Two alcohol dehydrogenases enhance Bursaphelenchus xylophilus resistance in Pinus massonniana via 3-hexenol biosynthesis accumulation.

Abstract

Green leaf volatiles, oxygenated compounds released by plants under biotic and abiotic stresses, play essential roles as signaling molecules in plant immune responses. However, the defense mechanisms mediated by these volatiles remain poorly characterized in conifers, particularly regarding Pinus massoniana against the invasive pine wood nematode (PWN, Bursaphelenchus xylophilus). Here, we systematically integrated transcriptomic and metabolic profiles to compare the defense responses of resistant and susceptible P. massoniana following PWN inoculation. Our results revealed that alpha-linolenic acid metabolism showed a positive response to PWN infection in resistant P. massoniana. Notably, (Z)-3-hexenol and its ester derivatives, along with the key alcohol dehydrogenases (ADH ) genes in the linolenic acid pathway, were significantly activated in resistant P. massoniana at 7 days post-inoculation. Tissue-specific expression profiling of PmADH12 and PmADH13 demonstrated that they were crucial positive regulators in response to PWN challenge in resistant P. massoniana. Functional characterization confirmed that overexpression of PmADHs efficiently increases the production of (Z)-3-hexenol and its ester derivative in P. massoniana. In addition, these PmADHs encode enzymes capable of catalyzing (Z)-3-hexenal to produce (Z)-3-hexenol. Furthermore, in vitro bioassays revealed that (Z)-3-hexenol, the primary enzymatic product of PmADHs, effectively inhibited the PWN survival. Our findings provide mechanistic evidence that ADHs-mediated (Z)-3-hexenol biosynthesis constitutes a chemical defense strategy against PWN infestation in resistant P. massoniana.