic immunity.
What if corn breeders had access to molecular markers for qualities like Gibberella ear rot resistance and kernel dry down rate? Researchers at Agriculture and Agri-Food Canada’s Ottawa Research and Development Centre (ORDC) have begun to understand the molecular mechanisms influencing these traits, which means corn breeding is about to get smarter – and faster.
“We’re always trying to develop new inbreds of corn with resistance to Gibberella ear rot, so we have several lines developing in our pipeline over the next few years,” says Lana Reid, a research scientist with expertise in corn breeding and genetics.
“We’re the only public breeding program in Canada that releases public inbreds, and the demand has been increasing.”
ORDC’s previous releases include CO441 and CO449, which have the highest Gibberella resistance of any publically released maize lines in the world. This year, the centre is releasing the first lines they’ve ever developed with common rust resistance. Within the next several years, Reid says the ORDC will release between 10 and 20 lines with resistance to common maize diseases.
Reid has collaborated with French, Spanish and Chinese researchers in analyzing the biochemical mechanisms for resistance. “Why is something resistant? Why is it so resistant? These are people coming forward saying this is why,” Reid says.
But important discoveries are being made right at ORDC. Linda Harris, a research scientist in cereal/fungal genomics, is working with Reid on an industry-driven improved corn genetics project. Harris uses next-generation sequencing technology to map Gibberella ear rot resistance in maize.
“A number of different sources of resistance have been identified in cereals, maize and wheat, but we don’t know the exact mechanism of resistance at the molecular level,” she says.
A few years ago, Harris crossed CO441, which has good silk and kernel resistance to ear rot, with B73, the susceptible United States inbred that is the source of the public maize genome sequence. Using a large hybrid ear resulting from that cross, Harris developed 410 separate lines from the seeds of the ear, where each line was descended from a single seed and has a different homozygous mosaic background – or a different mix of the parents’ genetics.
“We screened those 410 lines for silk and kernel resistance over several seasons, used the low-cost genotyping by sequencing method to obtain over 1000 molecular markers across the genomes, and then we looked to see which regions of the genome were responsible for resistance,” Harris says.
The project, which is funded by Growing Forward 2 and the Canadian Field Crop Research Alliance, which includes the Manitoba Corn Growers Association, began in April 2013 and will continue to March 2018.
So far, their findings have been promising.
Aida Kebede, a post-doctoral fellow at ORDC, is looking for regions of the genome responsible for resistance. She identified 10 genomic locations providing Gibberella resistance, of which four were common between silk and kernel modes of entry. And she also found some genotypic correlations between disease severity and agronomic traits – meaning that agronomic traits have a role to play in disease resistance.
In other words, Gibberella ear rot resistance and agronomic traits like kernel dry down are interlinked.
To analyze the expression of these traits in maize, Kebede conducted a field experiment for two years before extracting RNA samples. Now, Kebede is using RNA sequencing to try to get to the heart of the relationship between disease resistance and agronomic traits.
“At the moment I’m working on gene expression data analysis for identifying candidate genes for Gibberella resistance using RNA sequencing,” says Kebede.
“Because we have already seen there is a relationship between Gibberella resistance and kernel dry down rate, we want to use one trait as an indirect selection criteria for the other trait,” she says. “Kernel dry down rate is much easier to measure, so we try to indirectly select for Gibberella resistance by selecting for maize lines with fast kernel drydown rate.”
Kebede says breeding for Gibberella ear rot resistance is intense, requiring a great deal of resources and human labour. If kernel dry down rate can be used as an indirect selection for Gibberella resistance, the breeding process will be streamlined by reducing the cost for independent disease screening experiments.
Harris says the project is still at the validation stage, but the team hopes their work will soon result in molecular markers that Reid can incorporate into her breeding program. “It’s very labour intensive to screen for resistance. If we can pre-screen for certain markers that would be much easier,” Harris says.
Kebede is hopeful that the program will result in a more efficient breeding process. “Finding the chromosomal regions and the candidate genes will speed up the breeding process, so that transferring resistance genes to hybrid corn will be much easier. That is the achievement. And farmers will get resistant hybrids much faster than before,” she says.
Jan. 11, 2016, Saskatoon, SK - Winter wheat in Western Canada is receiving a huge boost as a crop with the recent addition of partner, The Mosaic Company Foundation, the newest member of the Western Winter Wheat Initiative (WWWI). The Mosaic Company Foundation is now helping to fund the WWWI with an investment of $1 million over the next three years.
