Two distinct dihydroflavonol 4-reductases involved in anthocyanin biosynthesis in Gerbera Hybrids

Gerbera hybrids are important cut flowers sold worldwide. Beside carotenoids in yellow inflorescenses, they are known to synthesize various anthocyanins giving orange, red and pink colors. Different varieties accumulating either pelargonidin (Pg) or cyanidin (Cy) derivatives or even both together have been described. Dihydroflavonol 4-reductase (DFR) is known as the key enzyme in anthocyanin biosynthesis and a gene coding for the respective protein was cloned and functionally characterized in vitro and in planta from the pink variety “Regina” (1, 2). From these studies it became apparent that the recombinant protein accepts both, dihydrokaempferol (DHK) and dihydroquercetin (DHQ), as substrates enabling the synthesis of Pg and Cy derivatives, respectively. The availability of DHQ depends on the activity of flavonoid 3’-hydroxylase (F3’H), a membrane bound cytochrome P450 protein, which was also cloned and characterized from the same variety (3). Moreover, the genetics of this step is also described. However, in vivo inhibition of F3’H by applying the specific inhibitor tetcyclacis resulted in white segments of the Cy-line “Clivia” which led to the assumption that the DFR in this specific variety is not able to convert DHK into the precursors of Pg-derivatives and therefore has different catalytical characteristics compared to the “Regina” DFR.