Identification and characterization of mating type (MAT) alleles in Sclerotinia minor
P. CHITRAMPALAM (1), B. Pryor (2). (1) North Dakota State University, Fargo, ND, U.S.A.; (2) University of Arizona, Tucson, AZ, U.S.A.
Recently, two <i>MAT</i> alleles that differed by the presence of an inversion [inversion negative (Inv-) and inversion positive (Inv+)] have been characterized in homothallic <i>Sclerotinia sclerotiorum</i>. We identified and characterized both <i>MAT</i> alleles in <i>S. minor</i> as well. Both Inv- and Inv+ <i>MAT</i> alleles in <i>S. minor</i> were 100% identical in structure to their corresponding <i>MAT</i> allele in <i>S. sclerotiorum</i>, and both <i>MAT</i> alleles were flanked between the putative <i>APN2</i> and <i>SLA2</i> at 5’ and 3’ end, respectively. <i>MAT</i> genes were arranged as <i>MAT1-1-5</i>, <i>MAT1-1-1</i>, <i>MAT1-2-4</i> and <i>MAT1-2-1</i> in Inv- <i>MAT</i>. However, in Inv+ <i>MAT</i>, a 3.6-kb region is inverted in relative to Inv- <i>MAT</i>, and as a result <i>MAT1-1-1</i> is truncated at the 3’ end and the orientation of <i>MAT1-2-4</i> and <i>MAT1-2-1</i> has changed. Inverted repeat motifs (250 bp) believed to be the driving force for <i>MAT</i> inversion in <i>S. sclerotiorum</i> have also been found in <i>S. minor</i> as flanks of <i>MAT</i> inverted region. However, the size was 256 bp in <i>S. minor</i>. <i>MAT</i> genes in <i>S. minor</i> were 93-96 % identical to their homologues in <i>S. sclerotiorum</i>. Among the non-coding flanks of <i>MAT</i> genes, the 5’-<i>MAT1-1-5</i> flank was the most variable between species, and it was1377-bp shorter in <i>S. minor</i>. The expression of <i>MAT</i> genes did not differ between Inv- and Inv+ isolates. The phylogeny of <i>MAT</i> genes revealed that <i>MAT</i> inversion occurred independently in each species. Of 38 <i>S. minor</i> isolates screened, 50%, 8%, and 42 % isolates were Inv-, Inv+ and heterokaryon for <i>MAT</i>, respectively.
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