"We are fortunate to have such great industry support for winter wheat as a crop here on the Prairies," says Paul Thoroughgood, with the WWWI. "Now that The Mosaic Company Foundation is on board, we are able to continue supporting the growth of winter wheat across Manitoba, Saskatchewan and Alberta, and have professional agronomists available to help farmers improve their bottom lines."
An excellent fit in crop rotations, winter wheat complements all the WWWI partners' visions for a sustainable agricultural landscape. Not only is winter wheat one of, if not the most, high-yielding and profitable crops grown on the Prairies, it also has a more efficient use of crop inputs, uses reduced tillage, and provides wildlife habitat, making it one of the most environmentally and conservation-friendly crops around.
"As global demand for food increases, farmers are working to sustainably intensify the amount of food they grow while enhancing environmental protection. Winter wheat is a great example of this in action," says Mark Kaplan, Board President of The Mosaic Company Foundation and Senior Vice President of Public Affairs at The Mosaic Company. "We are pleased to support the Western Winter Wheat Initiative as it helps farmers optimize yields and improves nutrient stewardship and water quality outcomes."
The WWWI is a strong advocate for responsible farm management practices and the 4R's for Nutrient Stewardship and recognizes The Mosaic Company Foundation as the perfect addition to its efforts.
Promoting winter wheat as a great sustainable crop option for farmers in Prairie Canada, the WWWI offers expert agronomic support and funds breeding and agronomy research programs thanks to like-minded industry partners Bayer CropScience, Ducks Unlimited Canada, Richardson International Limited, and now, The Mosaic Company Foundation.
Dec. 9, 2015 - Plants are regularly challenged by a variety of environmental stresses such as drought, flooding, salt, and low-nutrient levels. These stresses negatively affect plant growth and reduce the productivity of crops. Many wild plants have evolved mechanisms to meet these challenges while domesticated crops are less resilient. Understanding the mechanisms that wild plants use will enable the development of improved crop varieties than can be grown on lands that are currently unsuitable for crops and, in the face of changing climatic conditions, help to feed a rapidly growing global population.
"This project has broad implications for British Columbians, Canadians and people around the world because stress-resistant crops will improve food security," says Dr. Alan Winter, president and CEO of Genome BC. "The ability to understand the mechanisms allowing plants to mitigate these stressors will enable the development of crops capable of growing in previously unsuitable habitats and bring previously marginal farmlands into production."
Sunflowers are an ideal model system for better understanding mechanisms that plants use to combat environmental stresses because their wild counterparts have adapted to a variety of extreme habitats. A $7.9 million project funded by Genome British Columbia, Genome Canada and other partners is investigating how wild sunflower plants have become more resistant to environmental stressors. The international team, led by the University of British Columbia (UBC)'s Dr. Loren Rieseberg and the University of Georgia's John Burke, is focusing on the genetic basis of stress resistance. Worldwide sunflower production generates approximately $20 billion in revenue and is the only oilseed in the Global Crop Diversity Trust's list of 25 priority food security crops. Because it is grown widely in developing countries for food, the project is partnering with leading public and private sector sunflower breeding programs around the world, including in Sub-Saharan Africa.
"Stress-resistant cultivars will stabilize production in the face of environmental stressors in Sub-Saharan Africa, thereby reducing the potential for malnutrition and its social and economic costs," says Dr. Rieseberg, Professor and Canada Research Chair, Department of Botany, UBC. "Such cultivars will also be better adapted to new climates that are predicted for Canada and developing countries."
The project, Genomics of abiotic stress resistance in wild and cultivated sunflowers, will identify and fully characterize the genetic basis of stress resistance in sunflowers and create resources that will enable partners from the public and private sectors to efficiently breed stress-resistant, high-yield cultivars. The team will also develop models to predict likely yields of the new cultivars in different soil and climate conditions across Canada. In addition, the team will address the role of international treaties in sharing plant genetic resources developed from this project for growers in Canada and around the world.
The expanded sunflower production made possible in Canada by the new cultivars is expected to yield up to $230 million USD annually after ten years. Worldwide, the impact will be substantial, as no other oilseed can maintain the stable yields across as wide a range of environmental conditions as that predicted for the new sunflower cultivars.
