Abstract Detail

Poster Session

McCotter, Sean W. [1], Humann, Jodi L. [2], Main, Dorrie [2], Okubara, Patricia A. [1], Carris, Lori [1], Castlebury, Lisa A. [3].

The bipolar-mating wheat bunt pathogen, Tilletia caries, possesses an unusual complement of mating genes.

The genus Tilletia (Basidiomycota, Ustilaginomycotina,) includes common, dwarf and Karnal bunt pathogens of wheat. The role of the mating system is of fundamental importance in the bunt life cycle and to pathogenicity because mating is a prerequisite for plant infection. Mating systems in Basidiomycota are termed bipolar in the case of mating-gene (MAT) linkage and tetrapolar in the case of non-linkage. In bipolar mating members of Ustilaginomycotina such as Ustilago hordei, MAT-genes are organized into two subloci, one encoding two homeodomain transcription factors and the other encoding pheromones and a G-protein-coupled pheromone receptor. Different mating types possess alleles of alternative specificity at these subloci which determine sexual compatibility. These MAT-genes have thus far not been molecularly characterized in Tilletiales. Prior studies utilizing crosses identified a bipolar mating system in wheat bunt species; two mating type alleles were identified in common bunt species T. caries and T. laevis and multiple alleles were identified in dwarf and Karnal bunt species T. contraversa and T. indica. The objectives of this study were identification and characterization of genes at the mating locus in T. caries. Whole genome sequencing of T. caries strain 517 on PacBio RS and Roche 454 platforms was followed by assembly with Allora (PacBio SMRT-analysis) and gene prediction with FGENESH and AUGUSTUS algorithms. A homology-based approach was used to identify the two MAT-subloci. Each sublocus was re-sequenced with Sanger sequencing to verify assembly accuracy. Putative pheromone precursor and pheromone receptor orthologs as well as three putative homeodomain transcription factors (one bE and two bW orthologs), were annotated in silico. Intron-exon splice sites are currently being verified via PCR using cDNA. MAT-gene transcripts are being quantified in vitro via RT-qPCR. Additional avenues of research include further PacBio sequencing of strain 517 to increase coverage and resolve single chromosomes, the construction of heterologous system assays to verify function of the homeodomain transcription factors in vivo and sequencing of MAT-genes in a strain of compatible mating type to T. caries 517. We hypothesize that the compatible mating type will possess the reciprocal arrangement of homeodomain transcription factors at the MAT-b sublocus (i.e. two bE and one bW gene). The possible presence of three homeodomain transcription factors at the MAT-b sublocus instead of the classical two gene system found in other smut fungi is unprecedented and demands further investigation, especially regarding the relative levels of expression for these genes.

1 - Washington State University, Plant Pathology, PO Box 646430, Washington State University, Pullman, WA, 99164-6430, USA
2 - Washington State University, Horticulture, PO Box 646414, Washington State University, Pullman, WA, 99164-6414, USA
3 - USDA Agricultural Research Service, Systematic Mycology and Microbiology, 10300 Baltimore Avenue, BLDG 010A BARC-WEST, Beltsville, MD, 20705-0000, USA

Keywords:
Mating systems
basidiomycetes
Genome
Smuts.

Presentation Type: Offered Paper - Poster
Session: P3
Location: Lincoln Room/Kellogg Hotel and Conference Center
Date: Monday, June 9th, 2014
Time: 8:00 PM
Number: P3004
Abstract ID:174
Candidate for Awards:Graduate Student Poster Presentation Award