title: The Arabidopsis ABA-deficient mutant aba4 demonstrates that the major route for stress-induced ABA accumulation is via neoxanthin isomers.
abstract: A novel abscisic acid (ABA)-deficient mutant, aba4, was identified in a screen for paclobutrazol-resistant germination. Compared with wild-type, the mutant showed reduced endogenous ABA levels in both dehydrated rosettes and seeds. Carotenoid composition analysis demonstrated that the defective locus affects neoxanthin synthesis. The ABA4 gene was identified by map-based cloning, and found to be a unique gene in the Arabidopsis genome. The predicted protein has four putative helical transmembrane domains and shows significant similarity to predicted proteins from tomato, rice and cyanobacteria. Constitutive expression of the ABA4 gene in Arabidopsis transgenic plants led to increased accumulation of trans-neoxanthin, indicating that the ABA4 protein has a direct role in neoxanthin synthesis. aba4 mutant phenotypes were mild compared with previously identified ABA-deficient mutants that exhibit vegetative tissue phenotypes. Indeed, ABA levels in seeds of aba4 mutants were higher than those of aba1 mutants. As aba1 mutants are also affected in a unique gene, this suggests that ABA can be produced in the aba4 mutant by an alternative pathway using violaxanthin as a substrate. It appears, therefore, that in Arabidopsis both violaxanthin and neoxanthin are in vivo substrates for 9-cis-epoxycarotenoid dioxygenases. Furthermore, significantly reduced levels of ABA were synthesized in the aba4 mutant on dehydration, demonstrating that ABA biosynthesis in response to stress must occur mainly via neoxanthin isomer precursors.
authors.affiliation: Laboratoire de Biologie des Semences UMR204, INRA, INAPG, Institut Jean-Pierre Bourgin, F-78026 Versailles cedex, France. helen.north@versailles.inra.fr
authors.forename: Helen M
authors.initials: HM
authors.lastname: North
authors.forename: Aurélie
authors.initials: A
authors.lastname: De Almeida
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Boutin
authors.forename: Anne
authors.initials: A
authors.lastname: Frey
authors.forename: Alexandra
authors.initials: A
authors.lastname: To
authors.forename: Lucy
authors.initials: L
authors.lastname: Botran
authors.forename: Bruno
authors.initials: B
authors.lastname: Sotta
authors.forename: Annie
authors.initials: A
authors.lastname: Marion-Poll
mesh_terms: D000040:Abscisic Acid / Q000235:genetics* / Q000378:metabolism*; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D002338:Carotenoids / Q000235:genetics*; D002736:Chloroplasts / Q000235:genetics; D017124:Conserved Sequence; D018744:DNA, Plant / Q000235:genetics / Q000302:isolation & purification; D017353:Gene Deletion; D005838:Genotype; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D013466:Sulfurtransferases / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D018744:DNA, Plant; D011993:Recombinant Fusion Proteins; D002338:Carotenoids; D000040:Abscisic Acid; C440026:ABA3 protein, Arabidopsis; D013466:Sulfurtransferases