Mating system of the filamentous ascomycete, Glomerella cingulata

Abstract

Mating in heterothallic filamentous ascomycetes is typically controlled by a single mating-type locus with two alternate alleles or idiomorphs. In this study, five self-sterile strains of Glomerella cingulata from pecan were crossed in all possible combinations. Four of the five strains could be placed into two mating-type groups, but the fifth strain was sexually compatible with all of the other strains. Single ascospore progeny were isolated from each of the successful crosses, tested for self-fertility, and backcrossed with both parents. In addition, subsets of F1 isolates were crossed with all five of the original strains from pecan and in all possible combinations with each other. Results from the crosses showed that the ascospore progeny had stably inherited the mating pattern of one of the parental strains and that the mating type had segregated 1:1 among the F1 isolates. Furthermore, the five strains from pecan were sexually compatible with five additional heterothallic strains in all but one combination. Data from these experiments are consistent with a mating system composed of a single mating-type locus with multiple alternate alleles. We believe that this is the first report of this type of mating system for an ascomycete species.

Analysis of the MAT1-2-1 gene of Colletotrichum lindemuthianum

“…As already mentioned, mating pairs of most fi lamentous ascomycetes carry either the MAT1-1 or the MAT1-2 idiomorph at the MAT1 locus; however, as shown here and in other reports in the genus Glomerella (Cisar et al 1996;Cisar and TeBeest 1999;Vaillancourt et al 2000;Rodríguez-Guerra et al 2005), both mating partners carry the MAT1-2 idiomorph. However, if one of the partners in the Glomerella mating pair carries a defective MAT1-2 idiomorph or nontranscribed MAT1-2-1 gene, this would effectively reproduce the situation in other fi lamentous ascomycetes in which a functional MAT1-2 idiomorph is present in only one member of the mating pair (Glass et al 1988) and be in agreement with the model proposed by Wheeler (1954).…”

“…Cisar and TeBeest (1999) reported that in G. cingulata multiple alleles occur at MAT1-2, which would also agree with the unbalanced heterothallism model if mutations between strains occurred mainly within this locus. The presence of the MAT1-1 idiomorph has not been reported for any member of the genus Glomerella to date.…”

“…Sacc.) and more recent reports on different species within the genus Glomerella (Cisar et al 1996;Cisar and TeBeest 1999;Vaillancourt and Hanau 1999;Vaillancourt et al 2000;Rodríguez-Guerra et al 2005) suggest that control of sexual reproduction within this genus is different from that described for other fi lamentous ascomycetes.…”

Evolution of uni- and bifactorial sexual compatibility systems in fungi

“…However, all unifactorial Basidiomycete species for which this has been investigated show genomic signatures that they evolved secondarily from a bifactorial system (see the section 'Reversion to unifactorial mating ' and Kües et al, 2011), which would thus be ancestral in the Basidiomycete clade. Similarly, all known fungal species with multiple mating-type alleles belong to Basidiomycetes-again except one case (Cisar and TeBeest, 1999). We therefore consider that the bifactorial mating system arose once and from a biallelic unifactorial system, either by first acquiring multiple alleles followed by acquisition of a second mating-type locus, or by first evolving a bifactorial mating-type system that then became multiallelic in many species.…”

Sexual selection in fungi

“…Almost all heterothallic ascomycetes have a system with two different mating types, which usually implies that each individual is compatible with half the population (if both mating types occur in equal frequencies, which is the case whenever sexual reproduction occurs frequently). Many Basidiomycota (especially the mushroomforming ones; Kü es et al, 2011), some Physarum species (Collins, 1975) and at least one ascomycete Gibberella cingulata (Cisar & TeBeest, 1999) have a system with more than two, sometimes up to hundreds, different mating types (see also 'Sexual Selection in Mushroom Fungi' in the main text). In a population with many mating types, gametes are compatible with almost all unrelated gametes in a population.…”