| Summary: | Cembranoids produced by tobacco glandular trichomes have bioactivities in resistance to insect pests and pathogens. Cembratrien-ol synthase (CBTS) plays a key role in the biosynthesis of cembranoids and directly determines the cembranoid content in tobacco. This study examined the effect of changing <i>CBTS1</i> expression on tobacco resistance to the insect pest <i>Spodoptera frugiperda</i> and oomycete pathogen <i>Phytophthora nicotianae</i>. The CDS sequence of <i>CBTS1</i> was cloned into gene overexpression and silencing vectors and introduced into tobacco (<i>Nicotiana tabacum</i> L. cv. TN90) to obtain <i>CBTS1</i>-overexpression plants (CBTS1-OE) and <i>CBTS1</i>-silenced plants (CBTS1-RI). Compared with control plants, the content of cembratrien-ol (CBT-ol) was increased 4.48 times in the CBTS1-OE plants but decreased by 68% in the CBTS1-RI plants, while that of cembratrien-diol (CBT-diol) was increased 3.17 times in the CBTS1-OE plants but decreased by 76% in the CBTS1-RI plants. The <i>S. frugiperda</i> resistance of transgenic tobacco plants was evaluated by in vitro toxicity test, and the results showed that the resistance of CBTS1-OE plants to <i>S. frugiperda</i> was significantly improved but that of CBTS1-RI plants was reduced. The <i>P. nicotianae</i> resistance of transgenic tobacco plants was assessed by the detached leaf assay, and the results showed that the resistance of CBTS1-OE plants to <i>P. nicotianae</i> was enhanced, while that of CBTS1-RI plants was attenuated. Further gene expression analysis showed that overexpression of <i>CBTS1</i> increased the expression of the pathogen-related gene <i>PR-1a</i>, while silencing of <i>CBTS1</i> decreased its expression. This study demonstrated that manipulating the expression of <i>CBTS1</i> could change the cembranoid content in tobacco plants and alter their resistance to both insect pests and oomycete pathogens.
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