Shiina T, Nishii A, Toyoshima Y, Bogorad L
Graduate School of Human and Environmental Studies, Kyoto University, Japan.
Plant Physiol. 1997 Oct;115(2):477-83. doi: 10.1104/pp.115.2.477.
Changes in cytoplasmic Ca2+ levels are involved in the regulation of several plant genes. However, to our knowledge, no regions of genes or specific cis elements have been shown to be involved in the regulation of plant gene expression by cytosolic Ca2+ signaling. The maize (Zea mays) gene cab-m1, which encodes a light-harvesting chlorophyll a/b-binding apoprotein, is positively photoregulated in mesophyll cells (MC) but not in bundle-sheath cells (BSC). This gene is highly preferentially expressed in maize MC versus BSC. In situ transient expression assays have revealed that exposure of tissues to ethyleneglycol-bis(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA), which chelates Ca2+, blocks the photostimulation of cab-m1 full promoter (-1026 to + 14) activity in MC of leaf segments of dark-grown maize seedlings. EGTA has no effect on expression in BSC. These results suggest that light-induced elevation of the cytosolic Ca2+ concentration in MC is required for the enhancement of cab-m1 expression in MC. Deletion of the sequence from -1026 to -360 completely abolished Ca2+ responsiveness of cab-m1 expression in MC. On the other hand, a 54-bp fragment in the 5' flanking region (-953 to -899 relative to the translation start site) conferred Ca2+ responsiveness on a -359 core promoter: reporter gene, suggesting that Ca2+ signaling is mediated via specific sequences in this short fragment. Furthermore, possible involvement of Ca(2+)-calmodulin in the signal transduction chain for regulating cab-m1 expression was suggested by the results of inhibitor experiments.
细胞质Ca2+水平的变化参与了多种植物基因的调控。然而，据我们所知，尚未发现基因的任何区域或特定的顺式元件参与胞质Ca2+信号对植物基因表达的调控。玉米（Zea mays）基因cab - m1编码一种捕光叶绿素a/b结合载脂蛋白，在叶肉细胞（MC）中受到正向光调节，但在维管束鞘细胞（BSC）中则不然。该基因在玉米叶肉细胞与维管束鞘细胞中高度优先表达。原位瞬时表达分析表明，将组织暴露于螯合Ca2+的乙二醇双（β - 氨基乙醚）- N，N'-四乙酸（EGTA）中，会阻断黑暗生长的玉米幼苗叶片切段叶肉细胞中cab - m1全启动子（-1026至 + 14）活性的光刺激。EGTA对维管束鞘细胞中的表达没有影响。这些结果表明，叶肉细胞中光诱导的胞质Ca2+浓度升高是叶肉细胞中cab - m1表达增强所必需的。从 - 1026至 - 360的序列缺失完全消除了叶肉细胞中cab - m1表达的Ca2+反应性。另一方面，5'侧翼区域（相对于翻译起始位点为 - 953至 - 899）中的一个54 bp片段赋予了 - 359核心启动子 - 报告基因Ca2+反应性，表明Ca2+信号是通过该短片段中的特定序列介导的。此外，抑制剂实验结果表明Ca(2+)-钙调蛋白可能参与了调节cab - m1表达的信号转导链。
