Arabidopsis O-GlcNAc transferase AtSEC modifies the transcription factor AtWRKY1 to negatively regulate resistance to Pseudomonas syringae

In Arabidopsis, O-GlcNAc transferase (OGT) AtSEC catalyze the formation of glycosidic bonds by linking the sugar donor UDP-GlcNAc to Ser/Thr residues of target proteins. AtSEC has been demonstrated to regulate various biological processes, including embryonic development flowering time and hormone signaling pathways. However, its role in biotic stress responses remains largely unexplored. In this study, we found that AtSEC negatively regulates Arabidopsis resistance to P.syringae. Overexpression of AtSEC impaired the resistance of Arabidopsis to P. syringae, while sec mutants exhibited enhanced resistance, as demonstrated by bacterial quantification, phenotypic observations, and the expression analysis of pathogenesis-related genes. Subsequently, downstream targets of AtSEC were identified through glycoproteomic profiling conducted on sec mutants. Gene Ontology (GO) enrichment analysis revealed that AtWRKY1, a transcription factor enriched in the salicylic acid-mediated signaling pathway, is a potential target protein. The physical interaction between AtSEC and AtWRKY1 was further confirmed, and AtWRKY1 was found to be O-GlcNAcylated by AtSEC at threonine 41. Protein degradation assays further indicated that AtSEC promotes the degradation of AtWRKY1. Transcriptomic profiling following Psm ES4326 infection revealed that multiple defense-associated genes, particularly PR1, were upregulated in the wrky1 mutant, while being suppressed in 35S:AtWRKY1 lines. Furthermore, Yeast one-hybrid and ChIP assays demonstrated that AtWRKY1 physically associates with the PR1 promoter, thereby repressing its transcriptional activation. Taken together, these findings reveal the crucial roles of AtSEC and AtWRKY1 in plant immunity.