Research Article

A paralogous decoy protects Phytophthora sojae apoplastic effector PsXEG1 from a host inhibitor

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Science  17 Feb 2017:
Vol. 355, Issue 6326, pp. 710-714
DOI: 10.1126/science.aai7919

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Host-pathogen point-counterpoint

The arms race between pathogen and host is a well-known phenomenon. Ma et al. have now identified how an enzymatically inactive protein can abet a pathogen's infectivity. The pathogenic oomycete Phytophthora sojae secretes xyloglucanase that damages soybean cell walls. Soybean, in turn, secretes a defense protein that binds to and inactivates the xyloglucanase. To counteract this plant defense, the oomycete deploys a product of its own gene duplication: an inactive enzyme that binds the plant's defense protein. With the defense protein unproductively bound to the decoy, the oomycete can successfully invade the soybean cells.

Science, this issue p. 710


The extracellular space (apoplast) of plant tissue represents a critical battleground between plants and attacking microbes. Here we show that a pathogen-secreted apoplastic xyloglucan-specific endoglucanase, PsXEG1, is a focus of this struggle in the Phytophthora sojae–soybean interaction. We show that soybean produces an apoplastic glucanase inhibitor protein, GmGIP1, that binds to PsXEG1 to block its contribution to virulence. P. sojae, however, secretes a paralogous PsXEG1-like protein, PsXLP1, that has lost enzyme activity but binds to GmGIP1 more tightly than does PsXEG1, thus freeing PsXEG1 to support P. sojae infection. The gene pair encoding PsXEG1 and PsXLP1 is conserved in many Phytophthora species, and the P. parasitica orthologs PpXEG1 and PpXLP1 have similar functions. Thus, this apoplastic decoy strategy may be widely used in Phytophthora pathosystems.

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