The MADS-box transcription factor AaRLMA serves a crucial function in sustaining the integrity of cell wall, orchestrating secondary metabolites biosynthesis, and modulating pathogenicity in Alternaria alternata

RLMA, a transcription factor belonging to the MADS-box family, serves a pivotal function within the fungi cell wall integrity (CWI) pathway. This signaling cascade is responsible for sensing and responding to cellular wall stress signals, and is intimately linked to key aspects of fungal biology, including growth, development, and pathogenicity. Nevertheless, the precise regulatory functions of RLMA in Alternaria alternata have not been fully elucidated. In this study, we successfully cloned and performed functional characterization of AaRLMA. Remarkably, the knockout of AaRLMA led to a decrease in colony diameter, biomass production, and sporulation. Infection ability test revealed that ΔAaRLMA exhibited weakened cellophane penetration, along with reduced spore germination and appressorium-like formation. Additionally, ΔAaRLMA mutant exhibited heightened susceptibility to calcofluor white (CFW), concurrent with the downregulation of key genes involved in cell wall synthesis. Remarkably, an elevation in the content of secondary metabolite DHN (1,8-dihydroxynaphthalene) melanin was observed in the ΔAaRLMA, parallel to the downregulation of major melanin biosynthesis related genes. Furthermore, the pathogenicity of ΔAaRLMA was diminished under both wound-inoculated and non-wound-inoculated conditions, with significant decreases observed in the contents of several mycotoxins, and down-regulated of related genes expression. Additionally, enzymatic activity of cell wall degrading enzymes (CWDEs) were substantially lower in the ΔAaRLMA. This study offers fresh perspectives on the regulatory mechanisms underpinning the biological control of A. alternata.