Learned R M, Connolly E L
University of California, Section of Molecular and Cellular Biology, Davis 95616, USA.
Plant J. 1997 Mar;11(3):499-511. doi: 10.1046/j.1365-313x.1997.11030499.x.
Although the coordinated biosynthesis of isoprenoid compounds is thought to be essential to the normal processes of plant growth and development, the mechanisms that regulate the mevalonate pathway in plants are not well understood. As the first committed step in the pathway, the conversion of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) to mevalonic acid by HMG CoA reductase and the regulation of the genes encoding this enzyme have been implicated in the network that controls isoprenoid biosynthesis in higher plants. Using histochemical staining for beta-glucuronidase, as well as conventional RNA hybridization analysis, the temporal and spatial regulation of HMG1, one of the genes encoding HMG CoA reductase in the crucifer Arabidopsis thaliana, has been characterized. Furthermore, the HMG1 promoter is shown to be differentially responsive to illumination in different organs, and promoter activation by light deprivation is confined primarily to immature leaves. In contrast, expression of the HMG1 gene in roots is confined to the elongation zone and is not responsive to illumination. Light-mediated regulation of HMG1 expression is shown to be an organ-autonomous response that depends on direct illumination, and environmental cues regarding light do not appear to be exchanged between different organs in Arabidopsis. These studies reveal several new features of HMG1 regulation, and indicate that the high levels of HMG CoA reductase expression detected in immature leaves may be primarily attributed to the dark-induced expression of HMG1, and that HMG1 is expressed at low levels throughout the plant in response to light. Thus, environmental cues interact with the developmental program to define the pattern of HMG1 gene expression in Arabidopsis.
尽管类异戊二烯化合物的协同生物合成被认为对植物生长和发育的正常过程至关重要，但调节植物甲羟戊酸途径的机制仍未得到充分了解。作为该途径的第一个关键步骤，3-羟基-3-甲基戊二酰辅酶A（HMG CoA）通过HMG CoA还原酶转化为甲羟戊酸，以及编码该酶的基因的调控，已被认为参与了高等植物中控制类异戊二烯生物合成的网络。利用β-葡萄糖醛酸酶的组织化学染色以及传统的RNA杂交分析，对十字花科拟南芥中编码HMG CoA还原酶的基因之一HMG1的时空调控进行了表征。此外，HMG1启动子在不同器官中对光照有不同的反应，光剥夺引起的启动子激活主要局限于未成熟叶片。相比之下，HMG1基因在根中的表达局限于伸长区，且对光照无反应。光介导的HMG1表达调控被证明是一种依赖于直接光照的器官自主反应，拟南芥不同器官之间似乎不会交换有关光的环境信号。这些研究揭示了HMG1调控的几个新特征，并表明在未成熟叶片中检测到的高水平HMG CoA还原酶表达可能主要归因于HMG1的黑暗诱导表达，并且HMG1在整个植物中对光的反应下表达水平较低。因此，环境信号与发育程序相互作用，以确定拟南芥中HMG1基因的表达模式。
