Transcriptome and molecular evidence of HvMORF8 conferring drought-tolerance in barley

Drought is one of the most devastating abiotic stresses worldwide, which severely limits crop yield. Tibetan wild barley is a treasure trove of useful genes for crop improvement including drought tolerance. Here, we detected large-scale changes of gene expression in response to drought stress with a substantial difference among contrasting Tibetan barley genotypes XZ5 (drought-tolerant), XZ54 (drought-sensitive) and cv. Tadmor (drought-tolerant). Drought stress led to upregulations of 142 genes involved in transcription, metabolism, protein synthesis, stress defense, transport and signal transduction in XZ5, but those genes were down-regulated or unchanged in XZ54 and Tadmor. We identified and functionally characterized a novel multiple organellar RNA editing factors 8 (HvMORF8), which was up-regulated by drought stress in XZ5, but unchanged in XZ54 and Tadmor under drought stress. Phylogenetic analysis showed that orthologues of HvMORF8 can be traced back to the closest gymnosperm species such as Cycas micholitzii, implicating a potential evolutionary origin for MORF8 from a common ancestor in early seed plants. Virus-induced HvMORF8 silencing in XZ5 led to hypersensitivity to drought stress, demonstrating it is a positive regulator of drought tolerance in barley. RNA sequencing of BSMV:HvMORF8 and control plants reveals that silencing of HvMORF8 suppresses genes involved in osmolytes transport, cell wall modification and antioxidants, resulting in water metabolism disorder and overaccumulation of reactive oxygen species (ROS) under drought stress. Therefore, we propose HvMORF8-mediated regulatory drought tolerance mechanisms at transcriptomic level in XZ5, providing new insight into the genetic basis of plastid RNA editing function of HvMORF8 for barley drought tolerance.