A Conserved Glycoside Hydrolase Family 7 Cellobiohydrolase PsGH7a ofPhytophthora sojaeIs Required for Full Virulence on Soybean

Phytopathogens deploy glycoside hydrolases (GHs) to disintegrate plant cell walls for nutrition and invasion. However, the pathogenic mechanisms of the majority of GHs in virulence remain unknown, especially in oomycetes. In this study, aPhytophthora sojaegene encodes a GH7 family cellobiohydrolase, namedPsGH7a, was identified.PsGH7awas highly induced during the cyst germination and infection stages. PsGH7a is conserved in oomycetes, and shares a high amino acid sequence identity (>85%) withinPhytophthoragenus. The recombinant PsGH7a catalyzes the hydrolysis of beta-1,4-glucan and avicel, which represent the major components of cellulose in plant cell wall. The mutation of catalytic residue Glu236 to alanine resulted in a lower catalytic activity. In addition, the PsGH7a promotesPhytophthorainvasion, while the mutant can not. Notably, PsGH7a protein triggers hypersensitive cell death in diverse plants. PsGH7a knockout mutants were generated via CRISPR/Cas9 system, to investigate its biological function. Compared to wild-type strain P6497, the mutants showed reduced virulence on susceptible soybean, indicates PsGH7a is indispensable toP. sojaevirulence.