Altered monoterpene composition in transgenic mint following the introduction of 4S-limonene synthase

Genetic transformation of Mentha arvensis and M. × piperita with the neomycine phosphotransferase marker gene and a 4S-limonene synthase cDNA from M. spicata led to the regeneration of 47 transformed plants. In these plants, integration of the transgene was checked by PCR and Southern blots. Transcripts were detected by RT-PCR and monoterpene profiles were determined by gas chromatography. Quantitative and qualitative modifications in monoterpene levels were observed in both M. arvensis and M. × piperita transgenic plants. Four M. × piperita transgenic plants contained higher levels of total monoterpenes, whereas monoterpene levels were lower in two M. arvensis transgenic lines. In both M. × piperita and M. arvensis transgenic lines, altered levels of compounds formed directly from geranyl diphosphate such as cineole or ocimene and monoterpene end-products such as pulegone or piperitone were observed. These effects were consistent with either over-expression or co-suppression of the 4S-ls gene, depending on the transgenic line. These data demonstrate the feasibility of modifying essential oil content by the introduction of a cDNA encoding an enzyme involved in monoterpene metabolism.