| Summary: | <i>Pinus densiflora</i> is an important pine species in Northeast Asia due to its historical, cultural, and economic values. Pine wood nematode (PWN) seriously damages <i>P. densiflora,</i> causing the pine wilt disease (PWD). Changes of phyto-compounds in resin and monoterpenes in <i>P. densiflora</i> after infection of PWN were studied. The changes were identified by GC-MS in control and infected <i>P. densiflora</i>. Among the resin phytochemicals (in <i>P. densiflora</i>), 3-carene was distinctly enhanced after PWN inoculation. The emitted plant volatile monoterpenes were analyzed by HS-SPME/GC-MS. It was observed that the amount of 3-carene enhanced conspicuously after infection of PWNs in both <i>P. densiflora</i> and <i>P. koraiensis</i> at 9.7 and 54.7 times, respectively. 3-Carene synthase gene (<i>Pd3-cars</i>) of <i>P. densiflora</i> was isolated and functionally characterized by transgenic tobacco overexpressing <i>Pd3-cars</i>. Integration and expression of transgenic tobacco were confirmed by genomic and RT-PCR analysis. The <i>Pd3-cars</i> gene was expressed in transgenic tobacco plants. Furthermore, the production of 3-carene was identified by HS-SPME/GC-MS analysis as the volatile compounds emitted from leaves of transgenic tobacco. Treatment of 3-carene to PWNs showed a mild nematicidal activity with 45.98% mortality at the concentration of 10 mg/mL. The current findings may apply to the early diagnosis of pine wilt disease infected by PWNs through enhanced emission of 3-carene.
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