- Daniel Nelson, scidev.net, August 20, 2009
In a letter published in Nature today (20 August), a team of Japanese researchers led by Motoyuki Ashikari, a professor at the Bioscience and Biotechnology Center at Nagoya University, say they have identified two genes that allow deep-water varieties to elongate their stems as water rises, helping the plant keep its leaves above water.
Importing the genes 'SNORKEL1' and 'SNORKEL2' into varieties that do not usually survive in deep water stopped the plants drowning. Once under water, their adopted genes switched on the process by which the stems became elongated.
Ashikari told SciDev.Net that the two genes and their molecular mechanism were previously unknown. He says he hopes that the team's work will help increase production in flood-prone areas, and that he is now aiming to develop new, high-yielding varieties with deep-water characteristics.
Thirteen years ago, David Mackill, now head of the plant breeding, genetics and biotechnology division of the International Rice Research Institute (IRRI) in the Philippines, and his then graduate student Xu Kenong announced the discovery of a gene, Sub 1A, that allowed an Indian variety to survive submersion for more than two weeks.
Last December, researchers said that the rice, known as 'scuba' rice, had passed its field tests with "flying colours" (see Waterproof rice passes international field tests). Ashikari says that Sub1A is effective for short periods of flooding, but SNORKEL1 and SNORKEL2 function in heavy, long-duration floods.
Laurentius Voesenek of Utrecht University in the Netherlands, who wrote a commentary on the findings in Nature, says that both the Sub1A and SNORKEL genes are regulated by accumulated ethylene inside the submerged plant.
"Many relevant crop species are very intolerant to water-saturated growth conditions," he says.
"During selection for yield, traits related to flooding tolerance are largely lost in these crops. Very often, wild relatives still contain these genes. They should be identified and subsequently introduced in good yielding cultivars."
About 30 per cent of rice acreage in Asia and 40 per cent in Africa are rain-fed paddies exposed to fluctuating water levels. Sophie Clayton of IRRI told SciDev.Net that Bangladesh and India are the countries with most to gain from flood-tolerant rice. She pointed out that in the Philippines alone, around 370,000 hectares of rice-growing land experiences flooding, causing average crop losses of about 250,000 tonnes every year.
Plant biology: Genetics of high-rise rice
- Laurentius A. C. J. Voesenek & Julia Bailey-Serres, Nature 460, 959-960 (20 August 2009)
When subject to flooding, deepwater rice survives by shooting up in height. Knowledge of the genetic context of this and other responses to inundation will be a boon in enhancing rice productivity.
Plant biologyGenetics of high-rise rice
Deepwater rice lives up to its name: this variety can outgrow slowly rising floodwaters of up to 4 metres in depth. On page 1026 of this issue, Hattori and colleagues1 describe how they have identified two genes, SNORKEL1 and SNORKEL2, that contribute to this spectacular elongation response.
Rice — the seed of Oryza sativa — feeds billions. Although productivity per hectare has more than doubled since the 1960s, a further doubling will be necessary to meet projected requirements by 2050 (refs 2, 3). More than 30% of Asian and 40% of African rice acreage is cultivated in either lowland paddies (15–50 centimetres deep) or deepwater paddies (depth of more than 50 cm). But lack of control of water depth in rain-fed paddies can be a serious problem: in some areas, water levels rise progressively during the growing season and can reach several metres; in others, flash flooding can fully submerge plants for days or weeks. High-yielding rice varieties cannot survive either extreme of inundation. As a result, some flood-prone areas are planted with traditional local varieties that display a remarkable capacity for flooding-induced elongation — of up to 25 cm per day — or that can tolerate submergence for up to 15 days. But the high-yielding varieties are typically five times more productive than these flood-tolerant plants
full paper at
'Snorkel' Genes Help Stop Rice Drowning
News Aug 24, 2009