Functional characterization of parasitism-related genes from Bursaphelenchus xylophilus may suggest involvement on the nematode oxidative stress response

Abstract

The pinewood nematode Bursaphelenchus xylophilus is a migratory plant-parasitic nematode that infects conifer pine trees (mainly Pinus species) causing the pine wilt disease. In Portugal, the maritime pine, Pinus pinaster, is the most susceptible conifer species, and its decline has ecological and economic impact on forest ecosystems and wood industry1. Functional studies suggest that effectors are one key part of a multi-layered detoxification strategy deployed by B. xylophilus in order to protect itself from host defense responses. B. xylophilus secretes detoxification enzymes into the host, while simultaneously upregulating other detoxification enzymes within its digestive system2. Previous transcriptomic data from pre-parasitic and parasitic stages revealed differentially expressed genes during plant infection2. In the present study, a list of candidate genes previously identified in the transcripts of a specialized tissue (pharyngeal gland cells) involved in the nematode parasitism were selected for functional characterization under ROS conditions. In silico analysis of all candidate genes showed that these genes putatively encode for proteins with signal peptide and no transmembrane domain, suggesting secretion during the infection. In the oxidative stress assays4, some of these candidate genes were upregulated after 24h exposure to a natural oxidative agent (hydrogen peroxide) stimulus, in comparison with the expression of the antioxidant enzyme catalase, which directly degrades hydrogen peroxide to water and oxygen. Overall, our results suggest that some of these genes might have a potential role in ROS scavenging activity during plant parasitism of B. xylophilus.