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ARS Home » Pacific West Area » Pullman, Washington » Grain Legume Genetics Physiology Research » Research » Publications at this Location » Publication #327322

Research Project: Genetic Improvement of Cool Season Food Legumes

Location: Grain Legume Genetics Physiology Research

Title: Direct repeat-mediated DNA deletion of the mating type locus MAT1-2 genes results in unidirectional mating type switching in Sclerotinia trifoliorum

Author
item Xu, Liangsheng - Washington State University
item Chen, Weidong

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2016
Publication Date: 6/3/2016
Citation: Xu, L., Chen, W. 2016. Direct repeat-mediated DNA deletion of the mating type locus MAT1-2 genes results in unidirectional mating type switching in Sclerotinia trifoliorum. Scientific Reports. 6:27083.

Interpretive Summary: The fungus Sclerotinia trifoliorum is a pathogen of chickpea and other cool season legumes, and it produces spores of two sizes. The large spores give rise to strains that are self-fertile and produce large and small spores again, but the small spores give rise to strains that are self sterile and cannot produce any spores. This phenomenon is called unidirectional mating type switching. The mechanisms of unidirectional mating type switching in S. trifoliorum are not understood. The present study, comparing DNA sequences in the DNA region (MAT locus) that controls mating and spore production, found four main mating type genes (MAT1-1-5, MAT1-1-1, MAT1-2-1 and MAT1-2-4) in the self-fertile strain derived from large spores. In contrast, this DNA region in the self-sterile strain derived from small spores is 2891-bp shorter than that of the self-fertile strains. Within the missing DNA are the entire MAT1-2-1 and MAT1-2-4 genes. Thus the self-sterile strains do not contain the MAT1-2 genes and that is why they are self-sterile. Meanwhile, a146-bp DNA sequence was found repeated twice and the two repeats flank the deleted region in the self-fertile strains. The two repeat sequences were believed to be responsible for the deletion through homologous recombination during meiosis. Tetrad (ordered spore) analyses showed that all small spore-derived strains lacked the missing DNA between the two direct repeats that was found in all large spore-derived strains. In addition, many isolates including single-spore isolates were found to be heterokaryotic at the MAT locus, suggesting that such direct-repeats mediated deletion may also occur during mitosis at low frequencies.

Technical Abstract: The fungus Sclerotinia trifoliorum is a pathogen of chickpea and other cool season legumes, and it produces spores of two sizes. The large spores give rise to strains that are self-fertile and produce large and small spores again, but the small spores give rise to strains that are self sterile and cannot produce any spores. This phenomenon is called unidirectional mating type switching. The mechanisms of unidirectional mating type switching in S. trifoliorum are not understood. The present study, comparing DNA sequences in the DNA region (MAT locus) that controls mating and spore production, found four main mating type genes (MAT1-1-5, MAT1-1-1, MAT1-2-1 and MAT1-2-4) in the self-fertile strain derived from large spores. In contrast, this DNA region in the self-sterile strain derived from small spores is 2891-bp shorter than that of the self-fertile strains. Within the missing DNA are the entire MAT1-2-1 and MAT1-2-4 genes. Thus the self-sterile strains do not contain the MAT1-2 genes and that is why they are self-sterile. Meanwhile, a146-bp DNA sequence was found repeated twice and the two repeats flank the deleted region in the self-fertile strains. The two repeat sequences were believed to be responsible for the deletion through homologous recombination during meiosis. Tetrad (ordered spore) analyses showed that all small spore-derived strains lacked the missing DNA between the two direct repeats that was found in all large spore-derived strains. In addition, many isolates including single-spore isolates were found to be heterokaryotic at the MAT locus, suggesting that such direct-repeats mediated deletion may also occur during mitosis at low frequencies.