Application of RNA Interference in the Pinewood Nematode, Bursaphelenchus xylophilus

The pinewood nematode, Bursaphelenchus xylophilus, is one of the most destructive invasive species worldwide, causing the wilting and eventual death of pine trees. Despite the recognition of their economic and environmental significance, it has thus far been impossible to study the detailed gene functions of plant-parasitic nematodes (PPNs) using conventional forward genetics and transgenic methods. However, as a reverse genetics technology, RNA interference (RNAi) facilitates the study of the functional genes of nematodes, including B. xylophilus. This paper outlines a new protocol for RNAi of the ppm-1 gene in B. xylophilus, which has been reported to play crucial roles in the development and reproduction of other pathogenic nematodes. For RNAi, the T7 promoter was linked to the 5'-terminal of the target fragment by polymerase chain reaction (PCR), and double-stranded RNA (dsRNA) was synthesized by in vitro transcription. Subsequently, dsRNA delivery was accomplished by soaking the nematodes in a dsRNA solution mixed with synthetic neurostimulants. Synchronized juveniles of B. xylophilus (approximately 20,000 individuals) were washed and soaked in dsRNA (0.8 µg/mL) in the soaking buffer for 24 h in the dark at 25 °C. The same quantity of nematodes was placed in a soaking buffer without dsRNA as a control. Meanwhile, another identical quantity of nematodes was placed in a soaking buffer with green fluorescent protein (gfp) gene dsRNA as a control. After soaking, the expression level of the target transcripts was determined using real-time quantitative PCR. The effects of RNAi were then confirmed using microscopic observation of the phenotypes and a comparison of the body size of the adults among the groups. The current protocol can help advance research to better understand the functions of the genes of B. xylophilus and other parasitic nematodes toward developing control strategies through genetic engineering.