Wyrich R, Dressen U, Brockmann S, Streubel M, Chang C, Qiang D, Paterson A H, Westhoff P
Institut für Entwicklungs- und Molekularbiologie der Pflanzen, Heinrich-Heine-Universität, Düsseldorf, Germany.
Plant Mol Biol. 1998 May;37(2):319-35. doi: 10.1023/a:1005900118292.
C4 photosynthesis depends upon the strict compartmentalization of the CO2-assimilatory enzymes of the C4 and Calvin cycle in two different cell types, mesophyll and bundle-sheath cells. A differential accumulation is also observed for enzymes of other metabolic pathways, and mesophyll and bundle-sheath chloroplasts of NADP-malic enzyme type C4 plants differ even in their photosynthetic electron transport chains. A large number of studies indicate that this division of labour between mesophyll and bundle-sheath cells is the result of differential gene expression. To investigate the extent of this differential gene expression and thus gain insight into the genetic basis of C4 photosynthesis, genes that are differentially expressed in the mesophyll and bundle-sheath cells were catalogued in the NADP-malic enzyme type C4 grass Sorghum bicolor. A total of 58 cDNAs were isolated by differential screening. Using a tenfold difference in transcript abundance between mesophyll and bundle-sheath cells as a criterion, 25 cDNAs were confirmed to encode mesophyll-specific gene sequences and 8 were found to encode bundle-sheath-specific sequences. Eight mesophyll-specific cDNAs showed no significant similarities within GenBank and may therefore represent candidates for the elucidation of hitherto unknown functions in the differentiation of mesophyll and bundle-sheath cells. The chromosomal location of 50 isolated cDNAs was determined by RFLP mapping using an interspecific sorghum cross.
C4光合作用依赖于C4途径和卡尔文循环中二氧化碳同化酶在叶肉细胞和维管束鞘细胞这两种不同细胞类型中的严格区室化。在其他代谢途径的酶中也观察到差异积累，并且NADP-苹果酸酶型C4植物的叶肉和维管束鞘叶绿体甚至在其光合电子传递链方面也有所不同。大量研究表明，叶肉细胞和维管束鞘细胞之间的这种分工是基因差异表达的结果。为了研究这种差异基因表达的程度，从而深入了解C4光合作用的遗传基础，对在NADP-苹果酸酶型C4禾本科植物双色高粱的叶肉细胞和维管束鞘细胞中差异表达的基因进行了编目。通过差异筛选总共分离出58个cDNA。以叶肉细胞和维管束鞘细胞中转录本丰度相差10倍为标准，确认25个cDNA编码叶肉特异性基因序列，8个被发现编码维管束鞘特异性序列。8个叶肉特异性cDNA在GenBank中未显示出明显的相似性，因此可能代表了阐明叶肉细胞和维管束鞘细胞分化中迄今未知功能的候选基因。使用种间高粱杂交通过RFLP图谱分析确定了50个分离的cDNA的染色体定位。
