The Verticillium dahliae effector VdPHB1 promotes pathogenicity in cotton and interacts with the immune protein GhMC4.

Verticillium dahliae is a kind of pathogenic fungus that brings about wilt disease and great losses in cotton. The molecular mechanism of the effectors in V. dahliae regulating cotton immunity remains largely unknown. Here we identified an effector of V. dahliae, VdPHB1, whose gene expression is highly induced by infection. VdPHB1 protein is localized in the intercellular space of cotton plants. Knockout VdPHB1 gene in V. dahliae had no effect on pathogen growth, but decreased the virulence in cotton. VdPHB1 ectopically expressed Arabidopsis plants were growth-inhibited and significantly susceptible to V. dahliae. Further, VdPHB1 interacted with the type II metacaspase GhMC4. GhMC4 gene silenced cotton plants were more sensitive to V. dahliae with reduced expressions of pathogen defense-related and programmed cell death genes. The accumulation of GhMC4 protein were concurrently repressed when VdPHB1 protein expressed during infection. In summary, these results revealed a novel molecular mechanism of virulence regulation that the secreted effector VdPHB1 represses the activity of cysteine protease for helping V. dahliae infection in cotton.