Differences of Pine Wood Nematode (Bursaphelenchus xylophilus) Developmental Stages under High-Osmotic-Pressure Stress.

Simple Summary: Pine wilt disease is a devastating disease, and its causal pathogen, pine wood nematode (PWN), is extremely challenging to manage. This study identified that PWN enters cryptobiosis under high-osmotic-pressure stress. The phenotypic changes and survival of the nematodes during each developmental stage were significantly different. Among them, the third-stage dispersal juvenile had the highest survival and body length change rates. By comparing the gene expression differences between the third-stage dispersal juvenile and other stages, it was found that they exhibited expression differences in genes in energy compound synthesis and anti-reversal signal pathway. The results of this study provide a theoretical basis for the prevention and treatment of PWN by exploiting the differences in high osmotic pressure tolerance at different developmental stages. Under ion imbalance, water deficiency, and salt stress, the osmotic pressure of the tree sap increases, and pine wood nematodes (Bursaphelenchus xylophilus, PWN) parasitizing in the trees may be subjected to high-osmotic-pressure stress. KCl, L-malic acid, sucrose, and glycerol solutions were used as osmolytes to explore the highest osmotic concentration that PWN can tolerate. Survival analysis showed that when the treatment concentration exceeded 90%, only a few nematodes in the glycerol group survived under 6 h treatment, and most of the survivors were third-stage dispersal juveniles (DJ3). Further examination revealed that under different concentrations of glycerol-induced high osmotic pressure, the survival rate and body length change rate were the highest in the DJ3 and the lowest in the second-stage propagative juveniles. In order to explore the molecular mechanism of resistance of DJ3 to high osmotic stress, transcriptome sequencing was performed at each developmental stage of PWN and differentially expressed genes that were up-regulated or down-regulated only in DJ3 were screened. The expression of genes related to CoA in DJ3, a key enzyme in metabolism, was significantly higher than the other developmental stages. In addition, the expression of the anti-reversal signal pathway-related gene AKT-1 in DJ3 was significantly lower than in the other development stages. Therefore, the specific expression of genes in DJ3 under high osmotic pressure may help them rapidly produce and accumulate energy-related compounds and activate the adenosine 5′-monophosphate (AMP)-activated protein kinase (AMPK) pathway to respond to damage caused by high-osmotic-pressure stress in time, thus promoting survival. [ABSTRACT FROM AUTHOR]