Induced resistance to pine wilt disease in Pinus massoniana by the endophytic engineered bacterium Pseudomonas koreensis BM06-P60

• Defense gene expression in P. massoniana with BM06-P60 was significantly higher. • BM06-P60 increases POD activity and lowers MDA content, reducing oxidative stress. • BM06-P60 significantly reduces the nematode population within the host. • BM06-P60 enhances P. massoniana resistance to PWD through induction of host defenses. Pine wilt disease (PWD), caused by Bursaphelenchus xylophilus, is a globally devastating forest disease. Endophytic bacteria can improve host resistance to diseases by inducing systemic defense responses. We previously constructed an engineered endophytic bacterium, Pseudomonas koreensis BM06-P60, which expresses the exogenous nematicidal peptidase P60 and achieves a 70 % control efficacy against PWD. In the present study, we aimed to further explore whether BM06-P60 improves the resistance of P. massoniana to PWD by strengthening the intrinsic defense capacity of the host. P. massoniana seedlings were treated with BM06-P60, the wild-type strain BM06, or sterile water as a control and then inoculated with nematodes. Quantitative reverse transcription polymerase chain reaction analysis revealed that BM06-P60 significantly induced the expression of defense-related genes in P. massoniana, including cell wall–associated hydrolase , whose relative expression peaked at 92.62-fold at 12 h postinoculation; Dehydration-responsive protein-encoding gene, which was upregulated 50.90-fold at 48 h; and chitinase , PR-2 family ( β-1,3-glucanase) , and PR-5 family (thaumatin-like proteins), which exhibited 16.21- to 32.94-fold induction between 6 and 12 h. Enzyme activity assays revealed that POD activity in the BM06-P60 treatment group was significantly higher than that in the other two groups, whereas MDA content was the lowest. BM06-P60 treatment significantly reduced the nematode population within the host. In summary, BM06-P60 enhances the resistance of P. massoniana to PWD, providing a theoretical basis for its application in the biological control of the disease.