PMID:15064374

Citation	Saito, S, Hirai, N, Matsumoto, C, Ohigashi, H, Ohta, D, Sakata, K and Mizutani, M (2004) Arabidopsis CYP707As encode (+)-abscisic acid 8'-hydroxylase, a key enzyme in the oxidative catabolism of abscisic acid. Plant Physiol. 134:1439-49
Abstract	Abscisic acid (ABA) is involved in a number of critical processes in normal growth and development as well as in adaptive responses to environmental stresses. For correct and accurate actions, a physiologically active ABA level is controlled through fine-tuning of de novo biosynthesis and catabolism. The hydroxylation at the 8'-position of ABA is known as the key step of ABA catabolism, and this reaction is catalyzed by ABA 8'-hydroxylase, a cytochrome P450. Here, we demonstrate CYP707As as the P450 responsible for the 8'-hydroxylation of (+)-ABA. First, all four CYP707A cDNAs were cloned from Arabidopsis and used for the production of the recombinant proteins in insect cells using a baculovirus system. The insect cells expressing CYP707A3 efficiently metabolized (+)-ABA to yield phaseic acid, the isomerized form of 8'-hydroxy-ABA. The microsomes from the insect cells exhibited very strong activity of 8'-hydroxylation of (+)-ABA (K(m) = 1.3 microm and k(cat) = 15 min(-1)). The solubilized CYP707A3 protein bound (+)-ABA with the binding constant K(s) = 3.5 microm, but did not bind (-)-ABA. Detailed analyses of the reaction products confirmed that CYP707A3 does not have the isomerization activity of 8'-hydroxy-ABA to phaseic acid. Further experiments revealed that Arabidopsis CYP707A1 and CYP707A4 also encode ABA 8'-hydroxylase. The transcripts of the CYP707A genes increased in response to salt, osmotic, and dehydration stresses as well as ABA. These results establish that the CYP707A family plays a key role in regulating the ABA level through the 8'-hydroxylation of (+)-ABA.
Links	PubMed PMC419820 Online version:10.1104/pp.103.037614
Keywords	Abscisic Acid/metabolism; Abscisic Acid/pharmacology; Animals; Arabidopsis/enzymology; Arabidopsis/genetics; Arabidopsis Proteins/genetics; Arabidopsis Proteins/metabolism; Binding Sites/drug effects; Binding Sites/genetics; Brassinosteroids; Cholestanols/pharmacology; Cloning, Molecular; Cytochrome P-450 Enzyme System/genetics; Cytochrome P-450 Enzyme System/metabolism; DNA, Complementary/chemistry; DNA, Complementary/genetics; Gene Expression Regulation, Enzymologic/drug effects; Gene Expression Regulation, Plant/drug effects; Gibberellins/pharmacology; Insects/genetics; Insects/metabolism; Isoenzymes/genetics; Isoenzymes/metabolism; Microsomes/enzymology; Mixed Function Oxygenases/genetics; Mixed Function Oxygenases/metabolism; Molecular Sequence Data; Multigene Family; Oxidation-Reduction/drug effects; Phylogeny; Plant Growth Regulators/pharmacology; Protein Binding/drug effects; Protein Binding/genetics; Steroids, Heterocyclic/pharmacology
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