The project was funded through Genome Canada's 2014 Large-Scale Applied Research Project Competition: Genomics and Feeding the Future. In addition to Genome BC and Genome Canada, other funding partners the include the U.S. National Science Foundation (NSF), University of Georgia, Global Crop Diversity Trust, Institut national de la recherche agronomique (INRA) Toulouse, KWS Seeds, Advanta Semillas SAIC, Biogemma, Nuseed Americas and SAP AG.
A quiet revolution in pest control is underway in labs in Canada and around the world. RNA interference (RNAi) is a natural, biological process by which RNA molecules suppress or “silence” genes targeted as threats. Discovered in the 1990s, RNAi technology has since become a research and development priority across the life sciences, with promising applications in antiviral therapy, cancer treatments and biotechnology.
The range of potential applications of RNAi in agriculture is extraordinary – the technology can be used to increase yields and improve agronomic performance; metabolic changes have been achieved in crops ranging from coffee to peanut to petunia. And RNAi shows great promise for pest and pathogen control. Using RNAi, researchers have achieved increased resistance to virus diseases, nematodes, bollworm, powdery mildew and leaf rusts in a range of crops.
“RNAi is going to be an unprecedented game changer,” says Curtis Rempel, vice-president of crop production with the Canola Council of Canada (CCC). “From the canola industry’s perspective, it’s a big priority, for a whole host of reasons. We’re keen to find out what can be done to control different insect pest species.”
The CCC is currently in talks with the entire canola value chain – life science companies, producers, handlers and crushers – to create public/private partnerships to develop RNAi for the canola industry.
“We think there needs to be a consortium around this,” Rempel says. “How will farmers benefit from the technology? How can we implement RNAi so it doesn’t stay as a journal article?”
Thus far, RNAi for pest control in Canada has mainly focused on crops such as corn and soy, but Rempel believes it has enormous potential for the canola industry as well.
In Canada, public research agendas are focused on applications of RNAi in control of malaria vectors, with life science companies such as Monsanto and Syngenta leading the way in developing RNAi for application in agriculture.
RNAi two ways
Monsanto has made RNAi a research priority since the 1990s, and has successfully applied RNAi technology for virus resistance in papaya and squash. Currently, Monsanto’s next generation corn rootworm product that will ultimately become part of the Smart Stax Pro product is under regulatory evaluation in the U.S. In Canada, a single event using RNAi that will become part of Smart Stax Pro – MON 87411 – is under review with the Canadian Food Inspection Agency (CFIA). Following approval of MON 98411, expected in December 2015, Monsanto will submit the Smart Stax Pro “stack notification” to CFIA.
RNAi can work in two ways for pest control in crops: plants can be genetically modified to “knock down” the expression of a target gene in an insect pest using RNAi, or topical applications of double-stranded RNA (dsRNA) can be administered to the plant exogenously – through a spray, for example.
In Monsanto’s corn rootworm product, a transgene has been introduced that results in the production of dsRNA molecules with a segment of the corn rootworm DvSnf7 gene sequence – genetic material that is present throughout the corn plant’s root tissue, where the rootworm feeds. “The level of dsRNA produced is not high – approximately one microgram DvSn7 dsRNA per kilogram of root tissue, or roughly a billionth of the mass of root tissue,”
explains Greg Heck, weed control team lead for Monsanto’s chemistry technology area.
When rootworm larvae consume the plant tissue, the dsRNA is taken up by the larvae’s gut proteins. “Once in cells the long dsRNA is processed to shorter pieces that are used by proteins to scan other RNAs for matches to the short RNA,” Heck explains. “If an exact match occurs, then the protein machinery cuts the target RNA in two and renders it non-functional.” When all 21 base pairs of the introduced RNA find a match, the worm’s cells begin to treat its own RNA like a virus, cutting it in pieces using a protein called Argonaute. The introduction of dsRNA results in destruction of specific RNA strands needed for normal growth, effectively killing the rootworm within a few days.
“The RNAi function is naturally present in the rootworm cells,” Heck says. “There, it is used to destroy viruses as well as remove the rootworm’s own RNAs that are no longer needed. If specificity were not part of the system, then the cell would mistakenly destroy needed RNAs. By providing the triggering RNAs via a transgene, we can program the cellular RNAi to go after an RNA of our choosing.”
When dsRNA is applied exogenously to a plant through a spray, it works in essentially the same way – target pests take up dsRNA when they feed on plant tissues. Monsanto is currently in the early stages of research and development of topical applications of dsRNA for potatoes, targeting Colorado potato beetle (CPB). “Earlier this year the CPB project advanced to phase 2 of product development,” Heck says.
