Medicago sativa cDNAs Encoding Chalcone Reductase

CHR is an enzyme that co-acts with CHS to produce a branch in the first step of the flavonoid pathway. CHS acting alone catalyzes the sequential coupling of three ma-lonyl-COA molecules with coumaroyl-COA to produce 4,2’,4’,6’-tetrahydroxychalcone (Heller and Hahlbrock, 1980). However, in the presence of CHR and NADPH the oxygen function of the polyketide intermediate, which would produce the 6’-hydroxyl of the chalcone, is reduced and then eliminated as water prior to cyclization, resulting in the formation of 4,2’,4’-trihydroxychalcone (6’-de-oxychalcone). This chalcone is the precursor of the 5-deoxy series of flavonoids and isoflavonoids (Harborne, 1988), which includes nodulation induction factors as well as pterocarpan phytoalexins of the Legu-minosae

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