Data from: Repeated loss of function at HD mating-type genes and of recombination suppression without mating-type locus linkage in anther-smut fungi

A wide diversity of mating systems occur in nature, with frequent
evolutionary transitions in mating-compatibility mechanisms. Basidiomycete
fungi typically have two mating-type loci controlling mating
compatibility, HD and PR, usually residing on different chromosomes. In
Microbotryum anther-smut fungi, there have been repeated events of linkage
between the two mating-type loci through chromosome fusions, leading to
large non-recombining regions. By generating high-quality genome
assemblies, we found that two sister Microbotryum species parasitizing
Dianthus plants, M. superbum and M. shykoffianum, as well as the distantly
related M. scorzonarae, have their HD and PR mating-type loci on different
chromosomes, but with the PR mating-type chromosome fused with part of the
ancestral HD chromosome. Furthermore, progressive extensions of
recombination suppression have generated evolutionary strata. In all three
species, rearrangements suggest the existence of a transient stage of
HD-PR linkage by whole chromosome fusion, and, unexpectedly, the HD genes
lost their function. In M. superbum, multiple natural diploid strains were
homozygous, and the disrupted HD2 gene was hardly expressed. Mating tests
confirmed that a single genetic factor controlled mating compatibility
(i.e. PR) and that haploid strains with identical HD alleles could mate
and produce infectious hyphae. The HD genes have therefore lost their
function in the control of mating compatibility in these Microbotryum
species. While the loss of function of PR genes in mating compatibility
has been reported in a few basidiomycete fungi, these are the first
documented cases for the loss of mating-type determination by HD genes in
heterothallic fungi. The control of mating compatibility by a single
genetic factor is beneficial under selfing and can thus be achieved
repeatedly, through evolutionary convergence in distant lineages,
involving different genomic or similar pathways.