Functional Analysis of Isozymes of Light-dependent Protochlorophyllide Oxidoreductase on Chloroplast Biogenesis

原叶绿素(Pchlide)的还原是光养生物中叶绿素生物合成的关键调控步骤。在被子植物中，POR基因家族存在差异表达，POR亚型的基因表达受光照和发育的差异调控。为了阐明POR亚型(porA、PORB和porc)在拟南芥中的生理功能，我们分析了porB和porc的零突变。在强光和中光条件下，黄化PorB苗木的绿色度与野生型相当，而在弱光条件下绿色度显著降低。在绿化过程中，强光照射提高了PORC蛋白的水平，而强光抑制了PORC的绿化。这些结果表明，PORB除了PORA外，还对原生生物组装和光活性Pchlide的形成具有重要作用。很可能，在绿化之初，公共小巴就是进口…在不同的光照条件下，更多的蚂蚁能有效地捕捉光能进行光转化，而强光照射诱导的PORC有助于光保护作用，同时细胞分裂素和光激活了黄瓜POR基因的转录。为了确定与叶绿素生物合成和叶绿体发育相对应的细胞分裂素响应顺式元件，我们在黄化黄瓜子叶中进行了瞬时表达分析。A5‘-缺失分析表明，启动子区域至少含有一个与细胞分裂素反应相关的顺式元件。凝胶迁移率改变分析也检测到该区域细胞分裂素增强的结合。更详细的凝胶迁移率漂移和竞争分析确定5‘-TATTAG-3’是细胞分裂素增强结合的关键序列。瞬时表达试验中识别序列的突变导致细胞分裂素反应性降低，但仍保留，以及未处理对照的低报告活性。这些结果表明，所鉴定的序列是一个新的顺式元件，在体外显示出细胞分裂素依赖的蛋白结合，当与其他细胞分裂素相关元件相互作用时可能有效地发挥作用。较少

The reduction of protochlorophyllide (Pchlide) is a key regulatory step in the biosynthesis of chlorophyll in phototrophic organisms. In angiosperms, POR gene family is differentially represented, and gene expression of POR isoform is differentially regulated by light and development.To elucidate the physiological function of three differentially regulated POR isoforms (PORA, PORB and PORC) in Arabidopsis thaliana, we analyzed null mutants of porB and porC. When illuminated, etiolated porB seedling was able to green to the similar extent to the wild type under high and medium light conditions, while the greening was significantly reduced under low light condition. During greening, the high light irradiation increased the level of PORC protein, and the greening of porC was repressed under the high light condition. These results suggest that as well as PORA, PORB is also function for PLBs assembly and photoactive Pchlide formation. It is likely that, at onset of greening, PLBs are import … More ant for efficient capturing of light energy for photoconversion under various light conditions, and PORC, which is induced by high light irradiation, contributes to photoprotection.Meanwhile, cytokinins and light activate the transcription of the cucumber POR gene. To identify the cytokinin-responsive cis-element corresponding to chlorophyll biosynthesis and chloroplast development, we performed transient expression assays in etiolated cucumber cotyledons. A5'-deletional analysis indicated that the promoter region contained at least one of the cis-elements related to cytokinin-responsiveness. Gel mobility shift assays also detected cytokinin-enhanced binding in this region. More detailed gel mobility shift and competition analyzes identified 5'-TATTAG-3' as the sequence critical for cytokinin-enhanced binding. Mutations in the identified sequence in the transient expression assay caused a reduced but retained cytokinin-responsiveness, as well as low reporter activity of untreated control. These results suggest that the identified sequence is a novel cis-element exhibiting cytokinin-dependent protein binding in vitro, which may function effectively when interacting with other cytokinin-related elements. Less