Seo M, Koiwai H, Akaba S, Komano T, Oritani T, Kamiya Y, Koshiba T
Department of Biological Sciences, Tokyo Metropolitan University, Hachioji-shi, Tokyo 192-0397, Japan.
Plant J. 2000 Aug;23(4):481-8. doi: 10.1046/j.1365-313x.2000.00812.x.
Abscisic 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, AOalpha, AObeta and AOgamma, in Arabidopsis thaliana seedlings, but none oxidized abscisic aldehyde. Here we report a new isoform, AOdelta, found in rosette leaf extracts, which efficiently oxidizes abscisic aldehyde. AO delta was specifically 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 AOdelta. These results indicate that AOdelta is encoded by AAO3. AOdelta produced in P. pastoris exhibited a very low Km value for abscisic aldehyde (0.51 microM), 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 AOdelta, the AAO3 gene product, acts as an abscisic aldehyde oxidase in Arabidopsis rosette leaves.
脱落酸（ABA）是一种参与种子发育以及植物对各种环境胁迫响应的植物激素。脱落醛的氧化是ABA生物合成的最后一步，由醛氧化酶（EC 1.2.3.1）催化。我们已经报道了拟南芥幼苗中存在醛氧化酶的三种同工型，AOα、AOβ和AOγ，但它们均不能氧化脱落醛。在此，我们报道在莲座叶提取物中发现的一种新的同工型AOδ，它能高效氧化脱落醛。针对由拟南芥醛氧化酶四个基因之一（AAO1、AAO2、AAO3和AAO4）编码的重组肽制备的抗体能特异性识别AOδ。在酵母毕赤酵母中功能表达的AAO3蛋白表现出与莲座叶AOδ非常相似的底物偏好性。这些结果表明AOδ由AAO3编码。在毕赤酵母中产生的AOδ对脱落醛的Km值非常低（0.51微摩尔），通过气相色谱 - 质谱法测定氧化产物为ABA。Northern分析表明AAO3 mRNA在莲座叶中高度表达。当莲座叶被摘下并暴露于脱水条件下时，AAO3 mRNA表达在处理后3小时内迅速增加。这些结果表明，AOδ即AAO3基因产物，在拟南芥莲座叶中作为脱落醛氧化酶发挥作用。
