Abstract
BackgroundPine trees challenged by Bursaphelenchus xylophilus invasion produce phytoalexins to combat this nematode. Nevertheless, the phytoalexins of Asian pine trees are ineffective against B. xylophilus. The anti-phytoalexin genes of B. xylophilus disable almost all Asian pine phytoalexins, which has allowed B. xylophilus to devastate pine forests in eastern Asia over the last four decades. However, to date, the factors that stimulate anti-phytoalexin gene expression and the mechanisms by which these genes act are not well understood.ResultsHere, we described anti-phytoalexin genes in B. xylophilus using transcriptomic and bioinformatics analyses. The genes that were induced by both Pinus massoniana and carvone and had similarly elevated expression trends were considered anti-phytoalexin genes. Altogether, 187 anti-phytoalexin genes were identified, including 4 cathepsin genes. KEGG pathway enrichment indicated that those cathepsins were related to the Lysosome pathway. Since cathepsins help to maintain metabolic homeostasis by participating in the degradation of heterophagic and autophagic material, the lysosomal cathepsin gene Bx-cathepsin W was cloned and characterized. The results of the RNAi assessment indicated that the knockdown of Bx-cathepsin W reduced the survival rates of B. xylophilus under carvone or P. massoniana stress. The correlation between Bx-cathepsin W and the susceptibility of pines showed that Bx-cathepsin W might help improve the anti-phytotoxin ability of B. xylophilus.ConclusionsThe results indicated that the anti-phytoalexin gene Bx-cathepsin W supported the survival of B. xylophilus under P. massoniana phytoalexin stress. The cDNA library sequencing, differentially expressed gene identification, and WGCNA algorithm analysis provided insight at a systemic level into the gene regulation of B. xylophilus in response to the immune reaction of P. massoniana. These results will lead to a better understanding of the function of nematode defenses in host innate immunity.
Highlights
Pine trees challenged by Bursaphelenchus xylophilus invasion produce phytoalexins to combat this nematode
This study presents our investigations into the mechanism of B. xylophilus against phytoalexin and the molecular characterization of a Bx-cathepsin W gene
Clean reads were mapped to the reference genome, the result showed that more than 93% of the transcripts could mapping to the reference genome (Additional file 1: Table S1) [9]
Summary
Pine trees challenged by Bursaphelenchus xylophilus invasion produce phytoalexins to combat this nematode. The pine wood nematode Bursaphelenchus xylophilus, the causative agent of a devastating epidemic of pine wilt disease, is a migratory endoparasite that causes severe damage to pine forests in East Asia and Europe [1, 2]. In both the nematode’s native habitat in North America and in new epidemic areas in East Asia and Europe, B. xylophilus has Susceptible host plants are not completely vulnerable because their immune system can combat the vast majority of attackers [4]. This study presents our investigations into the mechanism of B. xylophilus against phytoalexin and the molecular characterization of a Bx-cathepsin W gene
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