Anisogamy evolved with a reduced sex-determining region in volvocine green algae
Takashi Hamaji, Hiroko Kawai-Toyooka, Haruka Uchimura, Masahiro Suzuki, Hideki Noguchi, Yohei Minakuchi, Atsushi Toyoda, Asao Fujiyama, Shin-ya Miyagishima, James G. Umen & Hisayoshi Nozaki
Communications Biology volume 1, Article number: 17 (2018)
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Comparative genomics Evolutionary biology Evolutionary genetics
Received: 16 November 2017 Accepted: 08 February 2018
Published online: 08 March 2018
Abstract
Male and female gametes differing in size—anisogamy—emerged independently from isogamous ancestors in various eukaryotic lineages, although genetic bases of this emergence are still unknown. Volvocine green algae are a model lineage for investigating the transition from isogamy to anisogamy. Here we focus on two closely related volvocine genera that bracket this transition—isogamous Yamagishiella and anisogamous Eudorina. We generated de novo nuclear genome assemblies of both sexes of Yamagishiella and Eudorina to identify the dimorphic sex-determining chromosomal region or mating-type locus (MT) from each. In contrast to the large (>1 Mb) and complex MT of oogamous Volvox, Yamagishiella and Eudorina MT are smaller (7–268 kb) and simpler with only two sex-limited genes—the minus/male-limited MID and the plus/female-limited FUS1. No prominently dimorphic gametologs were identified in either species. Thus, the first step to anisogamy in volvocine algae presumably occurred without an increase in MT size and complexity.
Acknowledgements
We thank the staff of Comparative Genomics Laboratory at NIG for supporting genome sequencing. Computations were partially performed on the NIG supercomputer at ROIS National Institute of Genetics. This work was supported by a Grants-in-Aid for Scientific Research on Innovative Areas “Genome Science” (grant number 221S0002; to A.T. and A.F.), Scientific Research (A) (grant number 16H02518; to H.Nozaki), Research Activity Startup grants (grant number 16H06734 to T.H.), Scientific Research (C) (grant number 17K07510 to H.K.-T.), Grant-in-Aid for Scientific Research on Innovative Areas (grant number 17H05840 to T.H.) from MEXT/JSPS KAKENHI, and National Institutes of Health (grant number GM 078376 to J.G.U.).
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Author notes
Takashi Hamaji
Present address: Department of Biological Sciences, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto, 606-8502, Japan
These authors contributed equally: Takashi Hamaji, Hiroko Kawai-Toyooka.
Affiliations
Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan
Takashi Hamaji, Hiroko Kawai-Toyooka, Haruka Uchimura & Hisayoshi Nozaki
Kobe University Research Center for Inland Seas, Awaji, Hyogo, 656-2401, Japan
Masahiro Suzuki
Center for Genome Informatics, Joint Support-Center for Data Science Research, Research Organization of Information and Systems, Mishima, Shizuoka, 411-8540, Japan
Hideki Noguchi
Advanced Genomics Center, National Institute of Genetics, Mishima, Shizuoka, 411-8540, Japan
Hideki Noguchi, Atsushi Toyoda & Asao Fujiyama
Center for Information Biology, National Institute of Genetics, Mishima, Shizuoka, 411-8540, Japan
Yohei Minakuchi & Atsushi Toyoda
Department of Cell Genetics, National Institute of Genetics, Mishima, Shizuoka, 411-8540, Japan
Shin-ya Miyagishima
Donald Danforth Plant Science Center, 975 N Warson Rd, St. Louis, MO, 63132, USA
James G. Umen
Contributions
Conceived the study: H.Nozaki. Designed the study: T.H., H.K.-T., H.Nozaki. Prepared genomic DNA: M.S. Performed whole-genome sequencing and assembly: H.Noguchi., Y.M. A.T., A.F. Performed the experiments: T.H., H.K.-T., H.U. Analyzed the data: T.H., H.K.-T., H.Nozaki. Contributed materials: S.-y.M. Wrote and edited the manuscript: T.H., H.K.-T., A.T., J.G.U., H.Nozaki.
Competing interests
The authors declare no competing interests.
Corresponding authors
Correspondence to Hiroko Kawai-Toyooka or Hisayoshi Nozaki.
