The microRNA828/MYB12 module is involved in bicolor pattern development in Asiatic hybrid lily (Lilium spp.) flowers

Some Asiatic hybrid lily cultivars develop bicolor tepals, which consist of anthocyanin-pigmented upper half and un-pigmented lower half, and a MYB12, a subgroup 6 member of R2R3-MYB positively regulating anthocyanin biosynthesis, is down-regulated at the lower half. However, MYB12 usually expresses over entire tepal regions in many lily cultivars and why MYB12 of bicolor cultivars shows spatially different expression in a single tepal remains unclear. As the lily MYB12 mRNA included putative binding sites for microRNA, the involvement of microRNA in the spatially different accumulation of MYB12 transcripts was evaluated. We isolated low molecular weight RNA from lower and upper halves of Lollypop tepals at stage 4, processed them into sequencing libraries using adapted Illumina protocols, and clarified small RNA sequences. Then, we screened microRNA that interacted with MYB12 mRNA, and also analyzed secondary siRNA derived from MYB12 transcripts. In the bicolor tepals, mature miR828 was more highly accumulated at the lower half than the upper half and miR828-directed cleavage of MYB12 transcripts was found predominantly in the lower half. Moreover, the cleavage triggered the production of secondary siRNA from MYB12 transcripts and these siRNA accumulated predominantly in the lower half. Thus, we concluded that miR828 suppressed the MYB12 transcript accumulation and the miR828/MYB12 module had a crucial role in the bicolor pattern development in lily flowers.