The Phytophthora sojae Effector PsAvh208 Hijacks Host Aquaporin Tetramerization to Establish a Water Soaked Infection Niche

A fundamental strategy for microbial pathogens is the manipulation of the host environment to create conditions favorable for colonization. A hallmark of such manipulation in plant diseases is the “water-soaked” lesion, an aqueous apoplastic niche. While bacterial effectors that induce water soaking are known, the mechanisms employed by eukaryotic microbial pathogens, such as oomycetes, remain entirely elusive. Here, we uncover a novel virulence strategy whereby a pathogen effector directly targets the quaternary structure of a plant aquaporin to dysregulate water homeostasis. We demonstrate that the apoplastic effector PsAvh208 of Phytophthora sojae interacts with the soybean aquaporin GmPIP2;6, a plasma membrane intrinsic protein that facilitates water transport. This interaction specifically disrupts the homomeric assembly of GmPIP2;6 into functional tetramers, thereby impairing water conductance and leading to apoplastic water accumulation. Crucially, PsAvh208-mediated suppression of tetramerization does not interfere with the intrinsic immune-suppressive function of GmPIP2;6 monomers. The resulting water-soaked niche promotes infection by both P. sojae and the co-infiltrated bacterial pathogen Pseudomonas syringae, indicating its broad permissiveness. Our findings reveal the manipulation of aquaporin oligomerization as a previously unknown virulence mechanism, positioning water homeostasis as a critical battleground in plant-microbe interactions. This work provides a conceptual advance in understanding how pathogens rewire host physiology to establish a favorable microenvironment for disease.