Over-expression of the Brachypodium ASR gene, BdASR4, enhances drought tolerance in Brachypodium distachyon.

KEY MESSAGE: BdASR4 expression was up-regulated during abiotic stress and hormone treatments. Plants over-expressing BdASR4 improved drought tolerant. BdASR4 may regulate antioxidant activities and transcript levels of stress-related and abscisic acid-responsive genes. Abiotic stress conditions negatively affect plant growth and developmental processes, causing a reduction in crop productivity. The abscisic acid-, stress-, ripening-induced (ASR) proteins play important roles in the protection of plants from abiotic stress. Brachypodium distachyon L. is a well-studied monocot model plant. However, ASR proteins of Brachypodium have not been widely studied. In this study, five ASR genes of Brachypodium plant were cloned and characterized. The BdASR genes were expressed in response to various abiotic stresses and hormones. In particular, BdASR4 was shown to encode a protein containing a nuclear localization signal in its C-terminal region, which enabled protein localization in the nucleus. To further examine functions of BdASR4, transgenic Brachypodium plants harboring BdASR4 were generated. Over-expression of BdASR4 was associated with strong drought tolerance, and plants over-expressing BdASR4 preserved more water and displayed higher antioxidant enzyme activities than did the wild-type plants. The transcript levels of stress-responsive genes, reactive oxygen species scavenger-associated genes, and abscisic acid-responsive genes tended to be higher in transgenic plants than in WT plants. Moreover, plants over-expressing BdASR4 were hypersensitive to exogenous abscisic acid at the germination stage. Taken together, these findings suggest multiple roles for BdASR4 in the plant response to drought stress by regulating antioxidant enzymes and the transcription of stress- and abscisic acid-responsive genes.