Comprehensive isolation and expression analysis of the flavonoid biosynthesis-related genes in Tricyrtis spp.

Tricyrtis spp., which belong to the family Liliaceae, produce unique flowers, whose tepals have many reddish-purple spots. Although elucidation of a molecular mechanism of tepal spot formation and molecular breeding for flower colour alteration are desired for Tricyrtis spp., only one flavonoid biosynthesis-related gene, TrCHS encoding chalcone synthase (CHS), has been isolated so far. In the present study, comprehensive isolation and expression analysis of the other flavonoid biosynthesis-related genes were carried out in Tricyrtis sp. Six genes (TrCHI, TrF3H, TrF3’H, TrFLS, TrDFR, and TrANS) encoding biosynthetic enzymes chalcone isomerase (CHI), flavanone-3-hydroxylase (F3H); flavonoid 3’-hydroxylase (F3’H), flavonol synthase (FLS), dihydroflavonol 4-reductase (DFR), and anthocyanin synthase (ANS) as well as three genes (TrMYB1, TrbHLH2 and TrWDR) encoding transcription factors myeloblastosis 1 (MYB1), basic helix-loop-helix (bHLH), and WD40 repeats (WDRs) were newly isolated. Phylogenetic analysis showed that each isolated gene was classified into the monocotyledonous clade. Deduced amino acid sequences of DFRs showed that TrDFR has no substrate specificity. “Early” genes in the flavonoid biosynthetic pathway (TrCHS, TrCHI, and TrF3H) were constantly expressed in tepals during flower development, whereas expressions of “late” genes (TrF3’H, TrFLS, TrDFR, and TrANS) varied with the flower developmental stage. Expression patterns of the late genes were mostly correlated with those of transcriptional factor genes, indicating that the late genes may be under the control of a transcription factor complex consisted of TrMYB1, TrbHLH2, and TrWDR. Accumulation of anthocyanins in tepals occurred slightly after transcriptional upregulation of the late genes. Results obtained in the present study may be valuable for further studies on flower colour and flower colour pattern in Tricyrtis spp.