Maruyama Shinichiro, Shoguchi Eiichi, Satoh Nori, Minagawa Jun
Division of Environmental Photobiology, National Institute for Basic Biology, Okazaki, Aichi, Japan.
Marine Genomics Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa, Japan.
PLoS One. 2015 Mar 5;10(3):e0119406. doi: 10.1371/journal.pone.0119406. eCollection 2015.
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.
捕光复合体（LHC）是植物和藻类叶绿体中捕获光能并将其转化以促进下游光合作用反应的重要组成部分。单细胞甲藻共生藻是包括珊瑚和海葵在内的刺胞动物的内共生体，通过光合作用产生碳水化合物并提供给宿主动物。尽管共生藻拥有一个独特的LHC基因家族，即叶绿素a - 叶绿素c2 - 多甲藻素蛋白复合体（acpPC），但其基因组水平的多样性和进化轨迹尚未得到研究。在此，我们描述了一项系统发育分析，该分析揭示了许多LHC由微小共生藻核基因组中具有多亚基多聚蛋白结构的高度重复基因编码。该分析提供了单个生物体中LHC基因家族的扩展列表，包括在系统发育树中恢复的80个编码由145个LHC亚基组成的多聚蛋白的基因座。在微小共生藻中，鉴定出了Lhcf型基因家族的5个系统发育组，该家族仅在具有红藻起源的次生质体的藻类中保守。此外，还鉴定出了Lhcr型基因家族的5个组，已知其成员与红藻质体和红藻起源的次生质体中的PSI相关。值得注意的是，归类在Lhcf型（F1组）系统发育组内的成员高度重复，这可能解释了该物种中存在异常大量的LHC基因。一些基因单元与多聚蛋白基因单个基因座内的其他单元同源，而在其他情况下，不同基因座之间的基因间同源性很明显，这意味着通过基因转换和/或基因组重排进行的基因单元“洗牌”可能是多样化的驱动力。这些结果表明，活跃的基因内和基因间重复事件导致了珊瑚共生甲藻光合作用的基因组框架。
