White with partially pink flower color in Lilium cernuum var. album is caused by transcriptional regulation of anthocyanin biosynthesis genes

Lilium cernuum is among the most important wild species used for the breeding of Asiatic hybrid lilies. Two flower-color types are included in L. cernuum: the entire tepals are pink in the selected common type, whereas var. album flowers develop white tepals with partially pink regions. To understand the mechanisms creating the white with partially pink tepals, expression of genes related to anthocyanin biosynthesis was investigated. Although the amounts of anthocyanin pigments were considerably lower in the tepals of var. album than in those of the common type, they both expressed the identical LcMYB12 transcription factor gene. We found this gene to positively regulate the expression of anthocyanin biosynthesis genes in the transient assay (agroinfiltration) using tobacco leaves. Expression levels of LcMYB12 and anthocyanin biosynthesis genes were lower in var. album than in the common type. Thus, down-regulation of LcMYB12 expression is likely to be the main reason for the creation of the white with partially colored tepals. The var. album also possessed a non-functional allele of LcMYB12, LcMYB12-del, in which the C-terminal region was truncated. However, the segregation analysis conducted using F-1 plants derived from the crosses between the common type and var. album indicated that LcMYB12-del expression was not correlated with tepal colors. Lilium cernuum developed tiny spots at the base of its tepals. In addition to LcMYB12, LcMYBSPLATTER was expressed at the spot-containing tepal region. Because the LcMYBSPLATTER sequence was very similar to the sequence of LhMYBSPLATTER (formerly LhMYB12-Latvia) regulating the pigmentation at splatter-type anthocyanin spots, LhMYBSPLATTER in Asiatic hybrid lilies is likely to have been derived from L. cemuum.