Sci. Signal., 25 August 2009
Plant Biology SNORKELing for Rice
Science Signaling, AAAS, Washington, DC 20005, USA
The seed of Oryza sativa, more commonly known as rice, is an important food crop. Many areas that depend on rice cultivation are subject to flooding, an environmental condition that usually drowns high-yield rice varieties. Deepwater rice varieties can survive submersion by rapidly lengthening their internodes (the hollow portions of the stems between the nodes) to allow above-water gas exchange but generally do not produce high yields. Hattori et al. previously identified quantitative trait loci (QTL) on chromosomes 1, 3, and 12 that mediate internode elongation in deepwater rice; of these, the QTL on chromosome 12 had the greatest effect. The authors (see also Voesenek and Bailey-Serres) identified SNORKEL1 (SK1) and SK2 genes on chromosome 12 that were present in the deepwater rice variety C9285 but not in a nondeepwater rice variety (T65). The SK genes contained an ethylene response factor domain, and the proteins encoded by these genes localized to the nucleus and displayed transcriptional activity. The expression of the SK genes increased in C9285 under deep water compared with dry conditions and was induced by application of ethylene, but not other hormones, including gibberellin or auxin. In addition, ethylene treatment triggered internode elongation in C9285 but not T65, an effect that was reduced in C9285 by the ethylene inhibitor 1-methylcyclopropene. Deepwater conditions promoted the accumulation of ethylene in both C9285 and T65, indicating that ethylene accumulation during submersion was due to environmental (the low diffusion rate of ethylene in water) rather than genetic factors. However, concentrations of gibberellin, a hormone that promotes plant growth, increased under deepwater conditions in C9285 but not T65, and the gibberellin inhibitor uniconazole blocked internode elongation in submerged C9285 plants, suggesting that gibberellin signaling may function downstream of ethylene signaling in the deepwater response. Wild rice species are the progenitors of O. sativa, and a variety that may be adapted for dry areas expressed a truncated form of SK2, in contrast to two varieties that grow in wet areas and express full-length SK2, suggesting that SK2 may be more critical than SK1 for the deepwater response. QTL from chromosomes 1, 3, and 12 of C9285 were introduced into T65; this line exhibited greater internodal elongation under deepwater conditions compared with the parental T65. Thus, these genetic analyses provide a way to improve the tolerance of high-yield varieties to flooding.
Y. Hattori, K. Nagai, S. Furukawa, X.-J. Song, R. Kawano, H. Sakakibara, J. Wu, T. Matsumoto, A. Yoshimura, H. Kitano, M. Matsuoka, H. Mori, M. Ashikari, The ethylene response factors SNORKEL1 and SNORKEL2 allow rice to adapt to deep water. Nature 460, 1026–1030 (2009). [Online Journal]
L. A. C. J. Voesenek, J. Bailey-Serres, Plant biology: Genetics of high-rise rice. Nature 460, 959–960 (2009). [Online Journal]
Citation: W. Wong, SNORKELing for Rice. Sci. Signal. 2, ec282 (2009).
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