Chye M L, Tan C T, Chua N H
Institute of Molecular and Cell Biology, National University of Singapore, Republic of Singapore.
Plant Mol Biol. 1992 Jun;19(3):473-84. doi: 10.1007/BF00023395.
The enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) catalyses an important step in isoprenoid biosynthesis in plants. In Hevea brasiliensis, HMGR is encoded by a small gene family comprised of three members, hmg1, hmg2 and hmg3. We have previously described hmg1 and hmg2 (Plant Mol Biol 16: 567-577, 1991). Here we report the isolation and characterization of hmg3 genomic and cDNA clones. In comparison to hmg1 which is more highly expressed in laticifers than in leaves, the level of hmg3 mRNA level is equally abundant in laticifers and leaves. In situ hybridization experiments showed that the expression of hmg3 is not cell-type specific while hmg1 is expressed predominantly in the laticifers. Primer-extension experiments using laticifer RNA showed that hmg1 is induced by ethylene while hmg3 expression remains constitutive. The hmg3 promoter, like the promoters of most housekeeping genes, lacks a TATA box. Our results suggest that hmg1 is likely to encode the enzyme involved in rubber biosynthesis while hmg3 is possibly involved in isoprenoid biosynthesis of a housekeeping nature.
3-羟基-3-甲基戊二酰辅酶A还原酶（HMGR）催化植物类异戊二烯生物合成中的一个重要步骤。在巴西橡胶树中，HMGR由一个由三个成员hmg1、hmg2和hmg3组成的小基因家族编码。我们之前已经描述了hmg1和hmg2（《植物分子生物学》16: 567 - 577, 1991）。在此我们报告hmg3基因组和cDNA克隆的分离与特性分析。与在乳汁管中比在叶片中表达更高的hmg1相比，hmg3 mRNA在乳汁管和叶片中的丰度相当。原位杂交实验表明hmg3的表达不是细胞类型特异性的，而hmg1主要在乳汁管中表达。使用乳汁管RNA进行的引物延伸实验表明hmg1受乙烯诱导，而hmg3的表达保持组成型。hmg3启动子与大多数持家基因的启动子一样，缺乏TATA框。我们的结果表明hmg1可能编码参与橡胶生物合成的酶，而hmg3可能参与维持细胞基本功能的类异戊二烯生物合成。
