Enjuto M, Lumbreras V, Marín C, Boronat A
Departament de Bioquímica i Fisiologia, Facultat de Química, Universitat de Barcelona, Spain.
Plant Cell. 1995 May;7(5):517-27. doi: 10.1105/tpc.7.5.517.
The synthesis of mevalonate, which is considered the first rate-limiting step in isoprenoid biosynthesis, is catalyzed by the enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR; EC 1.1.1.34). In Arabidopsis, HMGR is encoded by two differentially expressed genes (HMG1 and HMG2). The transcriptional activity of the HMG2 gene was studied after fusing different regions of its 5' flanking region to the beta-glucuronidase (GUS) reporter gene and transforming the resulting constructs into tobacco plants. The spatial and temporal expression directed by the HMG2 promoter in the transgenic plants is consistent with the expression pattern previously established by RNA analysis using an HMG2-specific probe. HMG2 expression is restricted to meristematic (root tip and shoot apex) and floral (secretory zone of the stigma, mature pollen grains, gynoecium vascular tissue, and fertilized ovules) tissues. Deletion analysis of the HMG2 5' flanking region was conducted in transgenic plants and transfected protoplasts. The region containing nucleotides -857 to +64 of the HMG2 gene was sufficient to confer high levels of expression in both floral and meristematic tissues, although deletion to nucleotide -503 resulted in almost complete loss of expression. Sequences contained within the 5' transcribed, untranslated region are also important for gene expression. The biological significance of the restricted pattern of expression of HMG2 is also discussed.
甲羟戊酸的合成被认为是类异戊二烯生物合成中的第一个限速步骤，该过程由3-羟基-3-甲基戊二酰辅酶A还原酶（HMGR；EC 1.1.1.34）催化。在拟南芥中，HMGR由两个差异表达的基因（HMG1和HMG2）编码。将HMG2基因5'侧翼区的不同区域与β-葡萄糖醛酸酶（GUS）报告基因融合，然后将所得构建体转化到烟草植株中，之后对HMG2基因的转录活性进行了研究。HMG2启动子在转基因植株中指导的时空表达与先前使用HMG2特异性探针通过RNA分析所确定的表达模式一致。HMG2的表达仅限于分生组织（根尖和茎尖）和花组织（柱头分泌区、成熟花粉粒、雌蕊维管组织和受精胚珠）。在转基因植株和转染的原生质体中对HMG2 5'侧翼区进行了缺失分析。HMG2基因中包含核苷酸-857至+64的区域足以在花组织和分生组织中均赋予高水平表达，尽管缺失至核苷酸-503会导致表达几乎完全丧失。5'转录非翻译区内包含的序列对基因表达也很重要。文中还讨论了HMG2表达受限模式的生物学意义。
