Host-dependent contributions of the Cfcdp1 protease gene to virulence in the entomopathogenic fungus Cordyceps fumosorosea

BACKGROUND The genomes of broad host range insect pathogenic fungi, including Cordyceps fumosorosea, encode for a suite of secreted proteases implicated in targeting, penetration, and degradation of the host exoskeleton or cuticle. These cuticle-degrading proteases act as critical virulence factors, but their functions within the biological context, particularly in relation to host specificity, remain poorly characterized. RESULT A C. fumosorosea protease gene, Cfcdp1, was identified and a targeted gene-knockout strain constructed. Minor growth defects were observed for the Delta Cfcdp1 strain when compared to the wild-type parent and complemented (Delta Cfcdp1::Cfcdp1) strains, with delayed and decreased sporulation noted for the mutant. Decreased subtilisin-like protease activity was seen for the Delta Cfcdp1 strain, although total secreted protease activity was similar between the mutant and wild-type strains. Insect bioassays using whitefly, Bemisia tabaci, and cabbageworm, Pieris rapae, showed decreased infectivity, i.e. 2.4-3.4-fold increase in lethal dose (LC50) and an increased time to death (LT50), for the Delta Cfcdp1 strain. In contrast, insect bioassays using the diamondback moth, Plutella xylostella, or the brown planthopper, Nilaparvata lugens, showed increased infectivity, i.e. a 3-5-fold decrease in LC50, and a decreased LT50. Differential effects were also seen on the fecundity of B. tabaci infected by the different fungal strains. CONCLUSION These data reveal host-dependent effects of a protease implicated in cuticle degradation on C. fumosorosea virulence. The implications of these findings in suggesting context-dependent requirements of cuticle-degrading enzymes and their potentially differential roles in mediating virulence towards different hosts are discussed. (c) 2019 Society of Chemical Industry