Full-length transcriptome sequencing and bHLH transcription factor genes expression in Pinus massoniana under feeding pressure of Monochamus alternatus

Pine wood nematode disease (PWD) is a severe condition affecting pines, caused by the pine wood nematode. These nematodes enter healthy host plants through feeding wounds created by pine beetles. Exogenous methyl jasmonate (MeJA) can trigger terpene-based defense responses in conifers, inducing changes in related pathways and stimulating the synthesis and release of terpene compounds. Pinus massoniana (Masson pine) is a key lipid-producing tree in China, but it is also a susceptible host for both pine wood nematode disease and the pine black longiceps beetle. To investigate the response pathways of Masson pine to pine beetle feeding, transcriptome sequencing was performed using Illumina and PacBio Sequel platforms. The analysis revealed differential gene expression in Masson pine shoots under simulated feeding conditions. Seventeen differentially expressed bHLH genes were identified. Gene Ontology (GO) and KEGG pathway enrichment analyses indicated that most of these bHLH transcription factors are involved in secondary metabolite synthesis and plant hormone signaling. Notably, five bHLH transcription factors, which are related to terpenoid synthase synthesis, were highly expressed in Masson pine following simulated feeding.