Alternaria alternata Effector Aa593 Promotes Virulence by Hijacking the CmNAC29-Mediated Abscisic Acid Biosynthesis...

The interaction between plants and pathogens has long been an actively researched field of plant immunity. In this study, we found an Aa593/CmNAC29-CmNCED3 module associated with the interaction between chrysanthemum and the fungal pathogen Alternaria alternata. Here, we identified a transcription factor, CmNAC29, in chrysanthemum that promotes abscisic acid (ABA) biosynthesis by directly regulating CmNCED3, a key rate-limiting enzyme gene for ABA synthesis, thereby determining the susceptibility of plants to A. alternata. On invading plants, pathogens secrete effectors that contribute to regulating plant immune responses. Interestingly, we screened a novel effector, Aa593, secreted by A. alternata that targets CmNAC29 in the plant cell nucleus. By interacting with CmNAC29 and thus enhancing its transcriptional activation activity, Aa593 promotes ABA biosynthesis and subsequently weakens plant resistance to A. alternata. Furthermore, genetic transformation assays indicated Aa593 contributes to the virulence of A. alternata. Our findings in this study have enabled us to elucidate how fungal effectors target plant hormone signalling pathways to promote their virulence and lay the theoretical foundations for further studies on the pathogenic mechanism of necrotrophic fungi.