International Symposium on Cereal Leaf Blights 2019 | University College Dublin, Ireland | 22-24 May 2019

DNA methylation impacts genome evolution of Zymoseptoria tritici

Mareike Möller*
University of Kiel

Kathrin Happ
University of Kiel

Maja Stralucke
University of Kiel

Eva H. Stukenbrock
University of Kiel
Max Planck Institute for Evolutionary Biology

Oral Presentation
Evolution and Population Biology

Moore Auditorium, UCD O'Brien centre for Science
22 May 2019, 10:40

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Methylation of DNA is an important component of epigenetic regulation and found throughout all forms of life ranging from prokaryotes to mammals. However, the extent and function of DNA methylation differ between taxa. Previous studies in the plant pathogenic fungus Zymoseptoria tritici report absence of DNA methylation in the reference strain IPO323 due to amplification and inactivation of the DNA methyltransferase gene Ztdim2 by repeat-induced point mutations (RIP). In this study, we demonstrate that Ztdim2 ,however, is not inactivated in other strains of Z. tritici that have maintained a functional Ztdim2 gene. We used bisulfite sequencing to identify genome wide cytosine methylation levels in strains with and without a functional Ztdim2. The presence of a functional Ztdim2 correlates with high levels of cytosine methylation on transposable elements indicating a role in the genome defenses. We present evidence for the presence of small amounts of DNA methylation, even in strains containing an inactive Ztdim2 gene suggesting that DNA methylation was maintained over time. This scenario is supported by the presence of a putative maintenance DNA methyltransferase, Ztdnmt5 in the Z. tritici genome. Integration of a functional Ztdim2 variant in strains with inactivated Ztdim2 restores DNA methylation levels indicating de novo methylation activity of Ztdim2. We compared the genomes of strains that maintained high levels of DNA cytosine methylation with genomes of strains without Ztdim2 activity. We found that the presence of DNA methylation alters nucleotide composition by promoting C – T transversions and thereby likely contributes to transposon inactivation and influences genome evolution dynamics. Taken together, our results indicate that the presence of widespread DNA methylation is a variable trait in Z. tritici populations that impacts genome evolution as a mechanism of genome defense.