Matsuoka M, Kyozuka J, Shimamoto K, Kano-Murakami Y
National Institute of Agrobiological Resources, Ibaraki, Japan.
Plant J. 1994 Sep;6(3):311-9. doi: 10.1046/j.1365-313x.1994.06030311.x.
C4 plants have two carboxylases which function in photosynthesis. One, phosphoenolpyruvate carboxylase (PEPC) is localized in mesophyll cells, and the other, ribulose bisphosphate carboxylase (RuBPC) is found in bundle sheath cells. In contrast, C3 plants have only one photosynthetic carboxylase, RuBPC, which is localized in mesophyll cells. The expression of PEPC in C3 mesophyll cells is quite low relative to PEPC expression in C4 mesophyll cells. Two chimeric genes have been constructed consisting of the structural gene encoding beta-glucuronidase (GUS) controlled by two promoters from C4 (maize) photosynthetic genes: (i) the PEPC gene (pepc) and (ii) the small subunit of RuBPC (rbcS). These constructs were introduced into a C3 cereal, rice. Both chimeric genes were expressed almost exclusively in mesophyll cells in the leaf blades and leaf sheaths at high levels, and no or very little activity was observed in other cells. The expression of both genes was also regulated by light. These observations indicate that the regulation systems which direct cell-specific and light-inducible expression of pepc and rbcS in C4 plants are also present in C3 plants. Nevertheless, expression of endogenous pepc in C3 plants is very low in C3 mesophyll cells, and the cell specificity of rbcS expression in C3 plants differs from that in C4 plants. Rice nuclear extracts were assayed for DNA-binding protein(s) which interact with a cis-regulatory element in the pepc promoter. Gel-retardation assays indicate that a nuclear protein with similar DNA-binding specificity to a maize nuclear protein is present in rice.(ABSTRACT TRUNCATED AT 250 WORDS)
C4植物有两种在光合作用中起作用的羧化酶。一种是磷酸烯醇式丙酮酸羧化酶（PEPC），位于叶肉细胞中；另一种是核酮糖二磷酸羧化酶（RuBPC），存在于维管束鞘细胞中。相比之下，C3植物只有一种光合羧化酶RuBPC，位于叶肉细胞中。相对于C4叶肉细胞中PEPC的表达，C3叶肉细胞中PEPC的表达相当低。已经构建了两个嵌合基因，它们由编码β-葡萄糖醛酸酶（GUS）的结构基因组成，该结构基因受来自C4（玉米）光合基因的两个启动子控制：（i）PEPC基因（pepc）和（ii）RuBPC的小亚基（rbcS）。将这些构建体导入一种C3谷类作物水稻中。这两个嵌合基因几乎只在叶片和叶鞘的叶肉细胞中高水平表达，在其他细胞中未观察到或观察到极少的活性。这两个基因的表达也受光调节。这些观察结果表明，在C4植物中指导pepc和rbcS细胞特异性和光诱导表达的调控系统在C3植物中也存在。然而，C3植物中内源性pepc在C3叶肉细胞中的表达非常低，并且C3植物中rbcS表达的细胞特异性与C4植物不同。对水稻核提取物进行了与pepc启动子中的顺式调控元件相互作用的DNA结合蛋白检测。凝胶阻滞试验表明，水稻中存在一种与玉米核蛋白具有相似DNA结合特异性的核蛋白。（摘要截短于250字）
