Abscisic acid (ABA) is a plant hormone involved in seed development and germination and in responses to various environmental stresses. The last step of ABA biosynthesis involves oxidation of abscisic aldehyde, and aldehyde oxidase (EC ) is thought to catalyze this reaction. An aldehyde oxidase isoform, AOdelta, encoded by AAO3, one of four Arabidopsis aldehyde oxidase genes (AAO1, AAO2, AAO3, and AAO4), is the most likely candidate for the enzyme, because it can efficiently catalyze the oxidation of abscisic aldehyde to ABA. Here, we report the isolation and characterization of an ABA-deficient Arabidopsis mutant that maps at the AAO3 locus. The mutant exhibits a wilty phenotype in rosette leaves, but seed dormancy is not affected. ABA levels were significantly reduced in the mutant leaves, explaining the wilty phenotype in rosettes, whereas the level in the mutant seeds was less reduced. No AOdelta activity could be detected in the rosette leaves of the mutant. Sequence data showed that the mutant contains a G to A substitution in the AAO3 gene. The mutation causes incorrect splicing of the ninth intron of AAO3 mRNA. We thus conclude that the ABA-deficient mutant is impaired in the AAO3 gene and that the gene product, AOdelta, is an aldehyde oxidase that catalyzes the last step of ABA biosynthesis in Arabidopsis, specifically in rosette leaves. Other aldehyde oxidases may be involved in ABA biosynthesis in other organs.

译文

脱落酸 (ABA) 是一种植物激素,参与种子发育和发芽以及对各种环境胁迫的响应。ABA生物合成的最后一步涉及脱落酸醛的氧化,醛氧化酶 (EC) 被认为可以催化该反应。由四个拟南芥醛氧化酶基因 (AAO1,AAO2,AAO3和AAO4) 之一的AAO3编码的醛氧化酶同工型AOdelta是该酶的最可能候选者,因为它可以有效地催化脱落酸醛向ABA的氧化。在这里,我们报告了定位在AAO3基因座的ABA缺陷型拟南芥突变体隔离和表征。该突变体在玫瑰花结叶片中表现出枯萎表型,但种子休眠不受影响。突变叶片中的ABA水平显着降低,这解释了玫瑰花结中的wilty表型,而突变种子中的水平降低较少。在突变体的莲座丛叶中未检测到AOdelta活性。序列数据表明,该突变体在AAO3基因中含有一个G到a的取代。该突变导致AAO3 mRNA第九个内含子的不正确剪接。因此,我们得出结论,ABA缺陷型突变体在AAO3基因中受损,并且基因产物AOdelta是一种醛氧化酶,可催化拟南芥 (特别是莲座叶) 中ABA生物合成的最后一步。其他醛氧化酶可能参与其他器官的ABA生物合成。

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