| Lavandula angustifolia Mill.,a perennial plant belongs to the lavandula,Lamiaceae,with the essential oil endowing its highly commercial value.Here,volatile terpenoid profiles of individual florets at different developmental stages of lavender were analysed by GC-MS.Transcriptome sequencing and weighted gene coexpression network analysis(WGCNA)carried on the analysis of terpenoids metabolism regulation networks.Olfaction bioassays carried on verifying the terpenoids component to pollinator attraction or herbivore defense.This study elucidates the relationship between gene regulation network,terpenoids composition and ecological function,revealing the molecular mechanism underlying the regulation of volatile terpenoids and the influence on the flower-visiting insects,also providing support for molecular breeding of lavender.The results show as follows:1.56 compounds were identifified by GC-MS analysis in essential oil of samples from the initial flower buds(FBO)and the remote-whorl florets of the first and second axes at five developmental stages(FFDSFSA).As confirmed by clustering and principal component analysis(PCA)of the profiling data,which showed that the essential oil composition of FBO was most abundant(55 compounds).A higher proportion of β-trans-ocimene(20.57%)and(+)-(R)-limonene(17.00%)were characteristic of FBO’s essential oil.With the blossom in turn,the fluctuation of the volatile terpenoids displayed a regular change at each axis,with linalool(17.06%-43.72%),linalyl acetate(19.35%～32.24%)and lavandulyl acetate(11.60%～24.46%)as the main components.2.In the Y-tube olfactometer bioassay,β-trans-ocimene and(+)-(R)-limonene showed a significant phobotaxis to aphids,as well as essential oil of FBO,resulting that the lavender can prevent further damage caused by herbivores.For assays of bees,essential oil of blooming florets,linalyl acetate and lavandulyl acetate exhibit attraction to pollinator(bees).3.Transcriptome sequencing was performed in samples from FBO and FFDSFSA.Approximately 261 G high-quality clean data and 159,337 unigenes were obtained.Through functional annotation and differential expression analysis,9,246 differentially expressed genes were obtained,including 46 genes in the terpenoid synthesis pathway,among which the BOS(Ocimene synthase),SabS1(sabinene synthase),PINS(Pinene synthase)and TEPS(α-terpineol synthase)not been reported in literature;35 terpenoid transporters,1 12 cytochrome P450 hydroxylases and 64 flowering-associated genes were also obtained.The gene expression patterns were related only to the flowering period,and not to the position of the floret(axis 1 or axis 2).4.9246 differentially expressed genes were systematically grouped into 21 gene co-expression modules using WGCNA.Through the KEGG enrichment analysis of the network module,the correlation analysis between the module and terpenoid components,and the flowering period,the most significant enrichment module 16 was obtained.23 and 34 genes for terpenoid biosynthesis and CYP450s,9 TFs and 29 genes related to flowering,13 genes for transport were obtained.Many candidates involved in flowering time and terpenoid biosynthesis,modification and transport were interconnected,suggesting that the gene regulation network controlling the following myriad emissions of volatile terpenoids connected with the fine-tuning blossom.Above studies show that the terpenoids and gene regulation network of initial flower buds exhibiting ecological value in pest control.The precise control of each-axis flowering and regular emissions at transcriptional and metabolic level are important to pollinators attraction for lavender.Our study reveals the relevance between time-series dynamics of flowering and the synthesis and release of terpenoids,which has laid a foundation for the further research of metabolic regulation mechanism of terpenoids and molecular breeding of lavender. |
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