Integrated transcriptomic and metabolic analyses reveal the early response mechanism of Pinus tabulaeformis to pine wood nematodes.

Pine wilt disease (PWD) is a devastating disease of pine trees caused by the pine wood nematode (Bursapherenchus xylophilus, PWN). To study how Pinus tabulaeformis responds to PWD infection, we collected 3-year-old P. tabulaeformis seedlings at 2 days, 5 days, and 8 days after being infected with B. xylophilus. We identified genes and metabolites early responding to infection using transcriptome and metabolomic data obtained by high-throughput mRNA sequencing (RNA-seq) and liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based assays, respectively. The following results were obtained: (1) After inoculation with PWN, the average number of days taken for 3-year-old P. tabulaeformis seedlings to develop symptoms was 8 days. (2) Combined transcriptome and metabolome analysis revealed that phenylpropanoid biosynthesis and flavonoid biosynthesis are critically important pathways for P. tabulaeformis to respond to PWD. (3) The response of P. tabulaeformis to stress was mainly through positive regulation of gene expression, including some key genes related to plant hormones or transcription factors that have been widely studied. Genes related to pathways such as photosynthesis, plant-pathogen interactions, and DNA replication were downregulated. (4) Terpenoid biosynthesis genes involved during the development of pine wilt disease. This study demonstrated the defence and pathogenic mechanisms of P. tabulaeformis against PWD, providing a reference for the early diagnosis of PWD.