Rice NAC transcription factor ONAC095 plays opposite roles in drought and cold stress tolerance

Lei Huang, Yongbo Hong, Huijuan Zhang, Dayong Li, Fengming Song

The NAC (NAM, ATAF and CUC) transcriptional factors constitute a large family with more than 150 members in rice and some of them have been demonstrated to play crucial roles in plant abiotic stress response. Here, we report the characterization of a rice stress-responsive NAC gene, ONAC095, and the exploration of its function in drought and cold stress tolerance. Expression of ONAC095 was up-regulated by drought stress and abscisic acid (ABA) but down-regulated by cold stress. ONAC095 protein had transactivation activity and the C2 domain in C-terminal was found to be critical for transactivation activity. Transgenic rice lines with overexpression of ONAC095 (ONAC095-OE) and dominant chimeric repressor-mediated suppression of ONAC095 (ONAC095-SRDX) were generated. The ONAC095-OE plants showed comparable phenotype to wild type under drought and cold stress conditions. However, the ONAC095-SRDX plants displayed an improved drought tolerance but exhibited an attenuated cold tolerance. The ONAC095-SRDX plants had decreased water loss rate, increased proline and soluble sugar contents, and up-regulated expression of drought-responsive genes under drought condition, whereas the ONAC095-SRDX plants accumulated excess reactive oxygen species, increased malondialdehyde content and down-regulated expression of cold-responsive genes under cold condition. Furthermore, ONAC095-SRDX plants showed an increased ABA sensitivity, contained an elevated ABA level, and displayed altered expression of ABA biosynthetic and metabolic genes as well as some ABA signaling-related genes. Functional analyses through dominant chimeric repressor-mediated suppression of ONAC095 demonstrate that ONAC095 plays opposite roles in drought and cold stress tolerance, acting as a negative regulator of drought response but as a positive regulator of cold response in rice.