Light-induced expression of basic helix-loop-helix genes involved in anthocyanin biosynthesis in flowers and leaves of Asiatic hybrid lily

Transcription of anthocyanin biosynthetic genes is usually controlled by transcription factors such as basic-helix-loop-helix (bHLH) and R2R3-MYB. To know the regulatory mechanisms of anthocyanin accumulation in Asiatic hybrid lily (Lilium spp.), cDNA clones encoding bHLH transcription factors were isolated from tepals and their expression was examined in this study. This is the first report about cDNAs for bHLH genes among the species in monocots other than Gramineae. Two cDNAs corresponding to LhbHLH1 and LhbHLH2 genes were isolated; the former encoded the protein having the similarity to AmDELILA and PhJAF13 and the latter one did to PhAN1. LhbHLH1 and LhbHLH2 were expressed in tepals, stems and leaves. In filaments and pistils, only LhbHLH2 was transcribed. During tepal development, transcriptions of LhbHLH genes were always detected, and the peak of LhbHLH2 expression preceded the peak of LhDFR expression. When lily buds were exposed to light, anthocyanin accumulation was induced in leaves and peaked at 4 days after light exposure. The transcription of LhbHLH2 peaked at 2 days after light exposure and decreased after that. LhbHLH1 transcription was affected by light to a lesser extent than LhbHLH2 at 2 days. These expressional changes preceded the change of anthocyanin amount. Similarly in tepals, both anthocyanin amount and the transcription of LhDFR and LhbHLH2 decreased in the dark after 6 days, but LhbHLH1 transcription was not affected. These results suggest that LhbHLH1 and LhbHLH2, especially LhbHLH2, are involved in anthocyanin biosynthesis, and that response to light exposure was different between LhbHLH1 and LhbHLH2.