A pioneer nematode effector suppresses plant reactive oxygen species burst by interacting with the class III...

Bursaphelenchus xylophilus is the pathogen of pine wilt disease, which can devastate the pine forest ecosystem. Usually, plant cells generate reactive oxygen species (ROS) as a defensive substance or signalling molecules to resist the infection of nematodes. However, little is known about how B. xylophilus effectors mediate the plant ROS metabolism. Here, we identified a pioneer B. xylophilus Prx3-interacting effector 1 (BxPIE1) expressed in the dorsal gland cells and the intestine. Silencing of the BxPIE1 gene resulted in reduced nematode reproduction and a delay in disease progression during parasitic stages, with the upregulation of pathogenesis-related (PR) genes PtPR-3 (class Ⅳ chitinase) and PtPR-9 (peroxidase). The protein-protein interaction assays further demonstrated that BxPIE1 interacts with a Pinus thunbergii class III peroxidase (PtPrx3), which produces H₂O₂ under biotic stress. The expression of BxPIE1 and PtPrx3 was upregulated during the infection stage. Furthermore, BxPIE1 effectively inhibited H₂O₂ generating from class III peroxidase and ascorbate can recover the virulence of siBxPIE1-treated B. xylophilus by scavenging H₂O₂. Taken together, BxPIE1 is an important virulence factor, revealing a novel mechanism utilized by nematodes to suppress plant immunity.