LiCOI1 mediates the biosynthesis of monoterpenes induced by methyl jasmonate in Lilium ‘Siberia’

As a volatile hormone signal, methyl jasmonate (MeJA) can regulate the biosynthesis of secondary metabolites. But in floral fragrance, the effect and mechanisms of MeJA on monoterpenes, the major components of many plants, are largely unknown. In this paper, we measured the release of monoterpenes from petals of Lilium ‘Siberia’ after MeJA treatment, as well as the expressions of monoterpene pathway genes and Lilium coronatine-insensitive (LiCOI1) gene. Then the LiCOI1 gene was cloned, and using virus-induced gene silencing (VIGS) technology, its function in monoterpene biosynthesis in response to MeJA was validated. The results showed that MeJA significantly improved the release amounts of myrcene, ocimene, and linalool. The expression levels of synthase genes [Lilium myrcene synthase (LiMYS), Lilium ocimene synthase (LiOCS), as well as Lilium linalool synthase (LiLIS)], two pathway genes [Lilium 1-deoxy-D-xylulose 5-phosphate synthase (LiDXS) and Lilium 1-deoxy-D-xylulose-5-phosphate reductoisomerase (LiDXR)] were enhanced. Moreover, the LiCOI1 gene exhibited a remarkably increased expression level, which suggested its signaling role. Based on the analysis, the full length of LiCOI1 gene was 1809 bp, whose deduced protein contained 602 amino acids and was mainly located in the nucleus. Silencing the expression of LiCOI1 in petals significantly depressed not only the gene expressions of LiMYS, LiOCS, LiLIS, LiDXS, and LiDXR, but also the release amounts of myrcene, ocimene, and linalool. These results confirm that LiCOI1 plays an important signaling role in MeJA-induced enhancement of monoterpene biosynthesis in Lilium ‘Siberia’.