Pathogen effector forms a hexameric phosphatase holoenzyme with host core enzyme to promote disease

Pathogen effectors play critical roles in pathogenesis by directly manipulating host cellular processes. The Ser/Thr protein phosphatase 2A (PP2A) is commonly targeted by pathogens. Effectors from devastating plant pathogen Phytophthora hijack the PP2A core enzyme in plant hosts, altering the host phosphoproteome. In this study, we present a series of cryo-electron microscopy structures of the Phytophthora effector PSR2 in complex with the host PP2A core enzyme to form a functional holoenzyme. The PSR2-PP2A complex adopts a unique hexameric architecture, driven by PSR2-mediated dimerization of two heterotrimers. This hexamer exhibits greater stability and features a more exposed catalytic pocket compared to the canonical trimeric form of PP2A, likely enhancing its virulence activity. Mutational analyses underscore the importance of this hexameric structure for PSR2s virulence function. These findings provide mechanistic insights into pathogen-mediated manipulation of a key host phosphatase and offer targets for developing disease resistance strategies.