Wheat and other edible grasses have developed pores that make them more drought tolerant. Stanford scientists have studied these pores with an eye toward future climate change.
These plants, which make up about 60 percent of the calories people consume worldwide, have a modified stoma that experts believe makes them better able to withstand drought or high temperatures. Stanford University scientists have now confirmed the increased efficiency of grass stomata and gained insight into how they develop. Their findings, reported in the March 17 issue of Science, could help us cultivate crops that can thrive in a changing climate.
“Ultimately, we have to feed people,” said Dominique Bergmann, professor of biology and senior author of the paper. “The climate is changing and, regardless of the cause, we’re still relying on plants to be able to survive whatever climate we do have.”
Adjusting an ancient system
Grasses – which include wheat, corn and rice – developed different stomata, which may have helped them spread during a prehistoric period of increased global dryness. Stomata usually have two so-called “guard cells” with a hole in the middle that opens and closes depending on how a plant needs to balance its gas exchange. If a plant needs more CO2 or wants to cool by releasing water vapour, the stomata open. If it needs to conserve water, they stay closed.
The protein in yellow moves out of the guard cells into cells on both sides. By recruiting these cells, grass stomata become better suited to hot and dry environments.
Grasses improved on the original structure by recruiting two extra cells on either side of the guard cells, allowing for a little extra give when the stoma opens. They also respond more rapidly and sensitively to changes in light, temperature or humidity that happen during the day. Scientists hope that by knowing more about how grass developed this system, they may be able to create or select for edible plants that can withstand dry and hot environments, which are likely to become more prevalent as our climate changes.
“We take our food and agriculture for granted. It’s not something the ‘first world’ has to deal with, but there are still large areas of the world that suffer from famine and this will increase,” said Michael Raissig, a postdoctoral researcher in the Bergmann lab and lead author of the paper. “The human population is going to explode in the next 20 to 30 years and most of that is in the developing world. That’s also where climate change will have the biggest effect.”
Growing a better mouth
Scientists have assumed grasses’ unusual stomata make these plants more efficient “breathers.” But, spurred by curiosity and a passion for developmental biology, these researchers decided to test that theory.
Thanks to a bit of luck, they found a mutant of the wheat relative Brachypodium distachyon that had two-celled stomata. Partnering with the Berry lab at the Carnegie Institution for Science, the group compared the stomata from the mutant to the normal four-celled stomata. They not only confirmed that the four-celled version opens wider and faster but also identified which gene creates the four-celled stomata – but it wasn’t a gene they expected.
“Because it was a grass-specific cell-type, we thought it would be a grass-specific factor as well,” said Raissig, “but it’s not.”
Instead of relying on a completely new mechanism, the recruitment of the extra cells seems to be controlled by a well-studied factor which is known to switch other genes on and off. In other plants, that factor is present in guard cells, where it is involved in their development. In grasses, the team found that the factor migrated out of guard cells and directly into two surrounding cells, recruiting them to form the four-celled stomata.
Feeding the world
Over evolutionary time, humans have bred and propagated plants that produce the kinds of foods we like and that can survive extreme weather.
“We’re not consciously breeding for stomata but we’re unconsciously selecting for them,” said Bergmann, who is also a Howard Hughes Medical Institute investigator. “When we want something that’s more drought resistant, or something that can work better in higher temperatures, or something that is just able to take in carbon better, often what we are actually doing is selecting for various properties of stomata.”
The adaptability and productivity of grass makes understanding this plant family critical for human survival, the scientists said. Someday, whether through genetic modification or selective breeding, scientists might be able to use these findings to produce other plants with four-celled stomata. This could also be one of many changes – to chloroplasts or enzymes, for example – that help plants photosynthesize more efficiently to feed a growing population.
Annually, diseases, weeds, and insects are estimated to cause more than $1.3 billion in losses for sunflower growers. To combat this, researchers are preserving the genetic diversity of wild sunflowers. Wild plants retain the genes needed to resist pests and survive in different environments.
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.
Some scientists say the solution could lie in crops' DNA and are making “gene catalogs” to help farmers grow healthier produce that can withstand climate change. | READ MORE
New South Wales (Australia) Department of Primary Industries senior principal research scientist, Harsh Raman, said the study has unlocked the genetic make-up of canola to characterize major and minor genes resistant to the fungal pathogen Leptosphaeria maculans, which causes blackleg disease. | READ MORE
Plant geneticist Harold Trick said the university has received a patent for the technology that “silences” specific genes in the nematode, causing it to die or, at the least, lose the ability to reproduce.
