Molecular mechanism of ZmWRKY36 mediated maize resistance to Bipolaris maydis

WRKY transcription factors (TFs) represent one of the largest families of transcriptional regulators in plants, playing a crucial role in plant responses to both biotic and abiotic stresses. Studies have shown that WRKY family members modulate the expression of disease resistance genes, hormone synthesis genes and signal transduction genes, thereby mediating plant resistance to diverse pathogens including fungi, bacteria, and viruses. Although reports have indicated the presence of 120 WRKY family proteins in maize (Zea mays L), research on the molecular regulatory mechanism underlying disease resistance mediated by maize WRKY genes remains limited. In this study, we identified the transcription factor gene ZmWRKY36 in maize and investigated its function in maize's response to infection by Bipolaris maydis, the causal agent of southern corn leaf blight. This work aims to provide a theoretical and experimental basis for exploring maize disease resistant genes and enriching functional studies of WRKY TFs in different crops.

We identified ZmWRKY36 as a nuclear-localized transcription factor in maize. To explore its biological function in resistance to B. maydis, we constructed ZmWRKY36-silenced (FoMV:ZmWRKY36-VIGS) and ZmWRKY36-overexpressed (FoMV:ZmWRKY36-VOX) maize plants using virus-induced gene silencing (VIGS) and transient overexpression (VOX) systems, respectively. Disease resistance assays revealed that transiently silenced FoMV:ZmWRKY36-VIGS plants exhibited reduced resistance to B. maydis infection and suppressed chitin-induced reactive oxygen species (ROS) burst, whereas transiently overexpressed FoMV:ZmWRKY36-VOX plants showed the opposite results. Additionally, overexpressed of ZmWRKY36 upregulated the expression of disease-related genes, suggesting that ZmWRKY36 positively regulates maize resistance to B. maydis. Further functional characterization demonstrated that ZmWRKY36 possesses transcriptional activation activity. Transcriptome analysis of ZmWRKY36-silenced and ZmWRKY36-overexpressed plants revealed that the differentially expressed genes (DEGs) were mainly enriched in pathways related to cellular structure composition, metabolic synthesis, and photosynthesis. Promoter analysis of these DEGs identified 105 genes containing W-box elements the core binding motif of WRKY TFs, which suggested that these pathways and target genes are involved in mediating maize resistance to B. maydis.

These results demonstrate that transcription factor ZmWRKY36 positively regulates maize resistance to B. maydis and identify its potential downstream target genes. This study provides insights into the regulatory role of ZmWRKY36 in maize defense responses and lays a foundation for further dissecting WRKY-mediated disease resistance networks in maize.