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| サンゴに共生し、光合成産物を供給する褐虫藻 |
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| 褐虫藻の持つ遺伝子の進化 |
当研究室と沖縄科学技術大学院大学（OIST）の佐藤矩行教授の研究室との共同研究成果が、研究論文として科学誌PLoS Oneに受理されました。
総説のタイトルおよび要約は下記の通りです。
-Title-
Diversification of light harvesting complex gene family via intra- and intergenic duplications in the coral symbiotic alga Symbiodinium
-Authors-
Shinichiro Maruyama, Eiichi Shoguchi, Nori Satoh, and Jun Minagawa.
-Summary-
The light-harvesting complex (LHC) is an essential component in light energy capture and transduction to facilitate downstream photosynthetic reactions in plant and algal chloroplasts. The unicellular dinoflagellate alga Symbiodinium is an endosymbiont of cnidarian animals, including corals and sea anemones, and provides carbohydrates generated through photosynthesis to host animals. Although Symbiodinium possesses a unique LHC gene family, called chlorophyll a-chlorophyll c2-peridinin protein complex (acpPC), its genome-level diversity and evolutionary trajectories have not been investigated. Here, we describe a phylogenetic analysis revealing that many of the LHCs are encoded by highly duplicated genes with multi-subunit polyprotein structures in the nuclear genome of Symbiodinium minutum. This analysis provides an extended list of the LHC gene family in a single organism, including 80 loci encoding polyproteins composed of 145 LHC subunits recovered in the phylogenetic tree. In S. minutum, 5 phylogenetic groups of the Lhcf-type gene family, which is exclusively conserved in algae harboring secondary plastids of red algal origin, were identified. Moreover, 5 groups of the Lhcr-type gene family, of which members are known to be associated with PSI in red algal plastids and secondary plastids of red algal origin, were identified. Notably, members classified within a phylogenetic group of the Lhcf-type (group F1) are highly duplicated, which may explain the presence of an unusually large number of LHC genes in this species. Some gene units were homologous to other units within single loci of the polyprotein genes, whereas intergenic homologies between separate loci were conspicuous in other cases, implying that gene unit ‘shuffling’ by gene conversion and/or genome rearrangement might have been a driving force for diversification. These results suggest that vigorous intra- and intergenic gene duplication events have resulted in the genomic framework of photosynthesis in coral symbiont dinoflagellate algae.
オンライン論文はコチラ
-簡単な解説-
サンゴなど刺胞動物の共生藻として知られる褐虫藻Symbiodinium（渦鞭毛藻の一種）は光合成により光エネルギーを糖などに変えて宿主に供給しています。褐虫藻のゲノムには光合成において重要な役割と果たす光受容アンテナ複合体の遺伝子が数多く存在することが知られていますが、どのようにしてそれらの膨大な数の遺伝子が進化してきたのかは分かっていませんでした。
今回の研究では、褐虫藻の持つ光受容アンテナ複合体遺伝子を全ゲノム規模で分子系統学的に解析することにより、ある特定の遺伝子ファミリーで爆発的に遺伝子数が増加していること、遺伝子数の増大は「遺伝子間重複」と「遺伝子内重複」という過程を繰り返して生じてきたこと、また生物史的にはこうした遺伝子重複は褐虫藻が種分化する以前に起きていたことが示されました。今回の成果により、褐虫藻がサンゴなどとの共生関係を営む上で、実際にどのように光合成機能を維持しているのかを研究する上での重要な足がかりが得られました。
The light-harvesting complex (LHC) is an essential component in light energy capture and transduction to facilitate downstream photosynthetic reactions in plant and algal chloroplasts. The unicellular dinoflagellate alga Symbiodinium is an endosymbiont of cnidarian animals, including corals and sea anemones, and provides carbohydrates generated through photosynthesis to host animals. Although Symbiodinium possesses a unique LHC gene family, called chlorophyll a-chlorophyll c2-peridinin protein complex (acpPC), its genome-level diversity and evolutionary trajectories have not been investigated. Here, we describe a phylogenetic analysis revealing that many of the LHCs are encoded by highly duplicated genes with multi-subunit polyprotein structures in the nuclear genome of Symbiodinium minutum. This analysis provides an extended list of the LHC gene family in a single organism, including 80 loci encoding polyproteins composed of 145 LHC subunits recovered in the phylogenetic tree. In S. minutum, 5 phylogenetic groups of the Lhcf-type gene family, which is exclusively conserved in algae harboring secondary plastids of red algal origin, were identified. Moreover, 5 groups of the Lhcr-type gene family, of which members are known to be associated with PSI in red algal plastids and secondary plastids of red algal origin, were identified. Notably, members classified within a phylogenetic group of the Lhcf-type (group F1) are highly duplicated, which may explain the presence of an unusually large number of LHC genes in this species. Some gene units were homologous to other units within single loci of the polyprotein genes, whereas intergenic homologies between separate loci were conspicuous in other cases, implying that gene unit ‘shuffling’ by gene conversion and/or genome rearrangement might have been a driving force for diversification. These results suggest that vigorous intra- and intergenic gene duplication events have resulted in the genomic framework of photosynthesis in coral symbiont dinoflagellate algae.
オンライン論文はコチラ
-簡単な解説-
サンゴなど刺胞動物の共生藻として知られる褐虫藻Symbiodinium（渦鞭毛藻の一種）は光合成により光エネルギーを糖などに変えて宿主に供給しています。褐虫藻のゲノムには光合成において重要な役割と果たす光受容アンテナ複合体の遺伝子が数多く存在することが知られていますが、どのようにしてそれらの膨大な数の遺伝子が進化してきたのかは分かっていませんでした。
今回の研究では、褐虫藻の持つ光受容アンテナ複合体遺伝子を全ゲノム規模で分子系統学的に解析することにより、ある特定の遺伝子ファミリーで爆発的に遺伝子数が増加していること、遺伝子数の増大は「遺伝子間重複」と「遺伝子内重複」という過程を繰り返して生じてきたこと、また生物史的にはこうした遺伝子重複は褐虫藻が種分化する以前に起きていたことが示されました。今回の成果により、褐虫藻がサンゴなどとの共生関係を営む上で、実際にどのように光合成機能を維持しているのかを研究する上での重要な足がかりが得られました。
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