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

Gerbera hybrids are an important cut flower sold world wide. Beside carotenoids in yellow inflorescence they were know to synthesis various anthocyanins giving orange, red and pink colors. Different varieties are known to accumulate either pelargonidin (Pg) or cyanidin (Cy) derivatives or even both together were 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 characterised in vitro but also in planta from the pink variety "Regina" (1, 2). From these studies it becomes 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 catalytic characteristics compared to the "Regina" DFR. 1.Helariutta Y, Elomaa P, Kotilainen M, Seppänen P, Teeri TH. (1993). Cloning of cDNA coding for dihydroflavonol-4-reductase (DFR) and characterization of dfr expression in the corollas of Gerbera hybrida var. Regina (Compositae). Plant Mol Biol. 22(2): 183-193. 2.Martens S, Teeri T, Forkmann G. (2002). Heterologous expression of dihydroflavonol 4-reductases from various plants. FEBS Lett. 531(3):453-458. 3.Seitz C, Eder C, Deiml B, Kellner S, Martens S, Seitz C (2006). Cloning, functional identification and sequence analysis of flavonoid 3'-hydroxylase and flavonoid 3',5'-hydroxylase cDNAs reveals independent evolution of flavonoid 3',5'-hydroxylase in the Asteraceae family. Plant Mol Biol. 61(3): 365-381.