MAT gene idiomorphs suggest a heterothallic sexual cycle in a predominantly asexual and important pine pathogen.
Diplodia pinea (=Sphaeropsis sapinea) is a well-known and economically important latent pathogen of Pinus spp. in many parts of the world. Despite intensive scrutiny, its sexual state has never been observed and the fungus has thus been considered exclusively asexual. It was, therefore, surprising that a recent population genetics study showed high genotypic diversity and random association of alleles in a number of populations, suggesting that the pathogen has a cryptic sexual stage. Using the genome sequence of two individual D. pinea isolates, we interrogated the structure of the MAT locus in this fungus. The results suggested that D. pinea is heterothallic (self-sterile) with complete and apparently functional copies of the MAT genes containing the α-1 and HMG domains present in different isolates. In addition to the MAT1-2-1 and MAT1-1-1 genes, we found a MAT1-1-4 gene in the MAT1-1 idiomorph and a novel MAT1-2-5 gene in the MAT1-2 idiomorph. Importantly, the frequencies of occurrence of both idiomorphs in populations examined were not significantly different from a 1:1 ratio, which would be expected in sexually reproducing populations. Although the sexual state has never been observed, the results strongly suggest that D. pinea has a cryptic, heterothallic sexual cycle.
Department of Genetics, Forestry and Agricultural Biotechnology Institute, University of Pretoria, Private Bag X20, Hatfield, Pretoria 0028, South Africa; Crop Protection Division, Vegetable and Ornamental Plant Institute, Agricultural Research Council, Private Bag X293, Pretoria 0001, South Africa. Electronic address: LegesseW@arc.agric.za.
Wubetu
W
Bihon
Department of Genetics, Forestry and Agricultural Biotechnology Institute, University of Pretoria, Private Bag X20, Hatfield, Pretoria 0028, South Africa.
Michael J
MJ
Wingfield
Department of Genetics, Forestry and Agricultural Biotechnology Institute, University of Pretoria, Private Bag X20, Hatfield, Pretoria 0028, South Africa.
Bernard
B
Slippers
Department of Genetics, Forestry and Agricultural Biotechnology Institute, University of Pretoria, Private Bag X20, Hatfield, Pretoria 0028, South Africa.
Tuan A
TA
Duong
Department of Genetics, Forestry and Agricultural Biotechnology Institute, University of Pretoria, Private Bag X20, Hatfield, Pretoria 0028, South Africa.
Brenda D
BD
Wingfield
D000595:Amino Acid Sequence; D004271:DNA, Fungal / Q000737:chemistry* / Q000235:genetics*; D005658:Fungi / Q000235:genetics*; D049770:Genes, Mating Type, Fungal; D024742:HMG-Box Domains; D008969:Molecular Sequence Data; D010802:Phylogeny; D028223:Pinus / Q000469:parasitology*; D017434:Protein Structure, Tertiary; D012100:Reproduction, Asexual
D004271:DNA, Fungal
Cryptic sex; Diplodia pinea; Endophyte; Heterothallic; Idiomorph; Mating type