HvABI5 is an important ABA-dependent regulator of drought stress response at heading time in barley

Abscisic acid (ABA) and the ABA-dependent bZIP transcription factor ABA INSENSITIVE5 (HvABI5) are involved in regulating ecophysiological responses during the reproductive phase of barley under drought stress. Here, we show that a mutant allele of HvABI5, Hvabi5.d, exhibits disturbed photosynthesis and leaf stomatal closure in response to drought applied at heading (when the inflorescence emerges from the flag leaf), resulting in both reduced height and yield. Comparative transcriptome analysis of RNA from the second leaf below the flag leaf revealed increased expression of genes involved in stress response and jasmonic acid biosynthesis in Hvabi5.d under drought. In contrast, Flowering Locus T (HvFT) and auxin-related genes showed decreased expression. The metabolome of Hvabi5.d revealed increased amounts of dihydrojasmonic acid and the inactive auxin indole-3-carboxylic acid in response to drought. ABA treatment of Hvabi5.d at booting (when the flag leaf sheath extends and becomes visibly swollen) induced expression of ABA-dependent kinases along with barley MADS-box 3 (HvBM3) and barley MADS-box 8 (HvBM8), genes involved in flowering regulation, in leaves. Our data indicate that HvABI5 is a key ABA-dependent stress regulator in barley and plays an essential role in ABA crosstalk with jasmonic acid and auxin under drought at the reproductive phase of inflorescence development.