Molecular cloning and expression analysis of a monoterpene synthase gene involved in floral scent production in lily (Lilium ‘Siberia’)

Lilium ‘Siberia’ flowers produce a strong scent, with monoterpenes serving as the main volatile component. Using a homology-based PCR strategy, we cloned a monoterpene synthase gene (LiTPS) from Lilium ‘Siberia’ petals. The gene consisted of a 1761-bp open reading frame, and encoded a 587-amino acid protein. The deduced amino acid sequence contained a highly conserved DDxxD domain at the C-terminus and RRx₈W motifs at the N-terminus, which are both characteristic features of terpene synthase genes. Additionally, LiTPS was 40–50% similar to already known monoterpene synthases from other plants. Phylogenetic analysis of LiTPS revealed that it belonged to the TPS-b terpene synthase subfamily. LiTPS was predicted to contain an organelle-targeting peptide and function as a monoterpene synthase in plastids. Analyses of the structure of LiTPS suggested that it is a Class III terpene synthase gene. Furthermore, LiTPS was highly expressed in petals, but almost undetectable in stamens, styles, and leaves. During floral development in Lilium ‘Siberia’ plants, LiTPS was expressed in mature flower buds, with the highest expression levels registered on day 4 after anthesis (i.e., with fully open flowers), followed by a gradual decrease in expression levels. To the best of our knowledge, this is the first report describing cloning a Lilium terpene synthase gene. We report a positive correlation between the LiTPS expression level and floral scent component emission rate. This study provides potentially useful information for future research into the possible roles of LiTPS in the monoterpene metabolic pathway.