Analysis and modulation of photosynthetic metabolism through the mutagenesis of ferredoxin

以光合作用细胞中的电子载体蛋白铁氧还蛋白（ferredoxin，Fd）的结构、功能和基因表达为研究对象，探讨了光合作用细胞中电子分配到几种代谢途径的机制。本研究获得了以下结果：1）从玉米根中克隆了硝酸盐诱导Fd同工酶（FdVI）的cDNA和基因，发现其基因表达受硝酸盐同化酶的调控; 2）Fd同工酶FdI和FdII分别分布于叶肉细胞和维管束鞘细胞中，并在转录水平上观察到细胞特异性表达。将FdI和FdII基因转化到Fd缺陷型蓝藻中，以补充光合生长，两种Fds对C和N同化表现出不同的活性。3）对重组Fds的功能研究，确定了与[Fe-2S]簇氧化还原特性相关的氨基酸残基以及与Fd依赖酶的相互作用位点。4）克隆了谷氨酸合成酶基因Fd-GOGAT和NADH-GOGAT，并分离了基因缺失突变体，研究了这两种酶的体内功能。Fd-GOGAT被认为是负责N同化的同工酶，在音乐会与充足的光照条件下提高CO2固定。

The mechanisms of electron partitioning to several metabolic pathways in photosynthetic cells were studied in focusing structure, function, and gene expression of an electron carrier protein, ferredoxin (Fd). Following results have been obtained in this study.1) cDNA and gene for a nitrate inducible Fd isoprotein (FdVI) were cloned from maize roots, and its gene expression was found to be regulated with a manner similar to the nitrate assimilatory enzymes.2) Two different Fd isoproteins, FdI and FdII,were distributed in the mesophyll cells and the bundle sheath cells, respectively, and the cell specific expressions were observed in the transcriptional level. Genes to FdI and FdII were transformed a Fd-deficient cyanobacterium to complement the photosynthetic growth, and the two Fds showed a different activity to C and N assimilations.3) Study on the functions of recombinant Fds identified amino acid residues involved in the redox properties of the [Fe-2S] cluster and interaction sites to Fd-dependent enzymes. These mutant Fds will be used for modulate the photosynthetic ability of transgenic plants.4) Genes encoding two glutamate synthase, Fd-GOGAT and NADH-GOGAT,have been cloned, and the gene-disrupted mutants were isolated to study in vivo function of the enzymes. Fd-GOGAT was found to be the isozyme responsible to N assimilation in concert with an elevated CO2 fixation under sufficient light condition.