The heterothallic sugarbeet pathogen Cercospora beticola contains exon fragments of both MAT genes that are homogenized by concerted evolution.
Dothideomycetes is one of the most ecologically diverse and economically important classes of fungi. Sexual reproduction in this group is governed by mating type (MAT) genes at the MAT1 locus. Self-sterile (heterothallic) species contain one of two genes at MAT1 (MAT1-1-1 or MAT1-2-1) and only isolates of opposite mating type are sexually compatible. In contrast, self-fertile (homothallic) species contain both MAT genes at MAT1. Knowledge of the reproductive capacities of plant pathogens are of particular interest because recombining populations tend to be more difficult to manage in agricultural settings. In this study, we sequenced MAT1 in the heterothallic Dothideomycete fungus Cercospora beticola to gain insight into the reproductive capabilities of this important plant pathogen. In addition to the expected MAT gene at MAT1, each isolate contained fragments of both MAT1-1-1 and MAT1-2-1 at ostensibly random loci across the genome. When MAT fragments from each locus were manually assembled, they reconstituted MAT1-1-1 and MAT1-2-1 exons with high identity, suggesting a retroposition event occurred in a homothallic ancestor in which both MAT genes were fused. The genome sequences of related taxa revealed that MAT gene fragment pattern of Cercospora zeae-maydis was analogous to C. beticola. In contrast, the genome of more distantly related Mycosphaerella graminicola did not contain MAT fragments. Although fragments occurred in syntenic regions of the C. beticola and C. zeae-maydis genomes, each MAT fragment was more closely related to the intact MAT gene of the same species. Taken together, these data suggest MAT genes fragmented after divergence of M. graminicola from the remaining taxa, and concerted evolution functioned to homogenize MAT fragments and MAT genes in each species.
Northern Crop Science Laboratory, United States Department of Agriculture, Agricultural Research Service, Fargo, ND, United States. Electronic address: Melvin.Bolton@ars.usda.gov.
Melvin D
MD
Bolton
Department of Plant Systems Biology, VIB, Ghent, Belgium; Department of Plant Biotechnology and Bioinformatics, Ghent University, Ghent, Belgium.
Ronnie
R
de Jonge
Department of Plant Pathology, University of California, Davis, CA, United States.
Patrik
P
Inderbitzin
Department of Plant Pathology, North Dakota State University, Fargo, ND, United States.
Zhaohui
Z
Liu
Northern Crop Science Laboratory, United States Department of Agriculture, Agricultural Research Service, Fargo, ND, United States; Department of Phytopathology, Wageningen University, Wageningen, The Netherlands.
Keshav
K
Birla
Department of Plant Systems Biology, VIB, Ghent, Belgium; Department of Plant Biotechnology and Bioinformatics, Ghent University, Ghent, Belgium.
Yves
Y
Van de Peer
Department of Plant Pathology, University of California, Davis, CA, United States.
Krishna V
KV
Subbarao
Department of Phytopathology, Wageningen University, Wageningen, The Netherlands.
Bart P H J
BP
Thomma
Department of Plant Pathology, North Dakota State University, Fargo, ND, United States.
Gary A
GA
Secor
D001203:Ascomycota / Q000235:genetics*; D027461:Beta vulgaris / Q000382:microbiology*; D019143:Evolution, Molecular; D005091:Exons; D049770:Genes, Mating Type, Fungal; D012098:Reproduction
Cercospora; Concerted evolution; MAT; MAT1; MAT1-1, MAT1-2; MAT1-1-1; MAT1-2-1; Mating type; Retroposition; mating type gene encoding a protein with a high mobility group domain; mating type gene encoding an alpha box (α1) protein; mating type genes; mating type idiomorphs; mating type locus