2002 Fiscal Year Final Research Report Summary
Comparative Studies for Deducing Functions of Chloroplast Structures in Green Plants
| Project/Area Number |
11440241
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
生物形態・構造
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| Research Institution | The University of Tokyo |
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Principal Investigator |
NOZAKI Hisayoshi Graduate School of Science, the Univerity of Tokyo, Associate Professor, 大学院・理学系研究科, 助教授 (40250104)
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| Co-Investigator(Kenkyū-buntansha) |
MIYAMURA Shinichi Institute of Biological Sciences, University of Tsukuba, Assistant Professor, 生物科学系, 講師 (00192766)
HORI Terumitsu Institute of Biological Sciences, University of Tsukuba, Professor Emeritus, 生物科学系, 名誉教授 (90057563)
KATO Masahiro Graduate School of Science, the Univerity of Tokyo, Professor, 大学院・理学系研究科, 教授 (20093221)
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| Project Period (FY) |
1999 – 2002
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| Keywords | Chloroplast / Molecular phylogenetic analysis / Morphological evolution / rbcL genes / Cellular function / Green plants / Ultrastructure / Pyrenoid |
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| Research Abstract |
The morphology of the pyrenoid and the physiology of the CO2-concentrating mechanism (CCM) were investigated in Chloromonas and related species of Chlamydomonas. Based on the results obtained, it was speculated that the presence of typical pyrenoids with a high concentration of Rubisco molecules is related to the formation of large Ci pools in the CCM. Detailed phylogenetic relationships among these Chlamydomonas/Chloromonas strains and the pyrenoid-less Chloromonas strains previously investigated were inferred based on the sequence of rbcL, the gene for the large subunit of Rubisco. Two monophyletic groups were resolved with high bootstrap values. Based on the tree topology resolved, it was inferred that loss of the typical pyrenoids accompanied by a decrease in intracellular Ci pools might have taken place independently in the two groups. This is the first demonstration of concrete function of the chloroplast structure pyrenoid.
We further compared sequences of the rbcL genes of pyrenoid-less Chloromonas species with those of closely related pyrenoid-containing Chlamydomonas species in the "Chloromonas lineage" and with those of 45 other green algae. We found that the proteins encoded by the rbcL genes had a much higher level of amino acid substitution in members of the Chloromonas lineage than they did in other algae. A phylogenetic tree based on rbcL nucleotide sequences nested two Chlamydomonas species as a "pyrenoid-regained" clade within a monophyletic Chloromonas "pyrenoid-lost" clade. However, both the atpB and the psaB sequence data gave robust support for a rather different set of phylogenetic relationships in which neither the "pyrenoid-lost" nor the "pyrenoid-regained" clade was resolved. The appearance of such clades in the rbcL-based tree may be an artifact of convergent evolutionary changes that have occurred in a region of the large subunit that determines whether Rubisco molecules will aggregate to form a visible pyrenoid.
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