ZmMPK5 ‐mediated ZmOCL1 phosphorylation positively regulates drought tolerance by promoting the induction of ZmDHN2 in maize

Transcription factors (TFs) play a critical role in regulating the expression of drought-responsive genes. Elucidating how TFs are modulated by stress signals will contribute to deciphering the impacts of drought on transcriptional regulation. We discovered that the mutation of an HD-Zip IV TF ZmOCL1 (OUTER CELL LAYER1) enhances susceptibility to water deficit. Transcriptome analysis and biochemical evidence demonstrated that a dehydrin gene ZmDHN2 is one of the direct target genes of ZmOCL1. Overexpression of ZmDHN2 in maize confers drought resistance by regulating stomatal closure, elevating peroxidase activity, and reducing hydrogen peroxide accumulation. Screening for an upstream kinase of ZmOCL1 identified a mitogen-activated protein kinase (MAPK) ZmMPK5, which is activated by dehydration. ZmMPK5 phosphorylates ZmOCL1 at the Ser283 residue and increases its binding affinity to the ZmDHN2 promoter, leading to full induction of ZmDHN2. Overexpression of ZmMPK5 improves drought tolerance and raises the transcription of ZmDHN2 compared to wild-type maize, while knockout of ZmMPK5 results in sensitivity to drought and a decrease in ZmDHN2 transcription. Our work reveals a transcriptional regulatory module in which ZmOCL1 promotes the expression of ZmDHN2 after being phosphorylated by ZmMPK5 in response to drought stress, finally resulting in better adaptation to water scarcity.