Science doi:10.1126/science.aai7919 (2017)

Credit: AAAS

Pathogen infection of plants results in the recognition of pathogen-associated molecular patterns (PAMPs) by the host, leading to a defense response. The soybean pathogen Phytophthora sojae, which causes soybean root and stem rot, releases a glycoside hydrolase protein, PsXEG1, during infection that is recognized as a PAMP by the host. To further understand how soybeans might counteract PsXEG1, Ma et al. used a proteomic approach in P. sojae–infected soybeans and identified a xyloglucan-specific glucanase inhibitor protein (GmGIP1) as a direct binder of PsXEG1. GmGIP1 blocked PsXEG1-mediated enzymatic activity and infection. GmGIP1 also interacted with the related XEG-like protein 1 (PsXLP1), which promoted pathogen virulence. Interestingly, transgenic P. sojae lines expressing a PsXLP1 catalytic mutant resembled wild-type P. sojae, while lines deficient in GmGIP1 binding showed reduced virulence, suggesting that the interaction of PsXLP1 with GmGIP1 was essential for pathogen infection. ITC binding studies demonstrated that the interaction between GmGIP1 and PsXLP1 was five times stronger than the GmGIP1–PsXEG1 interaction. The authors proposed that the coexpression of PsXLP1 with PsXEG1 during infection results in PsXLP1 binding to GmGIP1, freeing PsXEG1 to promote infection. Given that homologs of PsXLP1 and PsXEG1 are found in other Phytophthora species, it is possible that this decoy mechanism may be a conserved strategy of counter-defense by pathogens against plants.