Stage-specific transcriptome of Bursaphelenchus xylophilus reveals temporal regulation of effector genes and roles of the dauer-like stages in the lifecycle

Suguru E Tanaka,Ryusei Tanaka,Kenji Fukuda,Taisei Kikuchi,Mehmet Dayi,Isheng J Tsai,Mark Bligh,Yasunobu Maeda,Yuko Takeuchi-Kaneko,Natsumi Kanzaki

doi:10.1038/s41598-019-42570-7

Abstract

The pine wood nematode Bursaphelenchus xylophilus is the causal agent of pine wilt disease, one of the most devastating forest diseases in East Asian and West European countries. The lifecycle of B. xylophilus includes four propagative larval stages and gonochoristic adults which are involved in the pathogenicity, and two stages of dispersal larvae involved in the spread of the disease. To elucidate the ecological roles of each developmental stage in the pathogenic life cycle, we performed a comprehensive transcriptome analysis using RNA-seq generated from all developmental stages of B. xylophilus and compared transcriptomes between stages. We found more than 9000 genes are differentially expressed in at least one stage of the life cycle including genes involved in general nematode biology such as reproduction and moulting but also effector genes likely to be involved in parasitism. The dispersal-stage transcriptome revealed its analogy to C. elegans dauer and the distinct roles of the two larval stages from each other regarding survival and transmission. This study provides important insights and resources to understand B. xylophilus parasitic biology.

Highlights

The pine wood nematode, Bursaphelenchus xylophilus, is the causal agent of Pine Wilt Disease (PWD), one of the most serious forest diseases in East Asian and West European countries[1]
Two independent studies using RNA deep sequencing (RNA-seq) to compare the mycetophagous with phytophagous stages revealed that several effector candidate genes including those encoding peptidases, glycosyl hydrolases and detoxification proteins are differentially regulated during the infection[20,22], suggesting transcriptional and physiological changes are important for the parasitism of B. xylophilus
Orthologues in the fourth clusters have high expressions in the egg and/or L2 and relatively low in D3 and D4. Those orthologues in C. elegans mostly show a similar pattern. These results suggest that nematode dauer pathways are largely conserved between C. elegans and B. xylophilus, and B. xylophilus D3 and D4 use different sets of C. elegans dauer genes from each other to form and maintain their special developmental stages

Summary

Introduction

The pine wood nematode, Bursaphelenchus xylophilus, is the causal agent of Pine Wilt Disease (PWD), one of the most serious forest diseases in East Asian and West European countries[1]. Two independent studies using RNA deep sequencing (RNA-seq) to compare the mycetophagous with phytophagous stages revealed that several effector candidate genes including those encoding peptidases, glycosyl hydrolases and detoxification proteins are differentially regulated during the infection[20,22], suggesting transcriptional and physiological changes are important for the parasitism of B. xylophilus. Those RNA-seq studies used mixed-stage nematodes and it remains unclear if each stage has any specific roles in the pathogenic life cycle. We generated transcriptome data for the dispersal (dauer-like) stages for the first time as well as the propagative stages and achieved a comprehensive gene expression profile

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