A Research On Color Formation And Color-related Genes Of Grape Hyacinth (Muscari) Flowers

To elucidate the material bases and physico-chemical factors associated with bluepigmentation of grape hyacinth, nine Muscari cultivars with a gradation of blue color fromdark to light were used as materials and four white cultivars were served as controls tosystemically investigate the properties of flower perianths, including petal structures,anthocyanin, flavonol contents, pH value and metal ion contents. Moreover, transcriptomeanlaysis was performed on M. armeniacum and its white variant. Based on the putativecolor-related genes from the transcriptomic database and metabolite profiling of Muscariflowers, metabolic pathways of flower pigmentation were elucidated, and the key candidategenes that determining the loss of pigmentation in white flowers of M. armeniacum were alsospeculated. The main results are described as follows:1. Anthocyanin and flavonols in13Muscari flowers were detected using Highperformance liquid chromatography (HPLC) and the results indicated that the main flowerpigments were delphinidin (Del) and its derivatives (Petunidin), cyanidin (Cy) and itsderivatives (Cyanidin-galactoside, Cyanidin-rutin). Among the detected pigments, the bluepigmentation is attributable the Del plays critical roles in blue formation, while Cy contributesto the reddish hues. Myricetin (My) and Dihydromyricetin (DHM) potentially function asco-pigmentations to involve in the blue color formation of grape hyacinths. Elementmeasurement showed that the concentrations of Ca2+and Fe3+in blue perianths are relativehigher than that in white or purple one, which could promote the blue color formation ofgrape hyacinths. There are no significnant differences in perianth anatomical structure,epidermal cell shape, distribution pattern of pigment and the sap pH among different Muscariflowers. Although these factors could subtly regulate the flower color, but they were not thekey factors in controling the blue pigmentation of grape hyacinths.2. Based on the color related metabolite profiling, a metabolic pattern of Muscari flowerpigmentation was preliminary drawn. Moreover, the metabolic flux and productive forces ofeach sub-network were systemically evaluated and the core role of delphinidin metabolism inthe pigmentation/depigmentation of grape hyacinth was determined.3. RNA-Seq analysis was performed on M. armeniacum and its white variant. A total of90,477unigenes were obtained,143of which were putative homologs to color-related genes based on functional annotation. Combined with chemical analysis and bioinformatics, themetabolic pathways related to Muscari flower pigmentation were elucidated.4. An integrative approach to investigate the flower-color variation mechanisms was setup through a combination of transcriptome sequencing and metabolite analysis. Moreover, anew hypothesis explaining the lack of color phenotype in grape hyacinth flower was proposed.The competition alteration of the substrate between flavonol synthase (FLS) anddihydroflavonol4-reductase (DFR) may lead to blue pigmentation elimination while themulti-shunt from the limited flux in the Cy synthesis pathway seems to be the most likelyreason for the color change in the white flowers of M. armeniacum.