Transcriptional profiling revealed that a relative large portion of the Arabidopsis and rice NAC TF families exhibited differential expression patterns in response to various biotic and abiotic stresses. Beside the involvement in growth and development, the function of the NAC TFs in biotic and abiotic stress responses has been well documented in both model and crop plants. The NAC TFs contain a highly conserved NAC domain at N-terminal, which determines DNA-binding activity, and a variable domain at C-terminal, which is responsible for transcription activity. NAC proteins are plant-specific TFs and constitute a large family with 151 members in rice. It was also suggested that some of the functionally characterized TF genes may have great potentials in improvement of abiotic stress tolerance in crop plants. Genetic and molecular studies using knockout/knockdown mutants and/or overexpression lines have revealed that many families of TFs such as NAC, AP2/ERF, MYB, WRKY, bZIP, homeodomain, bHLH, NF-Y and CAMTA have members that play roles in abiotic stress response. Such large proportion of differentially expressed genes during a specific abiotic stress response requires a synergistic action of different types of transcription factors (TFs) in both temporal and spatial manners. For example, a total of 5866 genes (2145 up-regulated and 3721 down-regulated), accounting for ~18 % of the annotated genes in rice genome, were differentially expressed during drought stress in rice. Upon perception of environmental stimuli, stress-initiated signaling network often effectively and timely reprograms the expression of a large spectrum of stress-responsive genes. In addition, stress-induced reactive oxygen species (ROS), including hydrogen peroxide (H 2O 2) and superoxide anion, are harmful by-products causing cellular oxidative damage at excess level, whereas ROS are also considered to play signaling roles in regulating abiotic stress response at proper cellular concentration. A number of key genes that are involved in the ABA-dependent and ABA-independent stress pathways have been identified, including DRE-binding protein/C-repeat-binding factor (CBF), ABA-binding factor, MYC and MYB. Abscisic acid (ABA), as a critical stress phytohormone, plays important roles in abiotic stress signaling networks, and the ABA-mediated stress signaling can be divided into ABA-dependent and ABA-independent pathways. Extensive studies have revealed that plants can timely sense external signals and initiate effectively complicated signaling networks to respond to environmental stress by activating various cellular, physiological, biochemical and metabolic processes. Conclusionįunctional 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.Įnvironmental constraints such as drought, salt and extreme temperatures often affect adversely plant growth and development, which lead to great loss of productivity worldwide. 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. 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. However, the ONAC095-SRDX plants displayed an improved drought tolerance but exhibited an attenuated cold tolerance. The ONAC095-OE plants showed comparable phenotype to wild type under drought and cold stress conditions. Transgenic rice lines with overexpression of ONAC095 (ONAC095-OE) and dominant chimeric repressor-mediated suppression of ONAC095 (ONAC095-SRDX) were generated. ONAC095 protein had transactivation activity and the C2 domain in C-terminal was found to be critical for transactivation activity. ResultsĮxpression of ONAC095 was up-regulated by drought stress and abscisic acid (ABA) but down-regulated by cold stress. 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. 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.
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