Expression of the Thaumatin-Like Protein-1 Gene (Bx-tlp-1) from Pine Wood Nematode Bursaphelenchus xylophilus Affects Terpene Metabolism in Pine Trees.

Abstract

Pine wilt disease is a major forest disease worldwide, including in China, where it has severely damaged pine forest ecosystems, and the pathogen is pine wood nematode (Bursaphelenchus xylophilus). The thaumatin-like protein-1 gene (Bx-tlp-1) is a key gene associated with B. xylophilus pathogenicity, which is also responsive to α-pinene. In this study, an examination of Pinus massoniana seedlings infected by B. xylophilus revealed that monoterpene (sesquiterpene) levels peaked on days 15 and 27 (days 18 and 27). Meanwhile, P. massoniana Pm-tlp expression levels were high on days 3, 12, and 27, which were consistent with the expression of key enzymes genes in the terpene biosynthesis pathway. The functional similarity of B. xylophilus Bx-TLP-1 and P. massoniana Pm-TLP suggests Bx-TLP-1 and Pm-TLP may have similar roles in P. massoniana. There was also no secondary accumulation of terpenes in P. massoniana seedlings during B. xylophilus treated with dsRNA targeting Bx-tlp-1 (dsTLP1) infections, reflecting the decreased pathogenicity of B. xylophilus and the delayed disease progression in pine trees. And the results of micro-CT showed that the degree of cavitation for the trees inoculated with Bx-TLP-1 (0.3811 mm3) was greater than that for the trees inoculated with dsTLP1 PWNs (0.1204 mm3) on day 15 after inoculation. Results from this study indicated that B. xylophilus Bx-tlp-1 gene may induce the upregulated expression of related genes encoding enzymes in the terpene synthesis pathway of P. massoniana, resulting in the accumulation of terpenes, which also provided an insight to investigate the B. xylophilus pathogenicity in the future.