Abstract Detail

Host/Plant Pathogen Interactions and Plant Health Management

Cheung, Hoi Yee Kitty [1], Doyle, Colleen [1], Donaldson, Michael [2], Spence, Kelsey [3], Saville, Barry [4].

Plant pathogenesis, sex, and smut fungi.

Ustilago maydis is the model for basidiomycete biotrophic plant pathogenesis. Its pathogenic/sexual cycle begins with the fusion of compatible non-pathogenic haploid cells to form a filamentous pathogenic dikaryon, which grows in the plant, eliciting the formation of tumours within which teliospores develop. Teliospores are the only U. maydis cell type capable of completing meiosis. Key to understanding smut pathogenesis is determining how the fungus controls developmental changes during growth and sexual development within the host plant. Annotation of the U. maydis genome identified two transcription factors, Mcg1 and Zfp1, which are orthologs of the Saccharomyces cerevisiae meiotic control proteins, NDT80 and UME6, respectively. NDT80 and UME6 are indispensable for normal meiotic progression in S. cerevisiae and it was hypothesized that their U. maydis orthologs would have similar functions. Our investigations revealed that mcg1 is involved in meiosis and that zfp1 is not involved in meiosis, but has a controlling role in pathogenic development. Deletion of mcg1 (meiosis control gene 1) did not alter pathogenesis as determined by seeding assay, but arrested the maturation and pigmentation of teliospores, as well as the completion of meiosis. In certain media, we found that constitutive expression of mcg1 resulted in abnormal pigmentation and rounding of haploid cells. Analysis of the Mcg1 DNA-binding domain and identification of conserved motifs upstream of putative target genes revealed that Mcg1 has similar DNA-binding properties to NDT80, suggesting that it functions as a transcription factor. The data shows Mcg1 is crucial for the maturation and pigmentation of teliospores, and for meiotic competence in U. maydis. Deletion of zfp1 (zinc finger protein 1) did not have an effect on meiosis, but led to a reduction in pathogenesis and anthocyanin levels. Anthocyanin production is a sign of fungal penetration, and microscopic analysis of the zfp1 deletion strains in planta showed a delay in host penetration and that hyphal growth is localized in the leaf tissue. Comparative RNA-seq analysis identified a large number of confirmed or predicted effector coding genes with altered transcript levels. The data suggests Zfp1 is a transcription factor that is involved in pathogenesis through the regulation of effector genes. Our findings show that investigating U. maydis genes with orthologs linked to meiosis in other fungi is a productive means of gaining insight into the control of pathogenic development in U. maydis.

Related Links:
The Saville Laboratory

1 - Trent University, Environmental and Life Sciences Graduate Program, DNA Building, 2140 East Bank Dr, Peterborough, ON, K9J 7B8, Canada
2 - Trent University, Environmental and Life Sciences Graduate Program; Forensic Science Program, DNA Building, 2140 East Bank Dr, Peterborough, ON, K9J 7B8, Canada
3 - Ontario Veterinary College, University of Guelph, Department of Population Medicine, 50 Stone Road East, Guelph, ON, N1G 2W1, Canada
4 - Trent University, Environmental and Life Sciences; Forensic Science, DNA Building, 2140 East Bank Drive, Peterborough, ON, K9J 7B8, Canada

Keywords:
Ustilago maydis
Transcription factors
pathogenesis
Meiosis
Effectors
Teliospore pigmentation.

Presentation Type: Oral Paper:Papers for Topics
Session: 57
Location: Salon 9/The Shaw Conference Centre
Date: Wednesday, July 29th, 2015
Time: 9:15 AM
Number: 57006
Abstract ID:1193
Candidate for Awards:None