Isolation and identification of MYB transcription factors (MYB19Long and MYB19Short) involved in raised spot anthocyanin pigmentation in lilies (Lilium spp.)

Abstract

Although anthocyanin color patterns on flowers are among the most attractive characteristics, the genetic mechanisms through which color patterns are developed are not well understood, especially for color patterns associated with altered petal structure. Lilium species and cultivars often develop raised spots, where the interior surfaces of tepals increase to develop bumps with accompanying anthocyanin accumulation. The aim of this study was to identify transcription factors regulating pigmentation of the bumps. We identified two R2R3-MYB genes, MYB19Long and MYB19Short, in Lilium leichtlinii, L. lancifolium, and Asiatic hybrid lily cultivars. Their amino acid sequences were similar; however, part of the C-terminal region was triplicated in MYB19Long. Spatial and temporal expression profiles in lilies were strongly associated with anthocyanin biosynthesis gene expression in the bumps, and some defects were found in these genes in L. lancifolium ‘Pure Gold’ that developed colorless bumps. Thus, both MYB19Long and MYB19Short were likely to be involved in the bump pigmentation. MYB19Long had a stronger ability to stimulate target gene expression than MYB19Short, and expression levels of MYB19Long were greater than those of MYB19Short in lily tepals; thus, the ability to biosynthesize anthocyanin pigments was greater for MYB19Long than for MYB19Short. Among the F1 population, MYB19Short expression was found only in the tepals of F1 plants that developed bumps, although all of the F1 plants possessed the MYB19Short gene, indicating that MYB19 expression followed bump development. These findings helped to elucidate the genetic mechanisms underlying raised spot development.