The cyclase-associated protein UvCap1 is required for mycelial growth and pathogenicity in the rice false smut fungus

Rice false smut caused by Ustilaginoidea virens is one of the widespread rice diseases across the globe in recent years, however, we know little about its molecular mechanism of infection. The cAMP signaling pathway functions directly in the development and formation of infectious structures to regulate the infection process in many pathogenic fungi. In order to investigate the role of the cAMP signaling pathway in U. virens, UvCap1, a cyclase-associated-protein homologous to Saccharomyces cerevisiae Srv2 was identified. Three targeted deletion mutants of the UvCAP1 gene were obtained with gene replacement strategy assisted with CRISPR-Cas9 system. The UvCAP1 deletion mutants showed defects in mycelial growth and conidial production. Inoculation experiments demonstrated that ΔUvcap1 exhibited defects in pathogenicity. Compared with the wild-type strain, ΔUvcap1 showed decreased tolerance to sorbitol and H2O2, and increased tolerance to NaCl, CFW and SDS, and the intracellular cAMP level was significantly reduced in ΔUvcap1. Yeast two-hybrid assay identified the interactions of UvCap1 with UvAc1 (adenylase cyclase), two Ras proteins (UvRas1 and UvRas2) and UvSte50. Taken together, as a component of cAMP signaling pathway, UvCap1 plays important roles in the development and pathogenicity of U. virens.