Abstract:

Using headspace solid–phase microextraction（HS–SPME），gas chromatography–mass spectrometry（GC–MS）and quantitative real-time PCR techniques，we analyzed the biochemical and genetic characterization of the metabolic pathway on fragrance emission of Lilium longiflorum × Asiatic hybrids（LA）. Five interspecific Lilium hybrids cultivars were collected to analyze the differences in scent emissions including Lilium longiflorum × Asiatic hybrids，Longiflorum hybrids，Asiatic hybrids and Oriential hybrids × Trumpet hybrids. These five cultivars were divided into three levels：non-scented，light-scented，and strong-scented. Three key genes of the mevalonic acid（MVA）pathway were isolated from LA hybrids by the homology cloning. The results indicated that there were significant differences in the release of floral scent components in five lily hybrids with different levels of fragrance，and the emitted regulation of terpene compounds was consistent with the degree of perceptible fragrance. The aroma content of‘Freya’reached the maximum in the early flowering period，and the aroma content of tepal was the highest among the four floral tissues. The expression patterns of enzyme genes（HMGR，MVD，FPS and TPS）in the MVA pathway were different in different interspecific lily cultivars. The expression level of TPS was consistent with the emitted regulation of terpene compounds on the flowering of‘Freya’，which indicated that TPS played a pivotal role in the volatilization of terpene compounds. We obtained a terpene synthase gene named as LlaTPS in LA hybrids‘Freya’，which was the final step in the MVA pathway. The full length of the cDNA was 1 799 bp，with an open reading frame of 1 764 bp，encoding a total of 587 amino acids. The phylogenetic tree analysis showed that LlaTPS was the closest to the monoterpene synthase of Lilium hybrid cultivar‘Siberia’，and belonged to TPSb subfamily. LlaFPPS was cloned from LA hybrids‘Freya’，which can catalyze farnesyl diphosphate（FPP）as the precursor for sesquiterpene. The full length of the cDNA was 1 072 bp，with an open reading frame of 1 056 bp，encoding a total of 351 amino acids. The phylogenetic tree analysis showed that LlaFPPS encoding protein had a close relationship with monocotyledons plant FPPS protein，and far more distant from leguminous plants. LlaMVD（KX034060）was isolated from LA hybrids‘Freya’，which was the key gene in the MVA pathway. The full length of the cDNA was 1 439 bp，with an open reading frame of 1 275 bp，encoding a total of 424 amino acids. The phylogenetic tree analysis showed that Lilium MVD is closely related to that of Elaeis guineensis and Oryza brachyantha.

Key words: lily, Lilium longiflorum ×, Asiatic hybrids, floral scent, TPS, FPPS, MVD