Differential effects of rapamycin on Bursaphelenchus xylophilus with different virulence and differential expression of autophagy genes under stresses in nematodes

Pine wilt disease (PWD) caused by the pine wood nematode (PWN), Bursaphelenchus xylophilus, is a devastating disease for Pinus spp. The virulence and resilience of PWN are closely linked to the spread and development of PWD. Numerous studies have shown that Autophagy has important physiological and pathological functions in eukaryotes. But little is known about the relationships between Autophagy and PWNs' virulence and resistance. In this study, through observation under the microscope and recording, we found the induction of Autophagy by rapamycin could dramatically improve movement ability of PWNs with different virulence, and the highly virulent AMA3 isolate moved more than the low virulent YW4 isolate when Autophagy was over-induced. High concentrations of rapamycin substantially improved the feeding and reproduction of AMA3 but not YW4. Conserved domains of Autophagy genes BxATG3, BxATG4, and BxATG7 were first cloned from PWNs by reverse transcription-polymerase chain reaction (RT-PCR). Expression profiling of these three Autophagy genes under biotic and abiotic stresses in PWNs with different virulence was determined by quantitative RT-PCR. The results revealed the expression levels of these three Autophagy genes in PWNs with different virulence were increased significantly when nematodes were subject to high and low temperatures, oxidative stress, and defensive responses of pine trees. The expression levels of Autophagy genes under biotic and abiotic stresses in AMA3 were higher than those in YW4, and different genes showed different performance. Our study clarified that Autophagy was closely related to virulence and resistance of PWN, and the ability of a highly virulent isolate to regulate Autophagy activity under stresses was stronger than that of a low virulent isolate.