Comparative genomic studies on the evolution of cyanobacteria and plastids

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The aim of this study is to analyze the evolution of cyanobacterial endosymbiont to plastids using comparative genomic data based on prokaryotic and eukaryotic organisms. We identified some key components of the genomic machinery of plastids, and performed functional analysis of the components. Major results were the followings :1.We developed a new version (3.5) of the GCLUST software, which clusters predicted proteins of prokaryotic and eukaryotic organisms. This increased performance of clustering of large-scale genomic data.2.The 40 cyanobacterial genes that are included in the 37 clusters of functionally unknown genes, which are conserved in photosynthetic organisms, were disrupted. Fluorescence induction kinetic analysis indicated that many of them were affected in photosystems. Most of the Arabidopsis genes in the 37 gene clusters were light-induced, and the protein product of these genes were targeted to plastids. In addition, tag-lines that are disrupted in the genes in 20 of the clusters were analyzed. Three lines that showed visible phenotypes were found. There results demonstrate that the computationally extracted 37 gene clusters encode, in fact, plastid proteins of endosymbiont origin, which are novel factors involved in photosynthesis.3.Two DNA polymerases that are localized in the organelles of the unicellular red alga, Cyanidioschyzon merolae.4.Sulfite reductases in cyanobacteria, red alga, and green plants were analyzed with respect to DNA-binding activity and intracellular localization.5.A new technique was developed to visualize plastid nucleoids within live plant materials. Dynamism of plastid nucleoids in non-photosynthetic cells is now clearly demonstrated. During the division of plastid, nucleoids formed a network structure, which permitted even partition of nucleoids to daughter plastids.