Mutation of ZmWRKY87 increases maize salt sensitivity by regulating ZmPP2C4 expression

Salt stress severely constrains the sustainable development of global agricultural production. Maize (Zea mays L.), as a crucial food and feed crop, holds significant importance in elucidating its salt tolerance molecular mechanisms to ensure food security. In this study, we identified a group IIb WRKY gene, ZmWRKY87, whose expression is induced by salt and is relatively high in tissues such as roots at the three-leaf stage, stems, and tassels at the silking stage. ZmWRKY87 is localized in the nucleus and does not exhibit transcriptional autoactivation activity in yeast. ZmWRKY87 may function as a positive regulator of salt tolerance, evidenced by the compromised salinity resilience in zmwrky87 mutants and the enhanced salt stress tolerance conferred by its heterologous expression in yeast. Integrated transcriptome and promoter analysis identified ZmPP2C4 as a key downstream target gene that is significantly upregulated in the zmwrky87 mutants compared to B73 plants under salt stress. Electrophoretic mobility shift assay and dual-luciferase reporter assays demonstrated that ZmWRKY87 specifically binds to the W-box element in the promoter region of ZmPP2C4 and represses its transcription. This finding is consistent with the expected expression levels of ZmPP2C4 observed in the mutant. In conclusion, these findings enhance our understanding of WRKY functions and provide potential targets for crop improvement.