Characterization of mating type (MAT) alleles differentiated by a natural inversion in Sclerotinia minor

Abstract

A recent study on fungal mating type genes revealed two MAT alleles within homothallic Sclerotinia sclerotiorum differentiated by an inversion, Inv− (inversion negative) and Inv+ (inversion positive). An analysis of mating type in closely related S. minor was conducted to shed light on the evolution of this MAT inversion. Inv− and Inv+ MAT alleles were identified in S. minor and were characterized. Both MAT alleles in S. minor were flanked by APN2 and SLA2, and consisted of two idiomorphs fused as in other homothallic ascomycetes. However, in the Inv+ MAT, the 3·6 kb MAT region was inverted relative to the Inv− MAT. Except for the inversion, both Inv− and Inv+ MAT in S. minor were equal in size and identical in nucleotide sequence. The MAT inversion in Inv+ S. minor was at exactly the same place as in Inv+ S. sclerotiorum and affected three of four MAT genes: MAT1‐1‐1 was truncated and MAT1‐2‐4 and MAT1‐2‐1 were inverted. Unlike S. sclerotiorum, expression of MAT genes did not differ between Inv− and Inv+ S. minor. The 250 bp inverted repeat motif that flanked the inverted MAT region in S. sclerotiorum and believed responsible for the MAT inversion was also found in S. minor, but was 256 bp. Depending on the MAT genes, 93–96% nucleotide identity was observed between Sclerotinia species. Both Inv+ and Inv− MAT S. minor and S. sclerotiorum isolates were commonly found in lettuce fields of Arizona along with MAT heterokaryons.

Characterization of the Mycelial Compatibility Groups and Mating Type Alleles in Populations of Sclerotinia minor in Central China

“…S3 and S4). The DNA sequences for Inv-and Inv+ obtained in this study were 99% identical to the corresponding DNA sequences reported by Chitrampalam and Pryor (2015). Based on the MAT alleles, the 95 isolates of S. minor from central China were classified into three groups, Inv-, Inv+, and heterokaryon (Inv-plus Inv+), which accommodated 4, 56, and 35 isolates (accounting for 4, 59, and 37% of the total 95 isolates), respectively (Table 4).…”

“…Amplification of the internal transcribed spacer (ITS) of the ribosomal DNA with the primer pair ITS1/ITS4 (White et al 1990) was used as control to check for DNA quality. The PCR was done in Bio-RAD S1000 Thermal Cycler using the program described by Chitrampalam and Pryor (2015). The resulting PCR fragments (539, 674, and 1,348 bp for ITS, Inv-, and Inv+, respectively), were detected by agarose gel electrophoresis.…”

“…The DNA fragments amplified from isolates XN01 (Inv-), XN02 (Inv-), DY02 (Inv+), LC41 (Inv+), XN19 (heterokaryon), and XN34 (heterokaryon) were individually cloned in E. coli using the pMD18-T vector (TaKaRa Biotechnology Co. Ltd., Dalian, China) and sequenced. The resulting DNA sequences were aligned with the corresponding DNA sequences for Inv-and Inv+ in isolates SM1 (Inv-) and SM24 (Inv+) of S. minor (Chitrampalam and Pryor 2015).…”

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

“…The structure of the mating type locus in S. minor and S. sclerotiorum has been characterized1617. Although both S. sclerotiorum and S. minor are homothallic, they have two mating type alleles differentiated by a natural inversion of about 3.6-kb DNA, designated as Inv− and Inv+  MAT alleles1617.…”

“…Although both S. sclerotiorum and S. minor are homothallic, they have two mating type alleles differentiated by a natural inversion of about 3.6-kb DNA, designated as Inv− and Inv+  MAT alleles1617. Each allele contains four MAT genes including MAT1-1-1 , MAT1-1 -5, MAT1-2-1 and MAT1-2-4 .…”