|April 13, 2000
Media Contact: Kim
McDonald (858) 534-7572
of Arabidopsis fruit undergoing seed dispersal.
Photo Credit: Sarah Liljegren, UCSD
UCSD SCIENTISTS IDENTIFY GENES
CONTROLLING SEED DISPERSAL
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
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