Glycogen synthase kinase 3 (GSK3)–like kinases play important roles in stress responses in plants. However, the mechanism of GSK3-like kinases in drought-induced antioxidant defense is not clear. In this study, we discovered that the GSK3-like kinase SHAGGY-like kinase 1 (ZmSK1) negatively regulates drought tolerance by inhibiting antioxidant defense in maize (Zea mays). Then, we determined that cysteine-rich polycomb-like protein 2 (ZmCPP2) interacts with ZmSK1 and enhances maize drought tolerance by inducing antioxidant defense. ZmCPP2 is phosphorylated at Ser-250 by ZmSK1, which is dependent on ZmSK1 kinase activity and attenuates maize drought tolerance. Furthermore, ZmCPP2 directly binds to the promoter of the superoxide dismutase (SOD) gene ZmSOD4, encoding an antioxidant defense enzyme, and activates its expression. ZmSK1 phosphorylating ZmCPP2 at Ser-250 represses the binding of ZmCPP2 to the ZmSOD4 promoter. Taken together, our results indicate that the phosphorylation of ZmCPP2 by ZmSK1 results in decreased SOD activity and thus reduces drought tolerance in maize. These findings reveal a mechanism of GSK3-like kinases regulating antioxidant defense in the drought stress response.

Salt stress significantly impairs plant growth, presenting a challenge to agricultural productivity. Exploring the regulatory mechanisms underlying salt stress responses is critically important. Here, we identified a significant role for the maize LESION-SIMULATING DISEASE transcription factor, ZmLSD1, in enhancing salt stress response. Subcellular localization analysis indicated that ZmLSD1-GFP was localized in the nucleus in the maize protoplast. Overexpressing ZmLSD1 in maize obviously enhanced the tolerance of plants to salt stress. Physiological analysis indicated that overexpressed ZmLSD1 in maize could mitigate the accumulation of H₂O₂ and MDA content exposed to salt stress. RNA-seq and qPCR-PCR analyses showed that ZmLSD1 positively regulated ZmWRKY29 expression. ChIP-qPCR and EMSA experiments demonstrated that ZmLSD1 could directly bind to the promoter of ZmWRKY29 through the GTAC motif both in vitro and in vivo. Overall, our findings suggest that ZmLSD1 plays a positive role in enhancing the tolerance of maize to salt by affecting ZmWRKY29 expression.