Comparative Floral Composition And Transcriptome Analysis Between Different Species And Varieties Of Lilac

Flowers fragrance is one of the quality indicators of ornamental plants,attracting pollinators and seed dispersers and playing an important role in the spice and flavor industry.The lilac is a woody aromatic plant of temperate origin,with high ornamental value and economic value.It has a strong fragrance,beautiful and elegant flowers.Lilac is resistant to drought,cold and salt.Leaves and flowers have medicinal benefits that can be processed into perfume and tea.It is an ideal tree for landscaping and in Shandong province it is also an important ornamental tree with high market demand.Investigations of chemical components of lilac floral fragrance and related regulatory mechanism of floral fragrance formation can provide scientific support for the in-depth studies of lilac functions,which has been a hot spot in the field of lilac research in recent years.However,studies on integrative studies of floral fragrance components and transcriptome analysis in lilac petals are relatively rare,limiting the identification of genes related to floral fragrance formation.In this study,two representative species of the genus Lilac-Syringa oblata(with light and fragrant aroma)and Syringa vulgaris(with strong and fragrant aroma),were selected for investigations.To be specific,the traditional variety-Syringa oblata ’AZDX 2018003’(Z03),the newly bred variety-Syringa oblata ’Zi Kui’(ZK),the traditional variety-Syringa vulgaris’ Ci Lan’(CL)and the newly bred variety-Syringa vulgaris ’Li Fei’(LF)were used as experimental materials.The petal samples were firstly analyzed via headspace-solid phase microextraction(HS-SPME)and gas chromatography-mass spectrometry(GC-MS)for the collection and relative quantification of volatile components.Petal samples were then analyzed via transcriptome sequencing to compare the differentially expressed genes and enrichment patterns among different lilac species and varieties.The expression patterns of the target genes were validated in different varieties using real-time quantitative PCR.Furthermore,we performed a preliminary validation of the target lilac TPS gene in tobacco via transient expression.Pre-analysis revealed that simultaneous comparison of the four lilac varieties was poorly reproducible,with large differences in aroma composition,making analyses difficult.Therefore,this study was focused on two comparisons,with one group of comparison was performed between the traditional and newly bred varieties of Syringa oblata(Z03 vs ZK;comparison between varieties within the same genus),and another was performed between newly bred cultivars of Syringa oblata and Syringa vulgaris(ZK vs LF;comparison between different genus).The results are as follows:1.A total of 43 volatile components were identified by comparing the aromatic components and their relative contents of petals between ZK and LF.Terpenoids were the most abundant volatile components in the petals of the two varieties.Terpenoids accounted for 76.9 %in ZK and 60 % in LF,respectively.There were 10 common substances in ZK and LF,of which9 substances were higher in ZK,including 7 terpenes,1 alcohol and 1 alkane.The content of 1substance was higher in LF,which was an ester substance.3 volatile substances were unique to ZK,and 30 volatile substances were unique to LF.2.A total of 6411 differentially expressed genes were obtained by transcriptome sequencing of ZK and LF petals.Compared with ZK,4327 genes were up-regulated and 2084 genes were down-regulated in LF;among them,ubiquinone and other terpene quinone biosynthetic genes were significantly enriched.Correlation analysis of volatile materials and transcriptional data showed that terpene synthase genes(TPS),geranylgeranyl pyrophosphate synthase genes(GGPPS)and 3-hydroxy-3-methylglutaryl-Co A synthase genes(HMGS)were the key genes that lead to differences in floral components of two varieties of lilac,and played important roles in the secondary metabolic pathway of floral components of lilac.3.By comparing traditional variety-Syringa oblata Z03 with the newly bred variety-Syringa oblata ZK and analyzing the aromatic components of the petals and their relative contents,a total of 30 volatile components were identified,with the most abundant volatile substances being the olefin terpenes;66.7% of the olefin terpenes in Z03 and 84.6% in ZK.Three substances were common in Z03 and ZK,of which two kinds of terpenes were higher in ZK while one kind of ester is more abundant in Z03.And there were 12 volatile metabolites specific to Z03 and 10 volatile metabolites specific to ZK.4.Transcriptome sequencing was performed on the petals of Z03 and ZK,and 5113 differentially expressed genes were obtained.Compared with Z03,2118 genes were upregulated and 2995 genes were down-regulated in ZK.The combined analysis of volatile metabolome and transcriptome found that TPS and farnesyl pyrophosphate synthase genes(FPPS)were main genes leading to the difference in floral aroma components between the two cultivars.5.The expression patterns of target genes identified in above studies,such as TPS and HMGS,were validated in different varieties using real-time quantitative PCR.Subsequently,the TPS genes were transiently expressed into tobacco leaves and the altered volatiles were analyzed relative to the control(empty vector),in an attempt to provide a preliminary validation of gene function.This study aims to provide a theoretical and experimental basis for the exploitation of lilac aroma,deepen the understanding of the aroma regulation mechanism of lilac,and help to improve the aroma quality of lilac via metabolic engineering in long term.