“We have created genetically engineered vectors [or DNA molecules], and put those into soybeans so that when the nematodes feed on the roots of the soybeans, they ingest these small molecules,” said Trick, who has worked closely with plant pathologist Tim Todd on this project.
So far, the scientists have found the technology has reduced the nematode population in greenhouse studies by as much as 85 percent. | READ MORE
As a postdoc at the University of Guelph’s College of Biological Science, Liu had been working on a project transforming starch branching enzymes (SBEs) from maize into arabidopsis plants. For weeks, he’d been analyzing the interesting effects of the maize SBEs on the arabidopsis plants’ starch pathways. Then one day he realized the plants he’d been working on had grown much larger than the control plants. Not only that, but there were also far more seedpods, and their leaf and root systems were bigger, too.
“That was the beginning – I saw a really big arabidopsis plant and thought, let’s take a picture. Something has happened biologically,” Liu says.
He showed the photo to his supervisors, Guelph professors Michael Emes and Ian Tetlow.
“We’d found some interesting effects on the starch, and had done all sorts of measurements,” Emes echoes. “And then one day we stood back and looked at the plants, and we finally saw the wood for the trees. We saw these plants were really different.”
A healthy plant from a typical arabidopsis line normally bears about 11,000 seeds; the new plants bore 50,000 seeds per plant – a more than 400-per-cent increase in seed production.
“The plants were bigger, the leaves were bigger, there were more stems, there was more flowering and more seed,” Emes says. “It’s not just that there were a lot more seeds, there was a lot more of everything.
“It was one of those serendipitous events in science. If you’d asked me to produce a plant with more seeds I would have said you couldn’t get there from here,” he adds.
Liu’s focus had been on trying to analyze how the SBEs’ functions changed in arabidopsis leaves, but after this discovery his focus changed to studying the impact on seed yield and biomass, comparing transformed plants with wild-type arabidopsis plants. Importantly, the quality of the oil remained the same as for the non-transgenic plants.
The team published their findings this spring in the Arabidopsis is not a starch crop, but an oilseed genetically similar to canola, so the obvious application of the finding is in breeding higher-yielding oilseed crops for biofuels. Emes and Tetlow have already begun preliminary work with canola, but also foresee potential applications in camelina, soybeans and other crops.
While the dramatic increase in seed production might not occur as easily in canola as in arabidopsis, Liu says even a tenth of the effect would still mean an increase of 40 per cent – a substantial impact on yield.
“This is orders of magnitude different than conventional breeding,” Emes says.
But what, exactly, is going on in the plants?
The good times are here
Emes has a theory that the starch metabolism in the transformants has improved the plants’ ability to grow and reproduce.
The team is working on two lines using two starch genes from maize. In one of the new lines, there is a massive increase of starch in the leaves, which the plant breaks down overnight. In the other line, there is a bigger impact on yield; there is still an increase in starch in the leaves, but it doesn’t all break down at night, leaving a carbohydrate reserve.
“We know that carbohydrates, during seed development, come from the leaf through the vascular system and into the reproductive system. These are important to flower development and what’s called embryo abortion – the plant makes a kind of ‘decision’ on whether or not to produce seeds,” Emes explains. “Flower and seed production is limited by the supply of carbohydrates. So these plants are now saying, ‘The good times are here, let’s go for it.’ ”
Emes suspects that the wild type arabidopsis plant has an endogenous mechanism that constrains growth because it’s genetically evolved to always keep something in reserve. But in the transgenic plants, the brakes have been taken off.
If the scientists can crack the code on the maize SBEs’ effect on oilseeds, Emes sees potential applications for feedstock and oil for human consumption, as well as biofuels. He is currently seeking public and private funding to continue the project in canola.
Liu, now a regulatory scientist for the J.R. Simplot Company, says much more work is required to improve seed quality as well as yield in future breeding projects. “If you want to improve quality, if you want to improve omega-3 fatty acid or other special fatty acid content, for now I don’t have any insight on how you can improve those things, from this study,” he says. “At least, from the analysis of the arabidopsis you don’t see a change in these properties – you just get higher yields.”
But Liu is optimistic about the future applications of his work. “Genes are so powerful,” he says. “One small change could be a potential opportunity for dramatically improving crops.”
The technology is incredibly, and increasingly, valuable to Eastern Canadian growers, where 2,035,000 of the total 2,295,000 acres of corn were planted to Bt hybrids in 2015. But the ever-present risk of the development of insect resistance to the technology is keeping the industry on its toes.
