The promoter sequence of (-)-limonene synthase in Mentha Canadensis and its strong activity in the glandular trichome and in the stomatal guard cells

Mentha Species are well known for their useful essential oils. Limonene synthase is one of the key enzymes in the monoterpene biosynthesis pathway of mint. In this study, qRT-PCR analysis was conducted on various tissues and treatments of Mentha canadensis to reveal the limonene synthase ( McLS) gene expression levels and expression response pattern. The results showed that McLS was highly expressed in young leaves, and induced by light, abscisic acid (ABA), methyl jasmonate (MeJA), NaCl, and mannitol treatments. The (-)-limonene synthase promoter ( proMcLS ) was isolated and its cis elements were analyzed. The upstream region of the (-)-limonene synthase gene contains several cis -acting elements, including the core cis elements of the TATA box and CAAT box, light-responsive motifs, ABA- and MeJA-responsive motifs, and guard cell-specific cis elements. Transcriptional fusion of the proMcLS to the gusA reporter gene was conducted in N . tabacum via Agrobacterium- mediated transformation. Transgenic T0 lines displayed β-glucuronidase histochemical staining activity in short glandular trichomes and the stigma of flowers. No signal was detected from tall glandular trichomes or stomatal guard cells, while T1 lines displayed β-glucuronidase activity in both short glandular trichomes and stomatal guard cells. The transcription factor families binding to the McLS promoter were predicted using PlantPAN 3.0, and transcription factors that were co-expressed with McLS in various light treatments were identified. These data describe a new tissue-specific transcriptional promoter that can be used for metabolic engineering of plants in the future.