Flower color is the decisive factor that affects the commercial value of ornamental flowers. Therefore, it is important to study the regulation of flower color formation in lily to discover the positive and negative factors that regulate this important trait. In this study, MYB transcription factors (TFs) were characterized to understand the regulatory mechanism of anthocyanin biosynthesis in lily. Two R2R3-MYB TFs, LvMYB5, and LvMYB1, were found to regulate anthocyanin biosynthesis in lily flowers. LvMYB5, which has an activation motif, belongs to the SG6 MYB protein subgroup of Arabidopsis thaliana. Transient expression of LvMYB5 indicated that LvMYB5 can promote coloration in Nicotiana benthamiana leaves, and that expression of LvMYB5 increases the expression levels of NbCHS, NbDFR, and NbANS. VIGS experiments in lily petals showed that the accumulation of anthocyanins was reduced when LvMYB5 was silenced. Luciferase assays showed that LvMYB5 can promote anthocyanin synthesis by activating the ANS gene promoter. Therefore, LvMYB5 plays an important role in flower coloration in lily. In addition, the transient expression experiment provided preliminary evidence that LvMYB1 (an R2R3-MYB TF) inhibits anthocyanin synthesis in lily flowers. The discovery of activating and inhibitory factors related to anthocyanin biosynthesis in lily provides a theoretical basis for improving flower color through genetic engineering. The results of our study provide a new direction for the further study of the mechanisms of flower color formation in lilies.

Flower color is one of the most important qualitative characteristics of ornamental horticultural plants, which mainly depends on anthocyanins and carotenoids. Modification of flower color in ornamental plants involves many aspects, including complicated structural gens, transcription factors and metabolic pathways. Anthocyanins are important secondary metabolites in the flavonoid biosynthesis pathway, which mainly derive from six anthocyanidins. Anthocyanin has antioxidant activity, protects plants and performs some other functions. Studying the genes and regulatory factors in the biosynthesis pathway will contribute to cultivating novel flower color plants and to improving plants’ resistance. To date, a series of structural and regulatory genes that are involved in anthocyanin synthesis and color formation have been reported, whose functions have also been revealed. Some color-related transgenic flowers have been successfully obtained. Carotenoids are the source of the yellow pigments in the petals of many flowers. The carotenoid biosynthesis pathway as well as its major enzymes and genes are conducive to regulate its biosynthesis via genetic engineering methods and thereby changing the color of flowers. In this paper, we review the plant flower color in terms of mechanisms of plant pigment formation, classification of flower color, biosynthesis pathway, and genes related to anthocyanin formation. Subsequently, we analyze the regulating mechanism of the expression of these genes, including transcription regulation and post-transcription regulation. The methods and achievements in flower color improvement in recent years are summarized. Finally, analyzing the molecular regulatory network in flower color formation provides a theoretical basis for the improvement and modification of flower color.

Background: Petals are the colorful region of many ornamental plants. Quality traits of petal color directly affect the value of ornamental plants. Although the regulatory mechanism of flower color has been widely studied in many plants, that of lily flower color is still worth further exploration.Results: In this study, the pigmentation regulatory network in different regions of the petal of lily cultivar ‘Vivian’ was analyzed through tissue structure, metabolites biosynthesis, and gene expression. We found that cell morphology of the petal in un-pigmented region differed from that in pigmented region. The cell morphology tends to flatten in un-pigmented region where the color is lighter. Moreover, high level anthocyanin was found in the pigmented regions by metabonomic analysis, especially cyanidin derivatives. However, flavanones were accumulated, contrast with anthocyanin in the un-pigmented regions of lily petal. To understand the relationship of these different metabolites and lily flower color, RNA-Seq was used to analyze the differentially expressed genes-related metabolite biosynthesis. Among these genes, the expression levels of several genes-related cyanidin derivatives biosynthesis were significantly different between the pigmented and un-pigmented regions, such asLvMYB5, LvMYB7, LvF3’H, LvDFR, LvANSandLv3GT.Conclusions: This data will help us to further understand the regulation network of lily petal pigmentation and create different unique color species.