While resistance hasn’t yet developed in European corn borer (ECB) populations in North America, reduced susceptibility has been noted in some populations of corn rootworm, according to Jocelyn Smith, a research associate in field crop pest management at the University of Guelph’s Ridgetown Campus.
But resistance can be delayed with proper management. In Canada, stewardship of Bt technology takes the form of insect resistance management (IRM) plans, which chiefly involve maintaining refuges to delay the development of resistant insect populations.
Stewardship also entails rotation of traits in the field, as well as the use of stacked traits.
“The most important thing we can do with this issue is educate growers more about the risks they’re taking if they continuously use traits for rootworm,” Smith says. “Their sheer numbers and biology give them advantage.”
This is a message familiar to Eastern Canadian corn producers, and they’ve taken it to heart. The Canadian Corn Pest Coalition (CCPC) – made up of academics (such as University of Guelph researchers), the Canadian Food Inspection Agency (CFIA), the provincial ministries of agriculture, and industry representatives – has been conducting surveys on insect resistance management compliance since the late 1990s.
Until 2012, those surveys were conducted in alternating years with CFIA IRM compliance surveys, but that year, stewardship compliance rates were so high CFIA discontinued them unless “in future, industry practice shifts from using blended refuge.”
But the CCPC’s bi-annual survey continues. “The increase in compliance with refuge area requirements from 2013 to 2015 occurred in all three provinces and now stands at 91 per cent in Ontario, 90 per cent in Quebec and 91 per cent in Manitoba,” the 2015 report concluded.
According to the same report, compliance tended to be higher in the 35 to 44 age category, but lower among producers who believed stewardship requirements to be “only somewhat important.” In addition, the report indicates awareness of stewardship requirements has declined since 2013, particularly in Ontario; compliance was also lower among those who believed they did not understand requirements.
More education needed
Cindy Pearson, national manager of the CFIA’s Plant Biosafety Office, says the onus is on companies marketing Bt products to educate producers regarding the need for delaying resistance and how refuges work.
“IRM plans are the responsibility of the company to whom the Bt corn product has been authorized, and CFIA receives specific reports from companies that
detail their various activities on that front,” Pearson says.
The survey notes refuge-in-a-bag (RIB) hybrids, which contain the required percentage of refuge seed, resulted in significantly higher compliance rates after their market introduction several years ago. The market has also changed with the introduction of stacked hybrids with multiple Bt traits or modes of action against the insect pests.
“There are currently three traits available for corn rootworm control,” she says. “Where we have growers with long-term use of two of those traits on their own (not in a stacked product), we’ve started to
notice some shifts in susceptibility when we test those populations in the lab.”
This doesn’t necessarily mean producers can see resistance developing in the field, but it’s still a red flag.
“We need to focus on informing continuous corn growers that the three-year limit is important,” Smith says. “We may have had a situation where a grower has used a single trait for years and it’s compromised, so then when they use the stack there’s only one viable trait remaining against the pest.”
Smith also emphasizes monitoring as a key aspect of stewardship. “If you are growing corn on corn, scout your corn late in the season and if there’s less than one beetle per plant you might be able to get away without using transgenics,” she says. “You might be able to hold off on using some of the technology in the following year.”
Smith also recommends rotating management options — in other words, soil insecticides and Bt traits.
“And again in season, keep an eye on the pest situation in the crop. For ECB and rootworm, you need to monitor whether they are being controlled by the Bt hybrids or not. If they are not, you need to notify the CCPC and the trait provider,” she says.
As long as they use Bt technology, producers are on notice to use it well. Resistance is in nobody’s interest except the insects.
Shallow banding N risks volatilization lossWhat would the late John Harapiak think of this: Nitrogen…
Organic farming not always best for the planetMany consumers think organic is better for humans and the…
New pea processing plant to be built near Portage la Prairie, M.B.A new $400 million pea processing plant is in the…
Banking on edible dry beansWhen Meghan Moran, the canola and edible bean specialist for…
Royal Manitoba Winter FairMon Mar 27, 2017
Employee Selection WebinarMon Mar 27, 2017 @10:00am -
Cultivating the Great Clay Belt Agriculture SymposiumThu Mar 30, 2017
Hiring Employees WebinarMon Apr 03, 2017 @10:00am -
Spring Workshop on Organic ResearchFri Apr 07, 2017 @ 8:30am - 04:00pm