Yamamoto Y Y, Kondo Y, Kato A, Tsuji H, Obokata J
Division of Bioscience, Graduate School of Environmental Earth Science, Hokkaido University, Sapporo, Japan.
Plant J. 1997 Aug;12(2):255-65. doi: 10.1046/j.1365-313x.1997.12020255.x.
psaDb is a nuclear gene encoding the ferredoxin-binding subunit of photosystem I in Nicotiana sylvestris. The organization of the light-responsive cis-elements of psaDb was studied using transgenic tobacco plants. Three types of psaDb chimeric constructs were created: (1) a 5' upstream fragment of psaDb transcriptionally fused with the beta-glucuronidase (GUS) gene, and a series of its 5' deletion derivatives, (2) the transcribed region of psaDb driven by the cauliflower mosaic virus (CaMV) 35S promoter, and (3) the 5' terminal 35 bases (the entire leader, +1 to +23, and the initiation codon context, +24 to +35) of the psaDb mRNA translationally fused with a GUS reporter gene under the operation of the CaMV 35S promoter. Light-responsiveness of these fusions in transgenic plants was examined by GUS assay and primer extension analysis. The results indicate that the light-responsive elements (LRE) of psaDb are located both upstream (-170 to +24) and within (+1 to +861) the transcribed region. The internal LRE is utilized in etiolated seedings but not in green leaves. The leader and initiation codon context construct (+1 to +35) did not show any light-response under the conditions tested. Therefore, it is likely that a combination of the upstream and internal LREs generates the complex light-responsive and tissue-specific regulation of this gene. This study also revealed that psaDb has adjacent activator (-267 to -254) and repressor (-253 to -234) regions for basal transcriptional activity; the former contains the ACGT binding motif recognized by many plant bZIP proteins, and the latter has the R3 decamer motif found in several photosystem I-related genes.
psaDb是一种核基因，编码野生烟草中光系统I的铁氧化还原蛋白结合亚基。利用转基因烟草植株研究了psaDb光响应顺式元件的组织情况。构建了三种类型的psaDb嵌合构建体：（1）psaDb的5'上游片段与β-葡萄糖醛酸酶（GUS）基因转录融合，以及一系列其5'缺失衍生物；（2）由花椰菜花叶病毒（CaMV）35S启动子驱动的psaDb转录区；（3）psaDb mRNA的5'末端35个碱基（整个前导序列，+1至+23，以及起始密码子上下文，+24至+35）与CaMV 35S启动子作用下的GUS报告基因翻译融合。通过GUS分析和引物延伸分析检测了这些融合体在转基因植物中的光响应性。结果表明，psaDb的光响应元件（LRE）位于转录区的上游（-170至+24）和内部（+1至+861）。内部LRE在黄化幼苗中起作用，但在绿叶中不起作用。前导序列和起始密码子上下文构建体（+1至+35）在测试条件下未显示任何光响应。因此，上游和内部LRE的组合可能产生该基因复杂的光响应和组织特异性调控。本研究还揭示，psaDb具有相邻的基础转录活性激活子（-267至-254）和抑制子（-253至-234）区域；前者包含许多植物bZIP蛋白识别的ACGT结合基序，后者具有在几个光系统I相关基因中发现的R3十聚体基序。
