Water thermostat could help engineer drought resistant crops

Duke University researchers have
identified a gene that could help scientists engineer
drought-resistant crops. The gene, called OSCA1, encodes
a protein in the cell membrane of plants that senses
changes in water availability and adjusts the plant's water
conservation machinery accordingly.
"It's similar to a thermostat," said Zhen-Ming Pei, an
associate professor of biology at Duke.
The findings, which appear Aug. 28 in the journal Nature,
could make it easier to feed the world's growing population
in the face of climate change.
Drought is the major cause of crop losses worldwide. A dry
spell at a crucial stage of the growing season can cut some
crop yields in half.
Water shortages are expected to become more frequent and
severe if climate change makes rainfall patterns
increasingly unreliable and farmland in some regions
continues to dry up. Coupled with a world population that is
expected to increase by two billion to three billion by 2050,
researchers worldwide are looking for ways to produce
more food with less water.
Some researchers hope that genetic engineering -- in
addition to improved farming practices and traditional plant
breeding –- will add to the arsenal of techniques to help
crops withstand summer's swelter. But engineering plants
to withstand drought has proven difficult to do, largely
because plants use so many strategies to deal with
dehydration and hundreds of genes are involved.
The problem is confounded by the fact that drought is often
accompanied by heat waves and other stresses that require
different coping strategies on the part of the plant, Pei said.
One way that plants respond to water loss is by boosting
the levels of calcium within their cells. The calcium surge
acts as an alarm signal that triggers coping mechanisms to
help the plant rebalance its water budget. But until now, the
molecular machinery that plants use to send this signal –-
and monitor water availability in general -- remained
unknown.
Pei and Duke colleagues Fang Yuan, James Siedow and
others identified a gene that encodes a protein in the cell
membranes of plant leaves and roots, called OSCA1, which
acts as a channel that allows calcium to surge into the cell
in times of drought.
The gene was identified in Arabidopsis thaliana, a small
unassuming plant related to cabbage and canola that is the
lab rat of plant research.
Plants with defective versions of the calcium channel don't
send an alarm signal under water stress like normal plants
do.
When the researchers grew normal plants and plants with
defective versions of the gene side by side in the same pot
and exposed them to drought stress, the mutant plants
experienced more wilting.
The findings could lead to new ways to help plants thrive
when water is scarce.
The team's next step is to manipulate the activity of the
OSCA1 gene and related genes and see how those plants
respond to drought –- information that could lead to crops
that respond more quickly and efficiently to dehydration.
"Plants that enter drought-fighting mode quickly and then
switch back to normal growth mode quickly when drought
stress is gone should be able to allocate energy more
efficiently toward growth," Pei said.