Flower color and pigmentation patterns in Phalaenopsis orchids

Orchidaceae, one of the largest plant families, is well known for its fascinating floral morphological features, specialized pollination, and distinctive ecological strategies. Phalaenopsis, with its longlasting flowers of various colors, has become important ornamental plants worldwide. However, the molecular mechanism of the anthocyanin biosynthesis is not well studied. In this chapter, the structural and regulatory genes involved in the flower color and anthocyanin biosynthetic pathway are identified and characterized in Phalaenopsis. The expression of three PeMYBs - PeMYB2, PeMYB11, and PeMYB12 - and three structural genes - PeF3H5, PeDFR1, and PeANS3 - was coincident with the anthocyanin accumulation. Transient assay of overexpression of the three PeMYBs verified that PeMYB2 resulted in anthocyanin accumulation, and these PeMYBs could activate the expression of three downstream structural genes, PeF3H5, PeDFR1, and PeANS3. In addition, these three PeMYBs participated in the distinct pigmentation patterning in a single flower, as revealed by virus-induced gene silencing. In the sepals/ petals, the 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 combined expression of these three PeMYBs in different ratios leads to a wealth of complicated floral pigmentation patterning in Phalaenopsis. This study will be beneficial for molecular breeding of new Phalaenopsis cultivars with various floral pigmentation patterns and investigation of the mechanism for many somaclonal variants with changed flower colors.