Multiple convergent events of recombination suppression in mating-type chromosomes

Tatiana Giraud
Laboratory of Ecology, Systematics and Evolution, Université Paris Sud, France

tatiana.giraud (at) u-psud.fr

Convergent adaptation provides unique insights into the predictability of evolution and ultimately into processes of biological diversification. Supergenes (beneficial gene linkage) are striking examples of adaptation. We show that anther-smut fungi evolved supergene formation by rearrangements linking two key mating-type loci, thus increasing the odds of gamete compatibility under selfing. High-quality genome assemblies revealed six independent cases of chromosomal rearrangements leading to regions of suppressed recombination linking these mating-type loci in closely related species. Such convergent transitions in genomic architecture of mating-type determination indicate strong selection favoring linkage of mating-type loci into cosegregating supergenes. We further found independent evolutionary strata (stepwise extension of recombination suppression) in several species, despite the lack of sexual antagonism in these isogamous fungi. Sexual antagonism is the most commonly accepted evolutionary theory for the existence of stepwise extension of recombination suppression in sex chromosomes, but our findings show that other mechanisms can generate evolutionary strata.

Recent publications:

1 Branco  S, Badouin H, Rodriguez de la Vega R, Gouzy J, Carpentier F, Aguileta G, Siguenza S, Brandenburg JT, Coelho M, Hood ME, Giraud T (2017) Evolutionary strata on young mating-type chromosomes despite lack of sexual antagonism PNAS. 114: 7067–7072.

2 Branco   S, Carpentier F, Rodriguez de la Vega R, Badouin H, Snirc A, Le Prieur S, Coelho M, de Vienne D.M., Hartmann F, Begerow D, Hood ME, Giraud T (2018) Multiple convergent supergene evolution events in mating-type chromosomes. Nature Communications 9:2000.

3 Bazzicalupo A, Carpentier F, Otto S and Giraud T (2019) No evidence of antagonistic selection in the evolutionary strata of fungal mating-type chromosomes (Microbotryum lychnidis-dioicae) G3 9: 1987-1998.