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PNAS 103 (35), 12987-12992 (2006) | Abs | CrossRef
doi: 10.1073/pnas.0604882103
Published online August 21, 2006, PNAS Press August 29,2006

Better to close some windows 

Rice (Asia: Oryza sativa L. & Africa: Oryza glaberrima Steud) is a model genome for one of the two main groups of flowering plants, the monocotyledons, in the same way as Arabidopsis thaliana is the model for the other group, the dicotyledons. Now it needs no any word to say again the importance of the rice. As the primary source of the food for more than half of humanity, scientists have paid much attention to increase its yield with limited land, and try to transfer new advantageous varieties adapted to different cultivated conditions, for example, create new transgenic varieties which are resistant to disease, pests, flooded or drought, salinity, or low/high temperature and so on.

After tedious hard work, HU Hong-hong, XIONG Li-zhong and their colleagues from National Key Laboratory of Crop Genetic Improvement, National Center of Plant Gene Research and Huazhong Agricultural University in Wuhan, China, described new transgenic rice in August 2006 in PNAS. They encoded the rice with powerful potential in regulating stomatal movement. By overexpressing of the stress responsive gene SNAC1 (STRESS-RESPONSIVE NAC 1) which is induced predominantly in guard cells by drought and encodes a NAM, ATAF, and CUC (NAC) transcription factor with transactivation activity, the rice was significantly resistant to severe drought and salinity under practical field test.

This study provides alternative pathway for regulating stomatal closure of the rice's leaves, which is triggered by the strongly localized induction of SNAC1 in guard cells. They elucidated that this transgenic rice without phenotypic changes was more sensitive to abscisic acid and lost water more slowly by closing more stomata, yet showed no significant difference in the rate of photosynthesis, thus no yield penalty.

fit survival 2006
Credit: Scidea Art 2006. Source: ScideaNews.com

This finding is somewhat surprise but is certainly an interesting take on the situation. The authors speculate that the rice leaves function normally with more open stomata than may be optimal. It's reasonable. They also pointed that, among the genes up-regulated in the SNAC1-overexpressing transgenic plants, no gene was found to have homology to transporter or antiporter genes that were previously reported to function in salt tolerance, indicating that there was another potential mechanism of salt tolerance regulated by SNAC1. Upon these points, I guess that the enhanced salt tolerance may be attributed to the mechanical reason rather than directly regulating by certain gene, that is, low transpiration rate due to more closed stomata would decrease the adsorbing level of the salt water in rice root.

Although the evidence showed that there was no tested yield penalty for this new transgenic rice, the transfer of advantageous traits to locally adapted varieties is much more important.

 * Lin Pu is in the Physics Department of Nanjing University, Nanjing 210093, CHINA.

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