The abiotic stress-responsive NAC-type transcription factor OsNAC5 regulates stress-inducible genes and stress tolerance in rice.

The transcription factor OsNAC5 in rice is a member of the plant-specific NAC family that regulates stress responses. Expression of OsNAC5 is induced by abiotic stresses such as drought, cold, high salinity, abscisic acid and methyl jasmonic acid. Transactivation assays using rice protoplasts demonstrated that OsNAC5 is a transcriptional activator, and subcellular localization studies using OsNAC5-GFP fusion proteins showed that it is localized to the nucleus. Pull-down assays revealed that OsNAC5 interacts with OsNAC5, OsNAC6 and SNAC1. To analyze the function of OsNAC5 in rice plants, we generated transgenic plants that overexpressed OsNAC5. The growth of these plants was similar to that of control plants, whereas the growth of OsNAC6-overexpressing transgenic plants was retarded. OsNAC5-overexpressing transgenic plants also had improved tolerance to high salinity compared to control plants. By microarray analysis, many stress-inducible genes, including the "late embryogenesis abundant" gene OsLEA3, were upregulated in rice plants that overexpressed OsNAC5. By gel mobility shift assay, OsNAC5 and OsNAC6 were shown to bind to the OsLEA3 promoter. Collectively, our results indicate that the stress-responsive proteins OsNAC5 and OsNAC6 are transcriptional activators that enhance stress tolerance by upregulating the expression of stress-inducible rice genes such as OsLEA3, although the effects of these proteins on growth are different. Furthermore, because OsNAC5 overexpression did not retard growth, OsNAC5 may be a useful gene that can improve the stress tolerance of rice without affecting its growth.