Abstract
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, a Phytophthora sojae gene encodes a GH7 family cellobiohydrolase, named PsGH7a, was identified. PsGH7a was highly induced during the cyst germination and infection stages. PsGH7a is conserved in oomycetes, and shares a high amino acid sequence identity (>85%) within Phytophthora genus. The recombinant PsGH7a catalyzes the hydrolysis of β-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 promotes Phytophthora invasion, 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 to P. sojae virulence.
Highlights
The battle between plants and microbes is the product of million-years of co-evolution
Many plant-pathogenic fungi secrete a range of cell wall degrading enzymes (CWDEs) to degrade the host cell wall, such as glycoside hydrolases, polysaccharide lyases, and esterases, PsGH7a Contribute to P. sojae Virulence even much more than that in Trichoderma reesei, which is known as a major industrial cellulase-producing fungus
P. sojae strain P6497 and Phytophthora capsici strain LT1534 and all transformants were grown on 10% V8 medium at 25◦C in the dark. 1 × 1-mm hyphal plugs were cultured in V8 liquid medium
Summary
The battle between plants and microbes is the product of million-years of co-evolution. Phytopathogenic fungi and oomycetes are unique microbial pathogens that being able to break the intact physical surfaces of host plants (Soanes et al, 2007). Many plant-pathogenic fungi secrete a range of CWDEs to degrade the host cell wall, such as glycoside hydrolases, polysaccharide lyases, and esterases, PsGH7a Contribute to P. sojae Virulence even much more than that in Trichoderma reesei, which is known as a major industrial cellulase-producing fungus From the kingdom Stramenopila (Baldauf, 2003; Yutin et al, 2008), encompass numerous phytopathogens such as Phytophthora, Pythium, Albugo, and downy mildews, which genomes encode abundant of CWDEs toward plant cell wall components (Tyler et al, 2006; Haas et al, 2009; Baxter et al, 2010). The pathogenetic roles of the vast majority of CWDEs remain unknown, especially in oomycetes (Ma Z. et al, 2015)
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