Topical dsRNA sprays are years away from commercialization, but this approach offers a viable non-GE alternative that may see greater initial consumer acceptance.
Syngenta is also invested in RNAi as part of its portfolio of biocontrols. In 2013, for a price tag of $522 million, Syngenta acquired Devgen, a Belgium-based multinational biotechnology company that pioneered and licensed RNAi in nematodes in the late 1990s.
According to Luc Maertens, Syngenta’s RNAi platform lead based in Belgium, the company’s most advanced RNA-based biocontrol targets CPB in potato. Syngenta is also working on RNAi for soil pests in other crops. “Based on the successes on above ground soil pests, Syngenta has broadened its technology-focus to include soil pests, and finding solutions for scientific hurdles specific for the soil environment,” Maertens says. “That work is currently in an exploratory stage, and our research and development platform makes us uniquely placed to develop it.”
Stewardship is key
Like any pest control method, RNAi needs to be stewarded to ward off the development of resistance in target pest species. “Resistance has developed to major classes of pesticides, and we should not assume that RNAi will be an exception,” Maertens warns. “It is imperative to gain insights into probable resistance mechanisms to RNAi triggers in insects, to monitor possible resistance in the field, and to support the use of the technology with appropriate stewardship requirements.”
RNAi is not designed as a replacement for chemical controls, but rather as a unique mode of action that can help reduce chemical inputs in an integrated pest management system. And like any pest control option, its safety and utility in the long-term depends on careful stewardship.
Monsanto’s Smart Stax Pro product will express Bacillus thuringiensis (Bt) proteins as well as dsRNA designed to silence DvSnv7, and Heck says the combination of traits will mean greater control over the long-term. “Because multiple mechanisms of control are present, this will help to forestall the development of resistance in the corn rootworm population,” he says.
Safety and consumer acceptance
Maertens says one of the benefits of RNA-based biocontrol is that it employs new modes of action, providing a high degree of precision in pest control. It is highly selective for target pests, even between closely related species. “So far, our data has reinforced that it is safe for people, animals, non-targeted insects and the environment, making it a safe biocontrol option,” he says.
“When an insect consumes plant tissue, the dsRNA, applied as a biocontrol, or expressed by the plant, is taken up into the pest’s cells and triggers the RNAi process which stops the synthesis of the one, targeted essential protein in the target pest,” Maertens explains. “The biocontrol does not change, or have any effect on, the DNA of the pest. The process is highly selective for the target protein and pest because it is based on the RNA sequence which is unique for each protein. The pest’s cells start to die before the pest can cause too much damage to the crop.”
“The specificity of RNAi is a benefit,” Heck agrees. “This is considered when choosing a gene sequence for targeting the pest that is not found in non-target species. For example, the rootworm DvSnf7 sequence is not found in humans. Many natural barriers also exist in non-target organisms like fish, birds and mammals that prevent significant uptake from the environment.”
Heck says the specific sequence used in the corn rootworm product has been tested against more than 15 representative species that might encounter the dsRNA in the field, with no impact observed in the tests.
In a talk delivered to the Lower Mainland Horticultural Improvement Association in 2014, Agriculture and Agri-Food Canada (AAFC) researcher Guus Bakkeren outlined some of the potential applications of RNAi technology in agriculture. “An advantage of the RNA silencing technology is that it does not rely on the production of proteins to have an effect, thereby eliminating the chance of possible allergic reactions (in animals or humans),” Bakkeren said.
Bakkeren noted in his presentation there might be some fears that RNA silencing molecules linger in plants intended for consumption. “The human (mammal) gut is a very hostile place for small RNA molecules so these are not likely to survive there to cause unintended (adverse) effects,” he said. “However, more research needs to be done to study such possible effects.”
According to Rempel, early consumer acceptance of the technology will be key in Canada. “Having worked at Monsanto through the release of GMOs, I believe that more than ever there’s a consumer outreach piece,” he says. “Consumers have to feel safe and confident. Some of that is asking, ‘What are the real risks?’ and then understanding that we can’t turn our back on this technology for the wrong reasons.”
Rempel says public dollars should also be invested early on to drive innovation and allow Canada to keep up with its competitors.
“Public scientists working together with private companies can counteract that narrative that farmers are just being led to the trough. It’s a partnership,” he says.
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Atlantic Farm Women's ConferenceFri Apr 28, 2017
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