Structure and evolution of the Fusarium mating type locus: New insights from the Gibberella fujikuroi complex

Abstract

Mating type genes are central to sexual reproduction and compatibility in Ascomycete fungi. However the "MAT" loci experience unique evolutionary pressures that can result in rapid divergence and enhanced inter-specific gene-flow (lateral gene transfer). In this study, molecular evolution of MAT loci was considered using the genus Fusarium (Teleomorph: Gibberella) as a model. Both MAT1-1 and MAT1-2 "idiomorphs" from eleven species of the Gibberella fujikuroi species complex were sequenced. Molecular evolution of the MAT loci from these heterothallic (self-sterile) species was compared with that of the MAT loci from nine homothallic (self-fertile) species in the Fusarium graminearum species complex. Although Fusarium has previously been thought to have the same complement of four MAT genes that are found in Neurospora, we found evidence of a novel gene, MAT1-2-3, that may be specific to the Hypocreales. All MAT genes share a similar set of cis-regulatory motifs, although homothallic species might have recruited novel regulatory elements, which could potentially facilitate alternate expression of MAT1-1-1 and MAT1-2-1. Fusarium MAT loci displayed evidence consistent with historical lateral gene-flow. Most notably, the MAT1-1 idiomorph of Fusarium sacchari appears to be unrelated to those of other species in the G. fujikuroi complex. In general, Fusarium MAT genes are highly divergent. Both positive selection and relaxed selective constraint could account for this phenomenon. However, the extent of both recombination and inter-specific gene-flow in the MAT locus also appears to affect the rate of divergence.

Characterization of the mating-type genes in Leptographium procerum and Leptographium profanum

“…with similar order and orientation to those of Gibberella fujikuroi, Fusarium oxysporum (Martin et al 2011;Yun et al 2000), Cryphonectria parasitica (McGuire et al 2001), Podospora anserina (Debuchy et al 1993) and Neurospora crassa (Ferreira et al 1996). The sequences of MAT1-1 genes in these two fungi are very similar and correspond with those known in other…”

“…MAT1-2 usually contains a single MAT1-2-1 gene encoding for a protein with a high mobility group (HMG) domain (Coppin et al 1997;Turgeon and Yoder 2000), but in some cases a second gene (mat a-2, MAT1-2-2; MAT1-2-3 or MAT1-2-4) can be found within the MAT1-2 idiomorph (Amselem et al 2011;Kanamori et al 2007;Martin et al 2011;Pöggeler and Kück 2000). In contrast to heterothallic fungi, isolates of homothallic species harbor both MAT1-1 and MAT1-2 regions in their genomes, and sexual reproduction can occur in the absence of a second isolate (Nelson 1996).…”

Fusarium in the age of genomics

“…Martin et al 2011). A major drawback of this species concept is the fact that many Fusarium species have no known sexual cycle.…”

MAT gene idiomorphs suggest a heterothallic sexual cycle in a predominantly asexual and important pine pathogen

“…In Ascomycetes, sexual reproduction between individuals of the same species is governed by the genes found at a single mating type locus (MAT-1), which contains two core gene families (MAT1-1 and MAT1-2) (Turgeon, 1998;Turgeon and Yoder, 2000;Lee et al, 2010;Debuchy et al, 2010;Ni et al, 2011). In heterothallic species, individuals contain only one of the two gene families at the MAT-1 locus (idiomorphs), and require an individual of the opposite MAT-1 idiomorph for sexual reproduction (Kronstad and Staben, 1997;Groenewald et al, 2008;Lee et al, 2010;Martin et al, 2011). The MAT1-1 idiomorph contains at least a MAT1-1-1 gene that encodes a protein with an α-1 box domain.…”