Autophagy contributes to resistance to the oxidative stress induced by pine reactive oxygen species metabolism, promoting infection by Bursaphelenchus xylophilus.

Abstract

Autophagy plays an important role in eukaryotes. We investigated its role in the pine wood nematode (PWN), Bursaphelenchus xylophilus, the causative agent of pine wilt disease (PWD), to find promising control strategies against PWD. We analysed the expression levels of PtRBOH1 and PtRBOH2, which regulate reactive oxygen species (ROS) metabolism, in Pinus thunbergii and the expression of three autophagy genes, BxATG5, BxATG9 and BxATG16, in PWN by quantitative reverse transcription-polymerase chain reaction (qRT-PCR), and measured the content of H2 O2 , the main product of ROS metabolism, in pine stem. There was a correlation between the expression of autophagy genes in PWN and pine ROS metabolism during early infection. We also found that oxidative stress induces autophagy in PWN according to qRT-PCR, transmission electron microscopy and Western blot analyses. Inhibition of autophagy by 3-methyladenine or silencing of the autophagy genes BxATG9 and BxATG16 in PWN showed that autophagy is essential for feeding, fecundity, egg hatching and survival of PWN under oxidative stress, confirming the importance of autophagy in the antioxidant defences of PWN. Similarly, we demonstrated that autophagy contributes to the virulence of PWN. Moreover, PWN likely ameliorates oxidative damage by enhancing the activities of the peroxidase and catalase antioxidant pathways when autophagy is inhibited. Autophagy contributes to resistance to the oxidative stress induced by pine ROS metabolism, thus promoting infection by PWN. Our findings clarify the defence mechanisms of PWN and the pathogenesis of PWD, and provide promising hints for control of PWD by blocking autophagy. © 2020 Society of Chemical Industry.