Analysis and modulation of photosynthetic metabolism through the mutagenesis of ferredoxin

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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.