ARS | Publication request: Identification and structure of the mating-type locus and development of PCR-based markers for mating type in powdery mildew fungi

Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 5, 2011
Publication Date: July 15, 2011
Citation: Brewer, M.T., Cadle Davidson, L.E., Cortesi, P., Spanu, P.D., Milgroom, M.G. 2011. Identification and structure of the mating-type locus and development of PCR-based markers for mating type in powdery mildew fungi. Fungal Genetics and Biology. 48:704-713.

Interpretive Summary: The grape powdery mildew fungus uses sexual reproduction between two individuals of opposite mating type to form overwintering structures. It is impossible to visually inspect a powdery mildew and know which mating type it is, but if we knew the genes involved, we could identify each mating type with a DNA assay. Therefore, the objectives of this study were to identify and sequence mating-type genes in the grape powdery mildew fungus. We used genome sequence analysis to successfully identify both mating type DNA sequences (called MAT1-1 and MAT1-2). We developed and applied a reliable DNA assay that successfully predicted which of 100 grape powdery mildew isolates would mate with tester lines of known mating type. The mating-type genes in grape powdery mildew are similar to other fungi; however, unlike other fungi, the DNA sequence length is greatly expanded and may be riddled with junk DNA and jumping genes known as transposons. As a result, we were unable to sequence either MAT1-1 or MAT1-2 in its entirety. However, from this information, we designed a DNA assay that could be used to identify and sequence mating type genes in any powdery mildew.

Technical Abstract: In fungi, mating compatibility is regulated by mating-type loci. The objectives of this study were to identify and sequence mating-type genes at the MAT1 locus in the grape powdery mildew fungus, Erysiphe necator, to develop a PCR-based marker for determining mating type in E. necator, and to develop degenerate primers for PCR-amplification of conserved regions of both mating type idiomorphs in other powdery mildews. We identified MAT1-2-1 of the MAT1-2 idiomorph based on sequences of this gene in the B. graminis f. sp. hordei genome and MAT1-1-1 and MAT1-1-3 of the MAT1-1 idiomorph from transcriptome sequence of E. necator. We developed and applied a reliable PCR-based multiplex marker to confirm that genotype correlated with mating phenotype, which was determined for 100 isolates from the eastern United States and Italy by pairing with compatible tester isolates of each mating type. The mating-type genes in E. necator are similar to other Leotiomycetes; however, unlike other ascomycetes, the MAT1 locus in E. necator is greatly expanded and may be riddled with repetitive DNA. As a result, we were unable to amplify and sequence either idiomorph in its entirety. Degenerate primers that amplify conserved regions of MAT1-1 and MAT1-2 across the genera Erysiphe, Podosphaera, Microsphaera, and Blumeria of the Erysiphales were designed; these primers could be used to identify and sequence MAT1 genes or design mating-type markers in any powdery mildew.