title: ABA 9'-hydroxylation is catalyzed by CYP707A in Arabidopsis.
abstract: Abscisic acid (ABA) catabolism is important for regulating endogenous ABA levels. To date, most effort has focused on catabolism of ABA to phaseic acid (PA), which is generated spontaneously after 8'-hydroxylation of ABA by cytochrome P450s in the CYP707A subfamily. Neophaseic acid (neoPA) is another well-documented ABA catabolite that is produced via ABA 9'-hydroxylation, but the 9'-hydroxylase has not yet been defined. Here, we show that endogenous neoPA levels are reduced in loss-of-function mutants defective in CYP707A genes. In addition, in planta levels of both neoPA and PA are reduced after treatment of plants with uniconazole-P, a P450 inhibitor. These lines of evidence suggest that CYP707A genes also encode the 9'-hydroxylase required for neoPA synthesis. To test this, in vitro enzyme assays using microsomal fractions from CYP707A-expressing yeast strains were conducted and these showed that all four Arabidopsis CYP707As are 9'-hydroxylases, although this activity is minor. Collectively, our results demonstrate that ABA 9'-hydroxylation is catalyzed by CYP707As as a side reaction.
authors.affiliation: RIKEN Plant Science Center, 1Tsurumi-ku, Yokohama, Japan.
authors.forename: Masanori
authors.initials: M
authors.lastname: Okamoto
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Kushiro
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Jikumaru
authors.forename: Suzanne R
authors.initials: SR
authors.lastname: Abrams
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kamiya
authors.forename: Motoaki
authors.initials: M
authors.lastname: Seki
authors.forename: Eiji
authors.initials: E
authors.lastname: Nambara
mesh_terms: D000040:Abscisic Acid / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D002384:Catalysis; D003577:Cytochrome P-450 Enzyme System / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D015394:Molecular Structure; D010940:Plant Proteins
chemical_list: D010940:Plant Proteins; D000040:Abscisic Acid; D003577:Cytochrome P-450 Enzyme System; C107203:abscisic acid 8'-hydroxylase