Arabidopsis thaliana expresses a second functional flavonol synthase

Arabidopsis thaliana L. produces flavonoid pigments, i.e.. avonols, anthocyanidins and proanthocyanidins, from dihydro flavonol substrates. A small family of putative flavonol synthase (FLS) genes had been recognized in Arabidopsis, and functional activity was attributed only to FLS1. Nevertheless, other FLS activities must be present, because A. thaliana fls1 mutants still accumulate significant amounts of. avonols. The recombinant FLSs and leucoanthocyanidin dioxygenase (LDOX) proteins were therefore examined for their enzyme activities, which led to the identification of FLS3 as a second active FLS. This enzyme is therefore likely responsible for the formation of. avonols in the ldox/fls1-2 double mutant. These double mutant and biochemical data demonstrate for the first time that LDOX is capable of catalyzing the in planta formation of. avonols. (C) 2009 Federation of European Biochemical Societies. Published by Elsevier B. V. All rights reserved.