Miscanthus NAC Transcription Factor MlNAC12 Positively Mediates Abiotic Stress Tolerance in Transgenic Arabidopsis

NAC (NAM, ATAF1/2 and CUC2) transcription factors play critical roles in plant abiotic stress responses. However, knowledge regarding the functional roles of NACs in abiotic stress tolerance and its underlying mechanisms is relatively limited in Miscanthus. In this study, we functionally characterized a novel Miscanthus NAC gene MlNAC12 by ectopic expression in Arabidopsis. MlNAC12 was localized in the nucleus. It could specifically binds to the NAC recognition sequence (NACRS) and has a transactivation activity in the C-terminus. Overexpression of MlNAC12 in Arabidopsis conferred hypersensitivity to exogenous Abscisic acid (ABA) at seed germination and root elongation stages. In addition, MlNAC12 overexpression enhanced germination and root growth under salt (NaCl) stress. Furthermore, MlNAC12 overexpression lines exhibited significantly enhanced drought stress tolerance, which was evidenced by a higher survival rate and a lower water loss rate compared to the wild type (WT). Accordingly, the stomata aperture was remarkably reduced in MlNAC12 overexpression lines in comparison to the WT under drought stress. Furthermore, the accumulation of the reactive oxygen species (ROS) and malondialdehyde (MDA) under abiotic stresses was significantly decreased, accompanied by dramatically enhanced activities of several antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in the transgenic plants. Correspondingly, the expression of six stress-responsive genes was significantly up-regulated in MlNAC12 overexpression lines. Together, our results indicate that MlNAC12 is a positive regulator of drought and salt stress tolerance through activating ROS scavenging enzymes.