Abstract
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.
Highlights
Lilies are bulbous perennials with large flowers that are fragrant, brightly colored and highly desired by consumers
The luciferase activities were not significantly different between the 35S:LvMYB5 + ANSp1-Luc and 35S:LvMYB5 + ANS gene promoter (ANSp)-Luc treatments, and both of them were much higher than in any of the other treatments. These results indicate that the MYB binding sites in the –1,200 to – 900 bp region of ANSp may be the main LvMYB5 binding sites; LvMYB5 can increase the activity of the promoter to induce gene expression and in turn promote the synthesis of anthocyanins in petal tissue
We found that the LvMYB5 transcription factors (TFs), which contains conserved R2 and R3 domains and an activation domain, functions as an activator of the anthocyanin biosynthesis pathway in lily flowers (Figure 3B)
Summary
Lilies are bulbous perennials with large flowers that are fragrant, brightly colored and highly desired by consumers. The overexpression of AtMYB3/4/7/32, members of A. thaliana MYB gene family subgroup 4 (SG4), inhibit the synthesis of anthocyanins (Chen et al, 2019), showing that they are negative regulators of pigmentation (Kranz et al, 1998). In this study, we analyzed the regulatory effects of two different MYB genes in lily flower pigmentation to reveal the molecular regulatory mechanisms that play roles in lily flower color formation. This will give us a better understanding of the development and regulation of flower color in lily and other ornamental plants
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