Wheat WRKY Type Transcription Factor Gene TaWRKY1 is Essential in Mediating Drought Tolerance Associated with an ABA-Dependent Pathway

WRKY-type transcription factors (TFs) are important regulators in plant growth, development and responses to diverse biotic and abiotic stresses. In this study, we characterized the function of TaWRKY1, a wheat (Triticum aestivum) WRKY family gene, in mediating plant tolerance to drought. TaWRKY1 bears a conserved WRKY motif and a C2H2 domain and targets onto the nucleus under both normal and simulated drought conditions. On exposure to simulated drought and ABA, the TaWRKY1 expression levels were significantly up-regulated. Ectopic overexpression of TaWRKY1 in tobacco conferred improved tolerance to drought; the transgenic plants exhibited more biomass, slower leaf water loss rate (WLR), more osmolyte accumulation, and higher antioxidant enzyme activities than wild type (WT) plants after drought treatments. In addition, the stomata closure rate was promoted in the transgenic plants upon exposure to drought and -exogenous ABA with respect to that in WT plants, suggesting that TaWRKY1 mediates the stomata movement and impacts the leaf water retention capacity. The transcripts of NtPYL8, an ABA receptor gene in tobacco, were shown to be induced in the TaWRKY1-overexpressing plants under drought and ABA stresses. Moreover, overexpression and knockdown of NtPYL8 modified the stomata movement characterization, leaf WLR, and phenotype of the seedlings upon exposure to the drought stress. These findings suggest that NtPYL8 acts as one of the critical players in transducing ABA signaling initiated by osmotic stress, contributing to the TaWRKY1-mediated drought tolerance via regulating stomata movement and plant water retention capacity. Our findings together reveal that TaWRKY1 plays an important role in mediating the plant tolerance to drought through modification of a set of osmotic stress-defensive processes connecting an ABA-dependent pathway. NtPYL8 and its homolog in wheat are crucial members in transducing the drought-initiated ABA signaling and are functional in modulating stomata movement.