Abscisic aldehyde oxidase in leaves of Arabidopsis thaliana

Abstract

SummaryAbscisic acid (ABA) is a plant hormone involved in seed development and responses to various environmental stresses. Oxidation of abscisic aldehyde is the last step of ABA biosynthesis and is catalysed by aldehyde oxidase (EC 1.2.3.1). We have reported the occurrence of three isoforms of aldehyde oxidase, AOa, AOb and AOg, in Arabidopsis thaliana seedlings, but none oxidized abscisic aldehyde. Here we report a new isoform, AOd, found in rosette leaf extracts, which ef®ciently oxidizes abscisic aldehyde. AOd was speci®cally recognized by antibodies raised against a recombinant peptide encoded by AAO3, one of four Arabidopsis aldehyde oxidase genes (AAO1, AAO2, AAO3 and AAO4). Functionally expressed AAO3 protein in the yeast Pichia pastoris showed a substrate preference very similar to that of rosette AOd. These results indicate that AOd is encoded by AAO3. AOd produced in P. pastoris exhibited a very low K m value for abscisic aldehyde (0.51 mM), and the oxidation product was determined by gas chromatography±mass spectrometry to be ABA. Northern analysis showed that AAO3 mRNA is highly expressed in rosette leaves. When the rosette leaves were detached and exposed to dehydration, AAO3 mRNA expression increased rapidly within 3 h of the treatment. These results suggest that AOd, the AAO3 gene product, acts as an abscisic aldehyde oxidase in Arabidopsis rosette leaves.

Two New Alleles of the abscisic aldehyde oxidase 3 Gene Reveal Its Role in Abscisic Acid Biosynthesis in Seeds

“…2C). Using only 5 mg, we could not detect the transcript (in agreement with Seo et al, 2000b). Likewise, in dry seeds we were not able to detect AAO3 mRNA (data not shown); however, upon imbibition and osmotic stress treatment, we could detect it (Fig.…”

“…sre2-2/sre2-2 3 aao3-1/aao3-1 of MoCo is a cofactor of AAO3, and the AAO3 holoenzyme catalyzes the oxidation of the 1-aldehyde group of abscisic aldehyde to the 1-carboxylic acid group, generating ABA (Seo et al, 2000b). The Arabidopsis aldehyde oxidase family comprises four genes: AAO1, AAO2, AAO3, and AAO4 (Seo et al, 2000b).…”

“…The Arabidopsis aldehyde oxidase family comprises four genes: AAO1, AAO2, AAO3, and AAO4 (Seo et al, 2000b). Aldehyde oxidase assays indicated that AAO1, AAO2, and AAO4 had almost no activity using abscisic aldehyde as a substrate (Seo et al, , 2000b.…”

“…Additionally, gene expression studies failed to detect the AAO3 transcript both in siliques and dry seeds from a Col ecotype (Seo et al, 2000b). As both aao3-2 and aao3-3 were isolated in a seed germination screening, we reasoned that AAO3 gene product must contribute to ABA biosynthesis in seeds.…”

“…For instance, aao3-1 seeds (in a Landsberg erecta [Ler] genetic background) do not show a clear change in dormancy (Seo et al, 2000a), whereas other known ABA-deficient mutants have much less dormant seeds. Additionally, Seo et al (2000b) failed to detect AAO3 gene expression in siliques and dry seeds.…”