Yang Seung Hwan, Zeevaart Jan A D
Department of Energy, Plant Research Laboratory, Michigan State University, East Lansing, MI 48824-1312, USA.
Plant J. 2006 Sep;47(5):675-86. doi: 10.1111/j.1365-313X.2006.02815.x. Epub 2006 Jul 19.
In plants, the level of abscisic acid (ABA) is determined by synthesis and catabolism. Hydroxylation of ABA at the 8' position is the key step in ABA catabolism. This reaction is catalyzed by ABA 8'-hydroxylase, a cytochrome P450 (CYP). The cDNAs of PvCYP707A1 and PvCYP707A2 were isolated from bean (Phaseolus vulgaris L.) axes treated with (+)-ABA and that of PvCYP707A3 from dehydrated bean leaves. The recombinant PvCYP707A proteins expressed in yeast were biochemically characterized. Yeast strains over-expressing any of the three PvCYP707As were able to convert ABA to phaseic acid (PA). The microsomal fractions from these yeast strains also exhibited ABA 8'-hydroxylase activity. Expression of PvCYP707A3 in primary leaves was strongly increased by water stress, whereas PvCYP707A1 and PvCYP707A2 mRNA levels were rapidly increased by rehydration of water-stressed leaves. Northern blot analysis of PvCYP707As in bean showed a high level of expression in the mature fruits, senescent leaves, roots, seed coats and axes. All three PvCYP707As were expressed at varying intensities throughout seed development. Imbibed seeds also had high PvCYP707A mRNA levels. Thus, expression of PvCYP707As is both environmentally and developmentally regulated. Transgenic Nicotiana sylvestris plants over-expressing PvCYP707As displayed a wilty phenotype, and had reduced ABA levels and increased PA levels. These results demonstrate that expression of PvCYP707As is the major mechanism by which ABA catabolism is regulated in bean.
在植物中，脱落酸（ABA）的水平由合成和分解代谢决定。ABA在8'位的羟基化是ABA分解代谢的关键步骤。该反应由细胞色素P450（CYP）——ABA 8'-羟化酶催化。PvCYP707A1和PvCYP707A2的cDNA是从用（+）-ABA处理的菜豆（Phaseolus vulgaris L.）轴中分离得到的，而PvCYP707A3的cDNA是从脱水的菜豆叶片中分离得到的。对在酵母中表达的重组PvCYP707A蛋白进行了生化特性分析。过表达三种PvCYP707A中的任何一种的酵母菌株都能够将ABA转化为相酸（PA）。这些酵母菌株的微粒体部分也表现出ABA 8'-羟化酶活性。水分胁迫强烈增加了PvCYP707A3在初生叶中的表达，而水分胁迫叶片复水后，PvCYP707A1和PvCYP707A2的mRNA水平迅速增加。对菜豆中PvCYP707A的Northern印迹分析表明，其在成熟果实、衰老叶片、根、种皮和轴中高水平表达。在种子发育过程中，所有三种PvCYP707A都以不同强度表达。吸胀种子也有较高的PvCYP707A mRNA水平。因此，PvCYP707A的表达受环境和发育的调控。过表达PvCYP707A的转基因野生烟草植株表现出萎蔫表型，ABA水平降低，PA水平升高。这些结果表明，PvCYP707A的表达是菜豆中ABA分解代谢调控的主要机制。
