期刊
出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.2100712118
关键词
evolution; sex; Volvox; heterothallism; homothallism
资金
- Japan Society for the Promotion of Science (JSPS) [18J11391]
- NSF [IOS 1755430]
- Ministry of Education, Culture, Sports, Science and Technology (MEXT) /JSPS KAKENHI [16H06279, 16H02518, 20H03299, 17K07510, 17H05840]
Transitions between separate sexes and other mating systems are common in eukaryotes, with the research on a haploid dioecious green algal species showing a breakdown of dioecy. The investigation into the sex-determining gene regions in different species revealed variations in the SDR and the involvement of homothallism in the breakdown of dioecy.
Transitions between separate sexes (dioecy) and other mating systems are common across eukaryotes. Here, we study a change in a haploid dioecious green algal species with male- and femaledetermining chromosomes (U and V). The genus Volvox is an oogamous (with large, immotile female gametes and small, motile male gametes) and includes both heterothallic species (with distinct male and female genotypes, associated with a mating-type system that prevents fusion of gametes of the same sex) and homothallic species (bisexual, with the ability to self-fertilize). We date the origin of an expanded sex-determining region (SDR) in Volvox to at least 75 Mya, suggesting that homothallism represents a breakdown of dioecy (heterothallism). We investigated the involvement of the SDR of the U and V chromosomes in this transition. Using de novo whole-genome sequences, we identified a heteromorphic SDR of ca 1 Mbp in male and female genotypes of the heterothallic species Volvox reticuliferus and a homologous region (SDLR) in the closely related homothallic species Volvox africanus, which retained several different hallmark features of an SDR. The V. africanus SDLR includes a large region resembling the female SDR of the presumptive heterothallic ancestor, whereas most genes from the male SDR are absent. However, we found a multicopy array of the male-determining gene, MID, in a different genomic location from the SDLR. Thus, in V. africanus, an ancestrally female genotype may have acquired MID and thereby gained male traits.
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