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  • Three genomes in the algal genus Volvox reveal the fate of a haploid sex-determining region after a transition to homothallism
Title: Three genomes in the algal genus Volvox reveal the fate of a haploid sex-determining region after a transition to homothallism
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 female-determining 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.  more » « less
Award ID(s):
1755430
PAR ID:
10288145
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Proceedings of the National Academy of Sciences
Volume:
118
Issue:
21
ISSN:
0027-8424
Page Range / eLocation ID:
e2100712118
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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