Phytophthora sojae effector Avr1d functions as an E2 competitor and inhibits ubiquitination activity of GmPUB13 to facilitate infection

Significance Ubiquitination acts as a crucial regulator in plant immunity. Accordingly, microbial pathogens secrete effectors to hijack the host ubiquitination system. However, the molecular mechanisms by which effectors modulate the host ubiquitination system are not yet clear. Here, we found that thePhytophthora sojae effector Avr1d physically binds to the U-box-type E3 ligase GmPUB13, which proved to be a susceptibility factor. The crystal structure of Avr1d complexed with GmPUB13 revealed that Avr1d occupies the binding site in GmPUB13 for E2 ubiquitin conjugating enzyme and competes with E2 for binding to GmPUB13. Avr1d stabilized GmPUB13 by suppressing the self-ubiquitination activity of GmPUB13 and thereby promotingPhytophthora infection. This study reveals a structural basis for modulation of host targets byPhytophthora effectors.