Three R2R3-MYB transcription factors regulate distinct floral pigmentation patterning in Phalaenopsis spp.

Orchidaceae are well known for their fascinating floral morphologic features, specialized pollination, and distinctive ecological strategies. With their long-lasting flowers of various colors and pigmentation patterning, Phalaenopsis spp. have become important ornamental plants worldwide. In this study, we identified three R2R3-MYB transcription factors PeMYB2, PeMYB11, and PeMYB12. Their expression profiles were concomitant with red color formation in Phalaenopsis spp. flowers. Transient assay of overexpression of three PeMYBs verified that PeMYB2 resulted in anthocyanin accumulation, and these PeMYBs could activate the expression of three downstream structural genes Phalaenopsis spp. Flavanone 3-hydroxylase5, Phalaenopsis spp. Dihydroflavonol 4-reductase1, and Phalaenopsis spp. Anthocyanidin synthase3. In addition, these three PeMYBs participated in the distinct pigmentation patterning in a single flower, which was revealed by virus-induced gene silencing. In the sepals/petals, silencing of PeMYB2, PeMYB11, and PeMYB12 resulted in the loss of the full-red pigmentation, red spots, and venation patterns, respectively. Moreover, different pigmentation patterning was regulated by PeMYBs in the sepals/petals and lip. PeMYB11 was responsive to the red spots in the callus of the lip, and PeMYB12 participated in the full pigmentation in the central lobe of the lip. The differential pigmentation patterning was validated by RNA in situ hybridization. Additional assessment was performed in six Phalaenopsis spp. cultivars with different color patterns. The combined expression of these three PeMYBs in different ratios leads to a wealth of complicated floral pigmentation patterning in Phalaenopsis spp.
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