Re E B, Jones D, Learned R M
Section of Molecular and Cellular Biology, University of California, Davis 95616, USA.
Plant J. 1995 May;7(5):771-84. doi: 10.1046/j.1365-313x.1995.07050771.x.
In eukaryotes, all isoprenoid compounds share a common precursor, mevalonic acid, whose synthesis is catalyzed by the enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase. As one step towards a better understanding of the role that this enzyme plays in coordinating isoprenoid biosynthesis in plants, Arabidopsis thaliana HMG CoA reductase was ectopically expressed in transgenic Arabidopsis plants. By using this molecular genetic approach, several novel and fundamental observations have been made regarding isoprenoid biosynthesis in Arabidopsis. First, it was demonstrated that the overexpression of authentic Arabidopsis HMG CoA reductase is not sufficient to alter the bulk synthesis and accumulation of the abundant end products of the plant isoprenoid pathway. Second, active transcription of the transgene appears to co-activate and deregulate expression of the native gene, resulting in a striking elevation of HMG CoA reductase mRNA levels. Finally, although very high levels of HMG CoA reductase mRNA were expressed in these transgenic plants, only modest increases in enzyme activity could be detected. Taken together, these data suggest that HMG CoA reductase expression is regulated at multiple levels in plants as well as animals, and they provide a foundation for elucidating the molecular mechanisms for mevalonate regulation in A. thaliana.
在真核生物中，所有类异戊二烯化合物都有一个共同的前体——甲羟戊酸，其合成由3-羟基-3-甲基戊二酰辅酶A（HMG CoA）还原酶催化。作为更好地理解该酶在协调植物类异戊二烯生物合成中所起作用的第一步，拟南芥HMG CoA还原酶在转基因拟南芥植物中异位表达。通过使用这种分子遗传学方法，已经对拟南芥中的类异戊二烯生物合成有了一些新颖且基础的观察结果。首先，已证明真实的拟南芥HMG CoA还原酶的过表达不足以改变植物类异戊二烯途径丰富终产物的大量合成和积累。其次，转基因的活性转录似乎共同激活并解除对天然基因表达的调控，导致HMG CoA还原酶mRNA水平显著升高。最后，尽管在这些转基因植物中表达了非常高水平的HMG CoA还原酶mRNA，但只能检测到酶活性有适度增加。综上所述，这些数据表明HMG CoA还原酶的表达在植物以及动物中受到多层次调控，并且它们为阐明拟南芥中甲羟戊酸调控的分子机制提供了基础。
