Yeast secreted protein PgSCP interacts with citrus transcription factors CsFAR1 to enhance green mold resistance in fruit

Green mold caused by Penicillium digitatum significantly impacts the citrus industry economically. Enhancing postharvest disease resistance in citrus fruit remains challenging due to the complex pathogen-citrus interaction. Previous researches have indicated that PgSCP, a small cysteine-rich secreted protein derived from Pichia galeiformis, activates resistance responses in citrus fruit. However, the precise molecular mechanisms underlying this effect remain unclear. This study showed that PgSCP enhances disease resistance gene expression and substance accumulation in citrus fruit. Additionally, potential citrus proteins that may interact with PgSCP was identified. Among these, four candidate transcription factors were identified: CsFAR1, CsMIKC, CsLBD, and CsGRAS. Subsequent validation demonstrated that PgSCP interacts with the citrus transcription factor CsFAR1. Transient overexpression analysis demonstrated that CsFAR1 positively regulates resistance to green mold, and CsFAR1 also enhances the disease resistance gene expression in citrus fruit. The CsFAR1 protein enhances resistance by activating DHAPS-1, GSH1, ACO1, INVA, PAL6, OMT, CYP73A16, CCOAOMT1, CYP73A4, PER16, and COMT1. These findings suggest that the yeast-secreted protein PgSCP may act as an elicitor that interacts with citrus transcription factors CsFAR1 to enhance host defense responses, thereby contributing to improved postharvest resistance to green mold.