Biologists at the University of California, San Diego have identified genes in a laboratory weed that are necessary for normal seed dispersal.
In the April 14th issue of Nature, the researchers report the identification of two genes in Arabidopsis that, when inactivated, prevent this weed from shattering its seed-containing pods. This is significant because the inactivation of these same genes in canola and other closely related, commercially important crops should prevent the premature dispersal of seeds that typically results in significant losses of yield.
The discovery could dramatically increase the harvesting of canola seeds, a $9-billion-a-year industry worldwide that is rapidly growing because of the health benefits of canola oil, but is now hampered because so much of that crop is lost to pod shatter. It could also lead to commercially significant savings in the collection of seeds for valuable hybrids of broccoli, cauliflower and other crops.
"Under adverse conditions, such as very windy conditions, which is not all that uncommon during the harvesting time, as much as half of the canola crop ends up on the ground," says Martin F. Yanofsky, a professor of biology at UCSD who headed the research team that made the discovery. "If you can double the yield, that means you can plant the canola on half as much land and use half as much of the chemical fertilizers and pesticides that are now routinely sprayed on these plants."
In their study, UCSD biologists Sarah J. Liljegren, Gary S. Ditta, and Yanofsky identified a type of gene, called a "shatterproof" gene, that allows Arabidopsis plants to disperse their seeds. Two other scientists from the University of California, Davis, John L. Bowman and Yuval Eshed, and a former UCSD scientist, Beth Savidge, contributed to the study. The UCSD scientists determined that mutant strains without two normal copies of this type of gene, lacked the ability to disperse seeds through pod shatter.
"These two genes are what we call functionally redundant," explains Yanofsky, "meaning that they are so similar to one another that the proteins they produce are virtually identical. Knocking out just one gene leaves the pod-shattering mechanism intact. So in order to identify the shatterproof function, we had to knock out both genes. Only when we had the double mutant did we actually get the effect."
The UCSD researchers believe that the shatterproof genes in Arabidopsis are the identical genes used by canola, broccoli, brussels sprouts, and others in the Brassica family of mustard plants to promote seed dispersal.
"Most people don't realize this, but when broccoli and cauliflower do go on to flower, they will produce fruit that looks exactly the same as the fruit of Aribidopsis, " says Yanofsky. "The fruit of Aribidopsis is much smaller, but morphologically, the overall structure of the pod, its architecture, how it develops and the genes that are involved are the same in all of these plants. So we should be able to control this process in each of these plants."
The UCSD researchers believe the applications of this discovery to agriculture should come quickly, because knocking out the genes in all of these plants is now a relatively straight-forward process. One agricultural biotechnology company is already working with the UCSD researchers to prevent pod shatter in canola.
"Although these plants are grown to eat or for the oils they produce," notes Yanofsky, "they're also grown to make seeds for the next generation of crops. There's a lot of time and money that goes into producing the seeds. So any increase in the yield of the seeds will be beneficial."
The largest commercial impact of the discovery, however, will be in the canola-seed production industry. Because the valuable canola oils begin to accumulate in the seeds just as the plants approach maturity, farmers usually wait until their crop is fully mature before they begin harvesting the seeds.
"Typically, the pods are opening at the same time the farmers are collecting the canola seeds, so its essentially a race in which the farmers try to get as much of their crop without losing it to this pod-shattering problem," says Yanofsky. "By knocking out the two shatterproof genes, we can eliminate this problem, while drastically increasing the yield of canola and perhaps even doubling it."
The study was supported by grants from the National Science Foundation, the National Institutes of Health, the Monsanto Company and the University of California's BioSTAR program.