Metabolic engineering of essential oil yield and composition in mint by altering expression of deoxyxylulose phosphate reductoisomerase and menthofuran synthase

Peppermint(Mentha x piperita L..) was independently transformed with a homo logous sense version of the 1-deoxy-D-xylulose-5-phosphate reductoisomerase cDNA and with a homologous antisense version of the menthofuran synthase c DNA, both driven by the CaMV 35S promoter. Two groups of transgenic plants were regenerated in the reductoisomerase experiments, one of which remained normal in appearance and development; another was deficient in chlorophyll production and grew slowly. Transgenic plants of normal appearance and gro wth habit expressed the reductoisomerase transgene strongly and constitutiv ely, as determined by RNA blot analysis and direct enzyme assay, and these plants accumulated substantially more essential oil (about 50% yield increa se) without change in monoterpene composition compared with wild-type. Chlo rophyll-deficient plants did not afford detectable reductoisomerase mRNA or enzyme activity and yielded less essential oil than did wild-type plants, indicating cosuppression of the reductoisomerase gene. Plants transformed w ith the antisense version of the menthofuran synthase cDNA were normal in a ppearance but produced less than half of this undesirable monoterpene oil c omponent than did wild-type mint grown under unstressed or stressed conditi ons. These experiments demonstrate that essential oil quantity and quality can be regulated by metabolic engineering. Thus, alteration of the committe d step of the mevalonate-independent pathway for supply of terpenoid precur sors improves flux through the pathway that leads to increased monoterpene production, and antisense manipulation of a selected downstream monoterpene biosynthetic step leads to improved oil composition.