The dynamics of evolution in plant and fungal interactions - from communities to genomes
Stukenbrock, Eva H. , McDonald, Bruce A. , Grønlund-Jørgensen, Frank , Heide, Mikkel S. .
Deciphering the genetic basis of speciation of a fungal plant pathogen through comparative genomics.
Comparative genomics provides a powerful framework for studies of molecular evolution of fungal pathogens. The aim of the present study is to decipher patterns of genome evolution during speciation of the wheat pathogen Mycosphaerella graminicola. We compared the genome sequence of M. graminicola to the genome of a closely related pathogen infecting wild grasses, here named S1. Previous coalescence studies have shown that these two pathogens diverged 10-11,000 years ago in the Fertile Crescent, coinciding with domestication of wheat. We sequenced the genome of S1 using Illumina Sequencing to an average coverage of 32X. Paired end reads were assembled using a de novo assembly approach and subsequently aligned to the genome of M. graminicola. The alignment covered approximately 71% of the 21 M. graminicola chromosomes and showed a high nucleotide identity (90-95%) consistent with a recent coalescence of the pathogen lineages. However, in spite of high sequence similarity the two genomes have undergone considerable structural rearrangements. In M. graminicola such chromosomal rearrangements have in particular affected the dispensable chromosomes 14-21. Both genomes contain 4-5Mb of unique non-repetitive DNA that cannot be aligned and may be organized in the dispensable chromosomes of M. graminicola and in S1 specific chromosomes. Estimates of synonymous substitution rates across chromosomes showed a lower rate in the dispensable chromosomes compared to the essential chromosomes. Additionally, these chromosomes showed an accumulation of repetitive DNA and were enriched in genes with dN/dS > 1. This pattern of chromosome evolution resembles the pattern observed in plant B-chromosomes and in univalent sex chromosomes and is likely in part due to a reduced effective population size of the dispensable chromosomes. The genomic comparison of essential and dispensable chromosomes in S1 and M. graminicola provides an ideal model system to study the role, evolution and dynamics of dispensable chromosomes in pathogens.
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1 - Aarhus University, Bioinformatics Research Center, C.F. Moellers Alle 8, Aarhus, DK-8000, Denmark
2 - ETH Zurich, Plant Pathology, Inst of Integrative Biology, Universitaetstr 2, Zurich, CH-8092, Switzerland
Presentation Type: Symposium or Colloquium Presentation
Location: Ballroom 3/Cliff Lodge - Level B
Date: Monday, July 27th, 2009
Time: 11:00 AM