Bursaphelenchus xylophilus is fatal to the pine trees around the world. The production of the pine tree secondary metabolite gradually increases in response to a B. xylophilus infestation, via a stress reaction mechanism(s). α-pinene is needed to combat the early stages of B. xylophilus infection and colonization, and to counter its pathogenesis. Therefore, research is needed to characterize the underlying molecular response(s) of B. xylophilus to resist α-pinene. We examined the effects of different concentrations of α-pinene on the mortality and reproduction rate of B. xylophilus in vitro. The molecular response by which B. xylophilus resists α-pinene was examined via comparative transcriptomics of the nematode. Notably, B. xylophilus genes involved in detoxification, transport, and receptor activities were differentially expressed in response to two different concentrations of α-pinene compared with control. Our results contribute to our understanding of the molecular mechanisms by which B. xylophilus responds to monoterpenes in general, and the pathogenesis of B. xylophilus.

Background: The pine wood nematode (PWN;Bursaphelenchus xylophilus) is the most damaging biological pest in pine forest ecosystems in China. However, the pathogenic mechanism remains unclear. Tracheid cavitation induced by excess metabolism of volatile terpenes is a typical characteristic of pine trees infected byB. xylophilus. β-pinene, one of the main volatile terpenes, influences PWN colonization and reproduction, stimulating pathogenicity during the early stages of infection. To elucidate the response mechanism of PWN to β-pinene, pathogenesis, mortality, and reproduction rate were investigated under different concentrations of β-pinene using a transcriptomics approach.Results: A low concentration of β-pinene (BL, C < 25.74 mg/ml) inhibited PWN reproduction, whereas a high concentration (BH, C > 128.7 mg/ml) promoted reproduction. Comparison of PWN expression profiles under low (BL, 21.66 mg/ml) and high (BH, 214.5 mg/ml) β-pinene concentrations at 48 h identified 659 and 418 differentially expressed genes (DEGs), respectively, compared with controls. Some key DEGs are potential regulators of β-pinene via detoxification metabolism (cytochrome P450, UDP-glucuronosyltransferases and short-chain dehydrogenases), ion channel/transporter activity (unc and ATP-binding cassette families), and nuclear receptor -related genes. Gene Ontology enrichment analysis of DEGs revealed metabolic processes as the most significant biological processes, and catalytic activity as the most significant molecular function for both BL and BH samples. Kyoto Encyclopedia of Genes and Genomes (KEGG) Orthology (KO) analysis showed that xenobiotics biodegradation and metabolism, carbohydrate metabolism, lipid metabolism, amino acid metabolism, metabolism of cofactors and vitamins, and transport and catabolism were the dominant terms in metabolism categories.Conclusion: In addition to detoxification via reduction/oxidation (redox) activity, PWN responds to β-pinene through amino acid metabolism, carbohydrate metabolism, and other pathways including growth regulation and epidermal protein changes to overcome β-pinene stress. This study lays a foundation for further exploring the pathogenic mechanism of PWN.

The pinewood nematode (PWN) Bursaphelenchus xylophilus is a forestry quarantine pest and causes an extremely dangerous forest disease that is spreading worldwide. Due to the complex pathogenic factors of pine wood nematode disease, the pathogenesis is still unknown. B. xylophilus ultimately invades a host and causes death. However, little is known about the defence-regulating process of host pine after infection by B. xylophilus at the molecular level. Therefore, we wanted to understand how Pinus massoniana regulates its response to invasion by B. xylophilus. P. massoniana were artificially inoculated with B. xylophilus solution, while those without B. xylophilus solution were used as controls. P. massoniana inoculated with B. xylophilus solution for 0 h, 6 h, 24 h, and 120 h was subjected to high-throughput sequencing to obtain transcriptome data. At various time points (0 h, 6 h, 24 h, 120 h), gene transcription was measured in P. massoniana inoculated with PWN. At different time points, P. massoniana gene transcription differed significantly, with a response to early invasion by PWN. According to Gene Ontology (GO) classification and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, P. massoniana response to PWN invasion involves a wide range of genes, including plant hormone signal transformation, flavonoid biosynthesis, amino sugar and nucleoside sugar metabolism, and MAPK signalling pathways. Among them, inoculation for 120 hours had the greatest impact on differential genes. Subsequently, weighted gene coexpression network analysis (WGCNA) was used to analyse transcriptional regulation of P. massoniana after PWN infection. The results showed that the core gene module of P. massoniana responding to PWN was “MEmagenta”, enriched in oxidative phosphorylation, amino sugar and nucleotide sugar metabolism, and the MAPK signalling pathway. MYB family transcription factors with the highest number of changes between infected and healthy pine trees accounted for 20.4% of the total differentially expressed transcription factors. To conclude, this study contributes to our understanding of the molecular mechanism of initial PWN infection of P. massoniana. Moreover, it provides some important background information on PWN pathogenic mechanisms.

The pinewood nematode (PWN; Bursaphelenchus xylophilus) is the causal agent of pine wilt disease, which results in severe ecological and economic losses in coniferous forests. During overwintering, PWNs undergo morphological and physiological changes to adapt to low temperature environments. Here, the physiological changes of the PWN populations sampled in the summer and winter were compared to analyze the role in response to low temperature. The PWN overwinters as third-stage dispersal juveniles, which showed significantly greater survival rates than summer populations (propagative forms) at subzero temperatures. The major biochemical compounds in the populations were analyzed by gas chromatography. Eight dominant fatty acids, with stearic acid being the most important, were identified from PWN propagative stage and third-stage dispersal stage. Compared with the propagative stage, the dispersal stage showed significant increases in the fatty acid content and the proportion of unsaturated fatty acids. Three carbohydrates trehalose, glycerol and glucose were detected in the PWN. Compared with the summer population, the levels of trehalose and glycerol increased significantly, while glucose decreased, in the winter population. The modifications in fatty acid composition and cryoprotectant levels, as elements of its changing physiology, play important roles in the overwintering success of the PWN.