Cymbidium hybrida dihydroflavonol 4-reductase does not efficiently reduce dihydrokaempferol to produce orange pelargonidin-type anthocyanins

Some angiosperms are limited to a range of possible flower colors. This lim itation can be due to the lack of an anthocyanin biosynthetic gene or to th e substrate specificity of a key anthocyanin biosynthetic enzyme, dihydrofl avonol 4-reductase (DFR). Cymbidium hybrida orchid flowers primarily produc e cyanidin-type (pink to red) anthocyanins and lack the pelargonidin-type ( orange to brick-red) anthocyanins. To investigate the underlying molecular mechanism of this flower color range, we cloned a Cymbidium DFR gene and tr ansformed it into a DFR- petunia line. We found that the Cymbidium DFR did not efficiently reduce dihydrokaempferol (DHK), which is an essential step for pelargonidin production. Phylogenetic analysis of a number of DFR seque nces indicate that the inability to catalyze DHK reduction has occurred at least twice during angiosperm evolution. Our results indicate that developi ng a pelargonidin-type orange flower color in Cymbidium may require the tra nsformation of a DFR gene that can efficiently catalyze DHK reduction.