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Snorkel Genes to the Rescue

19 August 2009 (All day)
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Motoyuki Ashikari

Tall tale. During a flood, this deep-water rice variety grew more than 5 meters high.

Japanese researchers have discovered a genetic life preserver for drowning rice. Two genes--appropriately named SNORKEL1 and SNORKEL2--help certain varieties of the crop stretch their stems above inundating water, allowing the plant to continue breathing. The team also showed that the genes can be bred into other rice varieties, which could resist devastating floods.

Plants are just like us: They can drown if they spend too long underwater. Some varieties of rice tackle the problem with a "submergence" gene, which gets them through short floods by suppressing growth. More dramatically, "deep water" rice varieties can extend their normally centimeters-long stems up to 4 meters or more as water rises, keeping the tip of the stem, rice flowers, and topmost leaves above water (see video). Like a snorkel, the stem carries oxygen through its porous center, down into the plant to keep the roots and leaves alive.

To find the genes responsible for the stem-lengthening, plant molecular geneticist Motoyuki Ashikari of Nagoya University and colleagues compared two varieties of rice, one that shoots up when submerged and one that doesn't. The researchers crossed the plants and examined their descendants to see which ones grew long stems in water and how long the stems grew. Then they used molecular markers to pinpoint two genes on chromosome 12 that seemed to be key to stem lengthening and named them SNORKEL1 and SNORKEL2. To confirm the genes' function, the researchers bred plants containing SNORKEL1 and SNORKEL2 with a variety of rice that doesn't normally elongate in floods--and indeed, the offspring picked up the ability to grow tall in floodwater, the team reports tomorrow in Nature.

The next step, says Ashikari, is to use this new genetic knowledge to breed rice that is both high-yielding and flood-resistant. This would be especially useful in flood-prone places like Bangladesh, where, during the rainy season, farmers currently plant deep-water rice varieties that don't produce much grain.

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Flood zone. Deep-water rice (right) elongates day by day as the water level rises, while normal rice (left) drowns.
Credit: Motoyuki Ashikari

Molecular geneticist Julia Bailey-Serres of the University of California, Riverside, is enthusiastic about Ashikari's research. She helped develop rice with the submergence gene and says it will be great to be able to provide poor farmers with a rice variety suited to a different pattern of flooding.

Ashikari estimates that flood-friendly rice could be in farmers' fields in 3 or 4 years. He would also like to find genes for other rice traits, like the ability to survive in salty water, which could be useful in fields that occasionally get flooded by ocean waters. Whatever is developed, Ashikari says, taste is critical: "I want to ask someone if my rice is good or not."