Expanded male sex-determining region conserved during the evolution of homothallism in the green alga Volvox

Kayoko Yamamoto; Ryo Matsuzaki; Wuttipong Mahakham; Wirawan Heman; Hiroyuki Sekimoto; Masanobu Kawachi; Yohei Minakuchi; Atsushi Toyoda; Hisayoshi Nozaki

doi:10.1016/j.isci.2023.106893

Expanded male sex-determining region conserved during the evolution of homothallism in the green alga Volvox

iScience. 2023 Jun 1;26(6):106893. doi: 10.1016/j.isci.2023.106893. eCollection 2023 Jun 16.

Authors

Kayoko Yamamoto¹, Ryo Matsuzaki², Wuttipong Mahakham³, Wirawan Heman⁴, Hiroyuki Sekimoto¹, Masanobu Kawachi², Yohei Minakuchi⁵, Atsushi Toyoda⁵, Hisayoshi Nozaki^{2

6}

Affiliations

¹ Department of Chemical and Biological Sciences, Faculty of Science, Japan Women's University, Tokyo 112-8681 Japan.
² Biodiversity Division, National Institute for Environmental Studies, Tsukuba 305-8506, Japan.
³ Department of Biology & Applied Taxonomic Research Center, Faculty of Science, Khon Kaen University, Khon Kaen, Thailand.
⁴ Department of Science and Mathematics, Faculty of Science and Health Technology, Kalasin University, Mueang Kalasin, Thailand.
⁵ Department of Genomics and Evolutionary Biology, National Institute of Genetics, Mishima 411-8540, Japan.
⁶ Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan.

Abstract

Male and female genotypes in heterothallic (self-incompatible) species of haploid organisms, such as algae and bryophytes, are generally determined by male and female sex-determining regions (SDRs) in the sex chromosomes. To resolve the molecular genetic basis for the evolution of homothallic (bisexual and self-compatible) species from a heterothallic ancestor, we compared whole-genome data from Thai and Japanese genotypes within the homothallic green alga Volvox africanus. The Thai and Japanese algae harbored expanded ancestral male and female SDRs of ∼1 Mbp each, representing a direct heterothallic ancestor. Therefore, the expanded male and female ancestral SDRs may originate from the ancient (∼75 mya) heterothallic ancestor, and either might have been conserved during the evolution of each homothallic genotype. An expanded SDR-like region seems essential for homothallic sexual reproduction in V. africanus, irrespective of male or female origin. Our study stimulates future studies to elucidate the biological significance of such expanded genomic regions.

Keywords: Chromosome organization; Phylogenetics; Plant evolution.