PpZAT12 from a native Kentucky bluegrass (Poa pratensis L.) confers drought tolerance through regulating antioxidant defense system and multiple metabolic pathways

Kentucky bluegrass is a worldwide planted turfgrass species, but it is sensitive to drought. The molecular response and function of the genes associated with drought tolerance remain largely unknown. The objectives of this study were to isolate the drought responsive PpZAT12 and examine its role in regulation on drought tolerance in the present study. PpZAT12 localized in the nucleus and had transcriptional activation activity. Its expression was rapidly induced within 48 h under osmotic stress. Overexpression of PpZAT12 in transgenic rice resulted in enhanced drought tolerance, with higher relative water content and lower ion leakage compared with the wild type (WT) after osmotic stress. Superoxide dismutase, catalase, and ascorbate peroxidase activities and proline concentration were increased after osmotic stress with higher levels in PpZAT12-overexpressing lines compared with WT. Transcriptomic analysis revealed that overexpression of PpZAT12 altered expression of hundreds of genes under osmotic stress. Specifically, the genes involving starch, sugars, and amino acids biosynthesis and metabolism were altered. For example, granule-bound starch synthase Ⅱ (GBSSⅡ), glycogen phosphorylase 1 (Pho1), β-amylase 1 (BAM1), and β-glucosidases 1/24/28 (BGL1/24/28), trehalose-6-phosphate synthase 8 (TPS8), and mannan synthase 1/2 (MAN1/2) were upregulated, which led to higher concentrations of glucose, fructose, trehalose, and mannose in PpZAT12-overexpressing lines than in WT under osmotic stress, which was associated with the enhanced drought tolerance. In addition, the genes involving glycolysis were upregulated in the PpZAT12-overexpressing line, indicating that PpZAT12 regulates glycolysis under osmotic stress. Moreover, the genes involving glycine, serine and threonine metabolism, lysine biosynthesis, and biosynthesis of amino acids were altered. RT-qPCR analysis showed that OsSAMS2 and OsABAT transcripts were higher and lower, respectively, in the PpZAT12-overexpressing line under osmotic stress compared with WT, which allow plants to accumulate more polyamines and GABA to enhance drought tolerance. The drought induced PpZAT12 expression confers drought tolerance through activating antioxidant defense system and regulating gene expression involving starch, sugars and amino acids biosynthesis and metabolism.