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, 7 (2), R16

The Role of Transposable Element Clusters in Genome Evolution and Loss of Synteny in the Rice Blast Fungus Magnaporthe Oryzae

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The Role of Transposable Element Clusters in Genome Evolution and Loss of Synteny in the Rice Blast Fungus Magnaporthe Oryzae

Michael R Thon et al. Genome Biol.

Abstract

Background: Transposable elements are abundant in the genomes of many filamentous fungi, and have been implicated as major contributors to genome rearrangements and as sources of genetic variation. Analyses of fungal genomes have also revealed that transposable elements are largely confined to distinct clusters within the genome. Their impact on fungal genome evolution is not well understood. Using the recently available genome sequence of the plant pathogenic fungus Magnaporthe oryzae, combined with additional bacterial artificial chromosome clone sequences, we performed a detailed analysis of the distribution of transposable elements, syntenic blocks, and other features of chromosome 7.

Results: We found significant levels of conserved synteny between chromosome 7 and the genomes of other filamentous fungi, despite more than 200 million years of divergent evolution. Transposable elements are largely restricted to three clusters located in chromosomal segments that lack conserved synteny. In contradiction to popular evolutionary models and observations from other model organism genomes, we found a positive correlation between recombination rate and the distribution of transposable element clusters on chromosome 7. In addition, the transposable element clusters are marked by more frequent gene duplications, and genes within the clusters have greater sequence diversity to orthologous genes from other fungi.

Conclusion: Together, these data suggest that transposable elements have a profound impact on the M. oryzae genome by creating localized segments with increased rates of chromosomal rearrangements, gene duplications and gene evolution.

Figures

Figure 1
Figure 1
Distribution of sequence features on chromosome 7. Chromosome 7 was divided into non-overlapping 100 kb segments. The vertical axis of each chart represents the number of features per segment after correcting for gaps in the sequence. Only the three most abundant transposable elements are shown.
Figure 2
Figure 2
Map of chromosome 7 showing relative locations of genetic markers and other features. Recombination rate between markers is expressed as centiMorgans per 100 kb. The locations of blocks of conserved synteny, recombination rate, TE clusters, and restriction fragment length polymorphism markers are shown.
Figure 3
Figure 3
Correlation between TE content and recombination rate. Nine intervals on chromosome 7 were defined using 10 genetic markers. The Spearman rank correlation coefficient (Rs = 0.78) was significant (P = 0.02) at the 95% confidence interval.

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