Abstract
BackgroundRecently, pine wood nematode (PWN, Bursaphelenchus xylophilus) has been found in the extreme cold area of northeast China. The third-stage dispersal juvenile (DJ3) of PWN, which is a long-lived stress-resistant stage, plays an important role in the process of PWN spreading to low-temperature areas, as this stage can survive under unfavorable conditions.ResultsWeighted correlation network analysis (WGCNA) was used to analyze the expression patterns of 15,889 genes included in 21 RNA-Seq results of PWN at DJ3 and the other 6 different stages, and a total of 12 coexpression modules were obtained. Among them, the magenta module has the highest correlation with DJ3, which included a total of 652 genes. KEGG enrichment analysis showed that most of the genes in the magenta module were involved in metabolic processes, which were related to autophagy and longevity regulation. These pathways included starch and sucrose metabolism, which contains trehalose metabolism. To explore the function of trehalose in DJ3 formation and survival under − 20 °C, a trehalose-6-phosphate synthase encoding gene (Bx-tps), a trehalose-6-phosphate phosphatase encoding gene (Bx-tpp) and 7 trehalase encoding genes (Bx-tres) were identified and investigated. The expression of these 9 genes was related to the formation of DJ3. A treatment under − 20 °C induced the accumulation of trehalose. The survival rate of DJ3 at -20 °C reduced after silencing of any of these trehalose metabolism genes. Further analysis suggested that two trehalose synthesis genes were highly correlated with DJ3 and might be involved in autophagy by regulating with energy conversion related genes.ConclusionsThe above results indicated that trehalose metabolism promotes DJ3 formation and helps DJ3 survive at -20 °C. Although trehalose accumulation is favorable for DJ3 to cope with low-temperature stress, multiple trehalose metabolism genes need to work together. There may be a multi-path regulated physiological process involving trehalose synthesis genes under low-temperature stress resistance. This physiological process may regulate the formation and maintenance of DJ3 through autophagy and energy conversion.
Highlights
Pine wood nematode (PWN, Bursaphelenchus xylophilus) has been found in the extreme cold area of northeast China
To explore the pathways related to third-stage dispersal juvenile (DJ3), coexpression modules using the expression data of 15,899 genes from 21 libraries of pine wood nematode (PWN) from different PWN stages (Fig. 2 A) were constructed by applying Weighted correlation network analysis (WGCNA)
The analysis identified that the magenta module was significantly associated with DJ3
Summary
Pine wood nematode (PWN, Bursaphelenchus xylophilus) has been found in the extreme cold area of northeast China. The third-stage dispersal juvenile (DJ3) of PWN, which is a long-lived stress-resistant stage, plays an important role in the process of PWN spreading to low-temperature areas, as this stage can survive under unfavorable conditions. The spread of PWN to low-temperature areas was most likely due to the fact that unlike many other Aphelenchoididae nematodes, PWN has a complex life cycle, including specific stages of development at which it survives in hostile environments. DJ3 accumulates a large number of small lipid droplets in the body, which is a long-lived stressresistant stage, is supposed to play an important role in the northern expansion of this species, as it can survive under unfavorable conditions inside the deadwood of the host tree from autumn to the following spring [4,5,6]. The control of DJ3 should allow for the prevention of the spread of this nematode species
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