Characterization and phylogenetic analysis of the mating-type loci in the asexual ascomycete genusUlocladium

Abstract

The genus Ulocladium is thought to be strictly asexual. Mating-type (MAT) loci regulate sexual reproduction in fungi and their study may help to explain the apparent lack of sexual reproduction in Ulocladium. We sequenced the full length of two MAT genes in 26 Ulocladium species and characterized the entire MAT idiomorphs plus flanking regions of Ulocladium botrytis. The MAT1-1 ORF encodes a protein with an alpha-box motif by the MAT1-1-1 gene and the MAT1-2 ORF encodes a protein with an HMG box motif by the MAT1-2-1 gene. Both MAT1-1-1 and MAT1-2-1 genes were detected in a single strain of every species. Moreover, the results of RT-PCR revealed that both MAT genes are expressed in all 26 Ulocladium species. This demonstrates that MAT genes of Ulocladium species might be functional and that they have the potential for sexual reproduction. Phylogenies based on MAT genes were compared with GAPDH and Alt a 1 phylograms in Ulocladium using maximum parsimony (MP) and Bayesian analysis. The MAT genealogies and the non-MAT trees displayed different topologies, indicating that MAT genes are unsuitable phylogenetic markers at the species level in Ulocladium. Furthermore, the conflicting topologies between MAT1-1-1 and MAT1-2-1 phylogeny indicate separate evolutionary events for the two MAT genes. However, the intergeneric phylogeny of four closely allied genera (Ulocladium, Alternaria, Cochliobolus, Stemphylium) based on MAT alignments demonstrated that MAT genes are suitable for phylogenetic analysis among allied genera.

Mating-type genes of the anamorphic fungus Ulocladium botrytis affect both asexual sporulation and sexual reproduction

“…We have previously cloned and described the structural organization of MAT1-1-1 and MAT1-2-1 from the asexual species U. botrytis 30 . To test the functions of MAT1-1-1 and MAT1-2-1 genes in U. botrytis , we created MAT1-1-1 or MAT1-2-1 , and MAT1-1-1 / 1-2-1 deletion mutants using the split-marker method.…”

“…Fungi are a group historically considered to present a high proportion of asexual species; a fifth of the species were once thought to exclusively reproduce asexually 41 . For example, most species in the filamentous ascomycetes genera Alternaria , Stemphylium , and Ulocladium are only known to reproduce asexually 29 , 30 . Possible reasons for the absence of sex are that the suitable factors and conditions needed to induce sex have not been determined and further research needs to be conducted to identify suitable environmental conditions for sex, or that these fungal genomes lack the equipment to engage in sex 42 , 43 .…”

“…Previously, we identified the full-length sequences of MAT1-1-1 and MAT1-2-1 genes for 26 Ulocladium species. Notably, both MAT1-1-1 and MAT1-2-1 genes were detected in the same haploid genome of all 26 Ulocladium species which appear to similar to that of Ophiocordyceps sinensis 40 , and thus all of the Ulocladium species have the potential to be homothallic 30 . Transcriptional analysis on the basis of qRT-PCR showed that both MAT1-1-1 and MAT1-2-1 genes were expressed and may be functional in all 26 Ulocladium species, suggesting that all these Ulocladium species might have the potential to reproduce sexually 30 .…”

Characterization and distribution of mating-type genes of the turfgrass pathogen Sclerotinia homoeocarpa on a global scale

“…Several filamentous fungi have been shown to possess MAT1-1-1 and MAT1-2-1 at unlinked loci, the characteristic MAT1 locus and a second, MAT2 (Bushley et al, 2013;Galagan et al, 2005;Geng et al, 2014;Gioti et al, 2012;Paoletti et al, 2007;Pöggeler et al, 2011;Rydholm et al, 2007;Yun et al, 1999). Our discovery of a truncated, degenerated copy of MAT1-2-1 located elsewhere in the genome of MAT1-1 isolate MB-01 allows for the possibility of a similar phenomenon occurring in historical type strains such as ATCC 10942 and IMI 167641.…”

Mating System in the Brown Rot Pathogens Monilinia fructicola, M. laxa, and M. fructigena

“…A low genetic diversity is expected in chromosomal regions carrying the MAT idiomorphs because recombination is supposed to be suppressed and rare at the MAT1 locus in Ascomycetes (Idnurm 2011). Mating-type gene sequences have been frequently used as markers in phylogenetic studies or to establish species boundaries in different genera of Ascomycetes (Lopes et al 2017;O'Donnell et al 2004), although several authors found them of limited utility (Geng et al 2014;Strandberg et al 2010). The three Monilinia species showed high similarity of the sequences of genes and intergenic regions within the MAT1-1 and MAT1-2 idiomorphs while it was lower in the bordering regions.…”