Suzuki J Y, Bauer C E
Department of Biology, Indiana University, Bloomington 47405.
Plant Cell. 1992 Aug;4(8):929-40. doi: 10.1105/tpc.4.8.929.
The Chlamydomonas reinhardtii chloroplast gene chlL (frxC) is shown to be involved in the light-independent conversion of protochlorophyllide to chlorophyllide. The polypeptide encoded by chlL contains a striking 53% amino acid sequence identity with the bacteriochlorophyll (bch) biosynthesis bchL gene product in the photosynthetic bacterium Rhodobacter capsulatus. In a previous analysis, we demonstrated that bchL was involved in light-independent protochlorophyllide reduction, thereby implicating chlL in light-independent protochlorophyllide reduction in photosynthetic eukaryotes. To perform a functional/mutational analysis of chlL, we utilized particle gun-mediated transformation to disrupt the structural sequence of chlL at its endogenous locus in the chloroplast genome of Chlamydomonas. Transformants for which the multicopy chloroplast genome was homoplasmic for the disrupted chlL allele exhibit a "yellow-in-the-dark" phenotype that we demonstrated to be a result of the dark accumulation of protochlorophyllide. The presence of a chlL homolog in distantly related bacteria and nonflowering land plants, which are thought to be capable of synthesizing chlorophyll in the dark, was also demonstrated by cross-hybridization analysis. In contrast, we observed no cross-hybridization of a probe of chlL to DNA samples from representative angiosperms that require light for chlorophyll synthesis, in support of our conclusion that chlL is involved in light-independent chlorophyll biosynthesis. The role of chlL in protochlorophyllide reduction as well as recent evidence that both light-independent and light-dependent protochlorophyllide reductases may be of bacterial origin are discussed.
莱茵衣藻叶绿体基因chlL（frxC）被证明参与原叶绿素酸酯向叶绿素酸酯的非光依赖型转化。chlL编码的多肽与光合细菌荚膜红细菌中细菌叶绿素（bch）生物合成的bchL基因产物有着惊人的53%的氨基酸序列同一性。在先前的分析中，我们证明bchL参与非光依赖型原叶绿素酸酯还原，从而表明chlL在光合真核生物的非光依赖型原叶绿素酸酯还原中起作用。为了对chlL进行功能/突变分析，我们利用粒子枪介导的转化来破坏莱茵衣藻叶绿体基因组中chlL在其内源位点的结构序列。多拷贝叶绿体基因组对破坏的chlL等位基因呈同质性的转化体表现出“暗黄”表型，我们证明这是原叶绿素酸酯在黑暗中积累的结果。通过杂交分析还证明，在远缘相关细菌和非开花陆地植物中存在chlL同源物，这些植物被认为能够在黑暗中合成叶绿素。相反，我们观察到chlL探针与来自需要光进行叶绿素合成的代表性被子植物的DNA样品没有杂交，这支持了我们关于chlL参与非光依赖型叶绿素生物合成的结论。本文讨论了chlL在原叶绿素酸酯还原中的作用，以及最近关于非光依赖型和光依赖型原叶绿素酸酯还原酶可能都起源于细菌的证据。
