Transcription Factor PFB1 Is Required for the Botrytis cinerea Effector BcSCR1-Mediated Pathogenesis

Botrytis cinerea is a necrotrophic fungus that infects more than 200 plant species, causing significant economic losses worldwide. Due to its diverse pathogenicity, extensive efforts have been made to unravel its pathogenic mechanisms. However, the function of the effectors underlying B. cinerea virulence remains largely unknown. In this study, we identified an effector BcSCR1 (B. cinerea small cysteine-rich protein 1) and found that it interacts with the transcription factor PFB1 (Pericycle Factor Type-B1) in Arabidopsis thaliana. Ectopic expression of BcSCR1 in plants resulted in decreased resistance to B. cinerea infection, while disruption of BcSCR1 in B. cinerea significantly decreased its aggressiveness toward host plants. In addition, the mutation of PFB1 in Arabidopsis increased resistance of plants to B. cinerea infection. PFB1 directly activated the expression of OPR3 and WRKY33 under normal conditions, while the binding of BcSCR1 to PFB1 repressed its transcriptional activation activity during B. cinerea infection. These findings reveal that B. cinerea employs the effector protein BcSCR1 to promote infection by suppressing the plant's immune defences.