The 9-cis-epoxycarotenoid cleavage reaction is the key regulatory step of abscisic acid biosynthesis in water-stressed bean
The 9-cis-epoxycarotenoid cleavage reaction is the key regulatory step of abscisic acid biosynthesis in water-stressed bean
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DOI：
10.1073/pnas.96.26.15354
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发表时间：
1999-12-21
影响因子：
11.1
通讯作者：
Zeevaart, JAD
中科院分区：
文献类型：
--
作者：
Qin, XQ;Zeevaart, JAD
脱落酸（ABA）是类胡萝卜素的裂解产物，参与植物的应激反应。植物对水分胁迫的一个众所周知的反应是ABA的积累，这是由从头合成引起的。植物中ABA生物合成的限制步骤可能是9-顺式环氧类胡萝卜素的裂解。这是ABA生物合成的第一步该步骤生成C-15中间叶黄素和c -25类伪胡萝卜素，cDNA PvNCED1克隆自枯萎豆（Phaseolus vulgaris L.）叶片。PvNCED1全长2398 bp， ORF为615 aa，编码68 kda蛋白。PvNCED1蛋白被导入叶绿体，在叶绿体中与类囊体结合。重组蛋白PvNCED1催化9-顺式紫黄质和9'-顺式新黄质的裂解，因此该酶被称为9-顺式环氧类胡萝卜素双加氧酶。当离体豆叶受到水分胁迫时，ABA积累先于PvNCED1 mRNA和蛋白水平的大幅增加。相反，胁迫叶片的再水化导致PvNCED1 mRNA、蛋白和ABA水平迅速下降。在豆根中，PvNCED1 mRNA、蛋白和ABA水平之间也存在类似的相关性。然而，ABA含量远低于叶片，可能是因为根中的类胡萝卜素前体库比叶片中的小得多。在7℃条件下，PvNCED1 mRNA和ABA被水分胁迫缓慢诱导，但在2℃条件下，两者均未积累。结果表明，干旱诱导的ABA生物合成受9-顺式环氧类胡萝卜素裂解反应的调控，该反应发生在类胡萝卜素底物所在的类囊体中。
Abscisic acid (ABA), a cleavage product of carotenoids, is involved in stress responses in plants. A well known response of plants to water stress is accumulation of ABA, which is caused by de novo synthesis. The limiting step of ABA biosynthesis in plants is presumably the cleavage of 9-cis-epoxycarotenoids. the first committed step of ABA biosynthesis. This step generates the C-15 intermediate xanthoxin and C-25-apocarotenoids, A cDNA, PvNCED1, was cloned from wilted bean (Phaseolus vulgaris L.) leaves. The 2,398-bp full-length PvNCED1 has an ORF of 615 aa and encodes a 68-kDa protein. The PvNCED1 protein is imported into chloroplasts, where it is associated with the thylakoids. The recombinant protein PvNCED1 catalyzes the cleavage of 9-cis-violaxanthin and 9'-cis-neoxanthin, so that the enzyme is referred to as 9-cis-epoxycarotenoid dioxygenase. When detached bean leaves were water stressed, ABA accumulation was preceded by large increases in PvNCED1 mRNA and protein levels. Conversely, rehydration of stressed leaves caused a rapid decrease in PvNCED1 mRNA, protein, and ABA levels. In bean roots, a similar correlation among PvNCED1 mRNA, protein, and ABA levels was observed. However, the ABA content was much less than in leaves, presumably because of the much smaller carotenoid precursor pool in roots than in leaves. At 7 degrees C, PvNCED1 mRNA and ABA were slowly induced by water stress, but, at 2 degrees C, neither accumulated. The results provide evidence that drought-induced ABA biosynthesis is regulated by the 9-cis-epoxycarotenoid cleavage reaction and that this reaction takes place in the thylakoids, where the carotenoid substrate is located.