cDNA cloning of abscisic aldehyde oxidase in Arabidopsis and Nicotiana

醛氧化酶（AO）在动物和微生物中得到了广泛的研究。然而，在植物中，关于这种酶的信息非常有限。对这种酶的极大兴趣在于它可能参与脱落酸（ABA）的生物合成。本研究从拟南芥中克隆了4个AO全长cdna，研究了它们的生理功能，并对烟叶AO进行了纯化和鉴定。结果总结如下：(1)从拟南芥中获得4个不同的AO cDNA克隆。他们的产物通过对拟南芥中4种AOs的抗体进行分析。(2)将这4个AO cdna导入酵母毕赤酵母中，产物在酵母细胞中功能表达。结果表明，两个AO基因在拟南芥幼苗中编码三个AO，另一个AO基因在叶片中产生一个AO。利用酵母中表达的AO进行的生化研究表明，叶片AO是催化脱落醛氧化生成ABA的最有可能候选AO。(3)而部分纯化的白桦叶AO对脱落醛的偏好非常弱。这一结果与拟南芥的结果相结合，表明拟南芥叶片中可能存在另一种AO，参与ABA的生物合成。

Aldehyde oxidase (AO) has been extensively investigated in animals and microorganisms. In plants, however, there was only a limited information on this enzyme. A great interest in this enzyme has been in its possible involvement in abscisic acid (ABA) biosynthesis. In the present study, we cloned four full-length AO cDNAs from Arabidopsis thaliana and investigate their physiological functions, and we purified and characterized a leaf AO of Nicotiana plumbaginifolia. The summary of the results are as follows ;(1) Four different putative AO cDNA clones were obtained from A.thaliana. Their products were analyzed by using antibodies each specific to four AOs in A.thaliana.(2) The four AO cDNAs were introduced into yeast Pichia pastoris and the products were functionally expressed in the yeast cells. The result revealed that two AO genes encoded three AOs in A.thaliana seedlings and another AO gene produced a leaf AO.Biochemical studies using AOs expressed in yeast indicated that leaf AO is a most possible candidate of an AO that catalyzes oxidation of abscisic aldehyde to form ABA.(3) However, partially purified N.plumbaginifolia leaf AO showed a very weak preference to abscisic aldehyde. This result with combination of the results from A.thaliana suggests that there might be present another AO in N.plumbaginifolia leaves, which involves in ABA biosynthesis.