Nearly every year, seasonal flash floods drown a quarter of the world's rice crops, resulting in more than a billion dollars in lost revenue. Farmers have tried to fight back by selectively breeding the plants to better withstand submersion, but they've met with limited success. Now scientists report a breakthrough in "waterproofing" rice: the discovery of a cluster of genes that allows plants to survive submersion.
Submerged plants have a hard time absorbing carbon dioxide and oxygen, and as a result, they have trouble converting the sun's energy into food via photosynthesis. Farmers have long noticed that some plants seem to fare much better in wet conditions than do others. But these crops tend to have low yields and poor grain quality, says geneticist Pamela Ronald of the University of California, Davis, and breeding these plants without knowing what genes to extract is time consuming and inefficient.
So Ronald and her team set out to identify the specific genes that allow some plants to weather the storm. By comparing the genomes of flood-tolerant plants, the researchers were able to pin down the resistance to a particular region of the plant genome, which they dubbed Submergence 2. Two genes in this region changed their expression patterns when submerged, and one of these, called Sub1A-1, could turn submergence-intolerant plants into flood survivors when artificially inserted into the genome. Ronald suspects that the transplanted genes enable plants to cope with limited gas exchange by slowing their metabolism. "It's almost like they hold their breath under the water," she says.
Armed with the new knowledge, the researchers were able to breed submergence-resistant plants that still produced decent rice yields, the team reports 10 August in Nature. The researchers are currently distributing the new rice varieties to programs in India and Bangladesh, where the transgenic plants will be tested to ensure that, aside from their flood resistance, they have no other side effects.
The work represents "a really nice collaboration between molecular biologists and plant breeders," says Jan Leach, a plant pathologist at Colorado State University in Fort Collins. The finding of submergence-specific genes should greatly accelerate the pace of breeding optimal rice crops, he says.