Globodera pallida RHA1B protein acts as a meta-effector, adding regulatory complexity to the effectorome by modulating other effector stability

Potato cyst nematode (Globodera pallida) is a major pest that threatens potato yield. Since genetic resistance is the most cost-effective and environmentally sustainable strategy for controlling plant-parasitic nematodes, understanding molecular plant-nematode interactions is essential for developing durable resistance. G. pallida deploys numerous effector proteins to manipulate host cell functions and suppress plant defenses. One such effector, RHA1B, functions as an E3 ubiquitin ligase, suppressing effector-triggered immunity by ubiquitinating plant proteins. Here, we hypothesize that RHA1B also acts as a meta-effector, regulating other nematode effectors. To test this, we examined RHA1B’s influence on five effectors (ME1-5) clustered within the same putative “effector island” as RHA1B. Using Agrobacterium-mediated transient expression in Nicotiana benthamiana, we co-expressed ME1-5 with RHA1B to assess ME protein stability via Western blotting and interactions via immunoprecipitation assays. Our data shows that RHA1B destabilized ME-1 and ME-4 in the E3-dependent manner, with direct interaction detected for ME-4. The roles of ME-1 and ME-4 in virulence were further tested through Hypersensitive Response suppression and ROS scavenging assays, both demonstrating that ME-4 interferes with host defenses. These findings suggest that, in addition to targeting host proteins, RHA1B also regulates the stability of other nematode effectors, adding a new layer of complexity to the nematode effectorome. This study identifies RHA1B as the first described meta-effector in nematodes.