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Comparative genomics reveals the role of transposable elements in the evolution of pathogenicity in fungal pathogens of conifers

Tuan Duong: Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria

<div><em>Leptographium wageneri</em> is the causal agent of black stain root disease of conifers. Unlike the majority of other <em>Leptographium</em> spp., this species is a primary pathogen. Three varieties of <em>L. wageneri</em> can be distinguished based on optimal growth temperature in culture, the tree hosts that they infect and isozyme profiles. Nothing is known regarding the genetic determinants of pathogenicity in <em>L. wagneri</em>. To considser this question, we sequenced, annotated and compared the genomes of the three varieties of <em>L. wageneri</em> and the closely related non-pathogenic, <em>L. douglasii</em>. Available genomes of related species, including that of the bark-beetle associated and mildly pathogenic blue-stain fungus <em>Grosmannia clavigera </em>were also included in the analyses. The results showed that all three varieties of <em>L. wageneri</em> had larger genome sizes than the non-pathogenic species. This was as a consequence of the invasion and expansion of transposable elements (TEs). Interestingly, TE invasion has also occurred in <em>G. clavigera</em>, but to a lesser extent than has occurred in <em>L. wageneri</em>. Although gene catalogues were similar between the pathogenic and non-pathogenic species, genes encoding for small secreted proteins were highly diverse in the pathogens. These genes were found to reside in the TE-rich regions of the genomes. Overall, this study highlights the roles of TEs and TE-assisted evolution in the evolution of pathogenicity in the three varieties of <em>L. wageneri</em> and <em>G. clavigera</em>.</div>