Metabolome analysis and functional characterization reveals that d-gluconic acid contributes to pine defence against Bursaphelenchus xylophilus infection.

Pines (Pinus L.) are widely cultivated for their rich resin content and ease of wood processing. However, pines are constantly threatened by pine wood nematode (PWN; Bursaphelenchus xylophilus), causing a large number of pine forests to wilt and die. Pinus massoniana and P. thunbergii are both major host species for PWN. Previous studies have found that P. thunbergii is more sensitive to PWN than P. massoniana. It is particularly important to understand the differential sensitivity mechanisms against PWN among pine species in order to ensure their balanced growth and protect their diversity. Therefore, this study analyzed and identified the main differential metabolic pathway between P. massoniana and P. thunbergii through metabolomics. We compared the disease phenotypes of P. massoniana and P. thunbergii inoculated with PWN. And we further analyzed metabolome data to screen the different resistance pathways in the two pine species. As a result, the pentose phosphate pathway, in which d-gluconate was the key difference substance, was prominent in the resistance difference of P. massoniana and P. thunbergii. The levels of G6DPH, NADPH and organic acids in P. massoniana were significantly higher than those in P. thunbergii to better maintain redox balance. The content of these substances in P. thunbergii increased after treatment with exogenous d-gluconic acid, and its ability to resist nematodes was comparable to that of P. massoniana. Moreover, d-gluconic acid was demonstrated by scanning electron microscopy to restore the damage of pine cells. This discovery indicated that activating the pentose phosphate pathway could increase the ability of pine trees to defend against nematodes, which not only enhances the understanding of pine resistance, but also promotes breeding research on pine trees and provides a novel perspective for the development of new insecticidal substances.