Brachypodium histone deacetylase BdHD1 positively regulates ABA and drought stress responses

Despite recent evidence that HDACs are involved in the environmental stress responses of plants, their roles in the abiotic stress responses of monocot plants remain largely unexplored. We investigated a HDAC gene, Bradi3g08060 (BdHD1), in Brachypodium distachyon. The Brachypodium BdHD1-overexpression plants displayed a hypersensitive phenotype to ABA and exhibited better survival under drought conditions. On the other hand, the RNA-interference plants were insensitive to ABA and showed low survival under drought stress. At the genome-wide level, overexpression of BdHD1 led to lower H3K9 acetylation at the transcriptional start sites of 230 genes than in the wild type plants under the drought treatment. We validated our ChIP-Seq data on 10 selected transcription factor genes from the 230 drought-specific genes. These genes exhibited much lower expression in the BdHD1-overexpression plants compared to the wild type plants under drought stress. We further identified an ABA-inducible transcription factor gene BdWRKY24 that was repressed in BdHD1-OE plants, but highly expressed in RNA-interference plants under drought stress. These results indicate that BdHD1 plays a positive role in ABA sensitivity and drought stress tolerance and they provide a link between the role of BdHD1 and the drought stress response at a genome-wide level in Brachypodium.