A prokaryotic origin for light-dependent chlorophyll biosynthesis of plants.
A prokaryotic origin for light-dependent chlorophyll biosynthesis of plants.
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植物光依赖性叶绿素生物合成的原核起源。
DOI：
10.1073/pnas.92.9.3749
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发表时间：
1995
影响因子：
11.1
通讯作者：
Bauer,CE
中科院分区：
文献类型：
--
作者：
Suzuki,JY;Bauer,CE
开花植物需要光来合成叶绿素。早期的研究表明，绿化对光的依赖部分源于叶绿素中间体原叶绿素在光的依赖下还原为产物叶绿素。开花植物对原叶绿素的光依赖性还原与非开花植物、藻类和光合细菌还原原叶绿素从而在黑暗中合成(细菌)叶绿素的能力形成对比。在这篇报道中，我们用蓝藻合胞杆菌基因组DNA组成的表达文库，在功能上补充了胶囊红细菌的光不依赖的原叶绿素还原酶突变体。PCC 6803。补充菌能够在光照下合成细菌叶绿素，表明叶绿素生物合成酶在细菌叶绿素生物合成途径中发挥作用。然而，在黑暗生长条件下，补充菌不能合成细菌叶绿素，而是积累了原叶绿素。序列分析表明，互补的聚球藻基因组DNA片段与植物中发现的依赖光的原叶绿素还原酶具有高度的序列同源性(53-56%)。蓝藻中存在一种植物类型的、依赖于光的原叶绿素还原酶，这表明依赖光的原叶绿素还原酶在真核光合作用出现之前就已经进化了。因此，这种酶的产生并不是为了履行叶绿体内共生进化所必需的功能，也不是为了履行多细胞进化所必需的功能；相反，它的进化是为了履行基本的细胞自主作用。
Flowering plants require light for chlorophyll synthesis. Early studies indicated that the dependence on light for greening stemmed in part from the light-dependent reduction of the chlorophyll intermediate protochlorophyllide to the product chlorophyllide. Light-dependent reduction of protochlorophyllide by flowering plants is contrasted by the ability of nonflowering plants, algae, and photosynthetic bacteria to reduce protochlorophyllide and, hence, synthesize (bacterio) chlorophyll in the dark. In this report, we functionally complemented a light-independent protochlorophyllide reductase mutant of the eubacterium Rhodobacter capsulatus with an expression library composed of genomic DNA from the cyanobacterium Synechocystis sp. PCC 6803. The complemented R. capsulatus strain is capable of synthesizing bacteriochlorophyll in the light, thereby indicating that a chlorophyll biosynthesis enzyme can function in the bacteriochlorophyll biosynthetic pathway. However, under dark growth conditions the complemented R. capsulatus strain fails to synthesize bacteriochlorophyll and instead accumulates protochlorophyllide. Sequence analysis demonstrates that the complementing Synechocystis genomic DNA fragment exhibits a high degree of sequence identity (53-56%) with light-dependent protochlorophyllide reductase enzymes found in plants. The observation that a plant-type, light-dependent protochlorophyllide reductase enzyme exists in a cyanobacterium indicates that light-dependent protochlorophyllide reductase evolved before the advent of eukaryotic photosynthesis. As such, this enzyme did not arise to fulfill a function necessitated either by the endosymbiotic evolution of the chloroplast or by multicellularity; rather, it evolved to fulfill a fundamentally cell-autonomous role.