Characterization of an inositol 1,3,4-trisphosphate 5/6-kinase gene that is essential for drought and salt stress responses in rice
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Drought and salt stresses are major limiting factors for crop production. To identify critical genes for stress resistance in rice (Oryza sativa L.), we screened T-DNA mutants and identified a drought- and salt-hypersensitive mutant dsm3. The mutant phenotype was caused by a T-DNA insertion in a gene encoding a putative inositol 1,3,4-trisphosphate 5/6-kinase previously named OsITPK2 with unknown function. Under drought stress conditions, the mutant had significantly less accumulation of osmolytes such as proline and soluble sugar and showed significantly reduced root volume, spikelet fertility, biomass, and grain yield; however, malondialdehyde level was increased in the mutant. Interestingly, overexpression of DSM3 (OsITPK2) in rice resulted in drought- and salt-hypersensitive phenotypes and physiological changes similar to those in the mutant. Inositol trisphosphate (IP3) level was decreased in the overexpressors under normal condition and drought stress. A few genes related to osmotic adjustment and reactive oxygen species scavenging were down-regulated in the mutant and overexpression lines. The expression level of DSM3 promoter-driven β-glucuronidase (GUS) reporter gene in rice was induced by drought, salt and abscisic acid. Protoplast transient expression assay indicated that DSM3 is an endoplasmic reticulum protein. Sequence analysis revealed six putative ITPKs in rice. Transcript level analysis of OsITPK genes revealed that they had different tempo-spatial expression patterns, and the responses of DSM3 to abiotic stresses, including drought, salinity, cold, and high temperature, were distinct from the other five members in rice. These results together suggest that DSM3/OsITPK2 is an important member of the OsITPK family for stress responses, and an optimal expression level is essential for drought and salt tolerance in rice.
KeywordsAbiotic stress Inositol phosphate Oryza IP3 Secondary signaling
We thank Changyin Wu and (Huazhong Agricultural University, Wuhan, China) for providing the mutant dsm3, and Jan Xu and Rongjian Ye (Huazhong Agricultural University) for providing plasmid pM999-33 and DX2181, respectively. We also thank Yihua Zhou (Institute of Genetics and Development, Chinese Academy Science) for providing endoplasmic reticulum marker in subcellular localization assays. This work was supported by grants from the National Natural Science Foundation of China (30725021, 30921091, and 30830071), the National Program on the Development of Basic Research (2012CB114305), and the Project from the Ministry of Agriculture of China for Transgenic Research.
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