PpbZIP23 from a native Kentucky bluegrass (Poa pratensis L.) regulates osmotic stress tolerance in transgenic rice

A drought-induced bZIP transcription factor from a native Kentucky bluegrass (Poa pratensis L.), PpbZIP23, in regulating drought tolerance was investigated in the present study. PpbZIP23 is located in the nucleus and has transcriptional activation activity. PpbZIP23 expression was induced within 48 h after treatment with osmotic stress. Overexpression of PpbZIP23 led to delayed wilting and enhanced drought tolerance with higher levels of relative water content and lower levels of ion leakage after osmotic stress. Superoxide dismutase, catalase, and ascorbate-peroxidase activities and proline concentrations of proline increased after osmotic stress, with higher levels in the PpbZIP23-overexpressing lines than in the wild type plants. Transcriptomic analysis showed that overexpression of PpbZIP23 led to upregulation and downregulation of hundreds of genes under osmotic stress conditions. The differentially expressed genes were enriched in multiple KEGG pathways. PpbZIP23 regulated glycerophospholipid and ascorbic acid metabolism through upregulating Glycerol-3-Phosphate Acyltransferase 3, Choline Kinase Alpha 2, UDP-Glucose Dehydrogenase, and Ascorbate-Peroxidase 3 expressions. PpbZIP23 regulated zeatin metabolism through downregulating Isopentenyl Transferase 8, Cytokinin Oxidase/dehydrogenase 1 expressions and promoted triterpenes and phytosterols biosynthesis via upregulating Oxidosqualene Cyclase 7 expression. Lignin biosynthesis was also regulated by PpbZIP23 through upregulating Cinnamoyl-CoA Reductase 17 (CCR17), class III Peroxidases (PRX16) and PRX72 and downregulating p-Hydroxycinnamoyl Transferase 1, CCR13, PRX1, PRX62, and PRX95 expressions. The results suggest that PpbZIP23 regulates drought tolerance through activating antioxidant defense system and altering multiple metabolic pathways.