Epigenetic modifications can provide information about the connection between genotype and phenotype and which can be directly affected by environmental conditions. In temperate perennial fruit species like sweet cherry, prolonged exposition to cold temperatures is required for dormancy release and flowering in spring. Besides genetic diversity, epigenetic regulation is believed to contribute to different chilling requirements and phenotypic plasticity among cultivars. We set out to profile methylation patterns of floral buds from sweet cherry cultivars contrasting in chilling requirement. We performed a sequence-based genome-wide differential methylation analysis using whole genome sequencing of bisulfite-treated DNA of a high chill cultivar ('Kordia': 1637 CH for budbreak) at four time points of cold accumulation during dormancy. As a result, we obtained global methylation levels and methylation-demethylation patterns at 0, 443, 1295 and 1637 CH. A total of 50% of the reads mapped uniquely to the reference genome of 'Kordia' (untreated genome). Approximately a 25-30% of total cytosines were methylated in all the conditions, corresponding to a 10-12, 9-10 and 7-8% of specific methylations at the CpG, CHG and CHH sites, respectively. Annotation of differentially methylated regions (DMRs) is under development, focusing on the distinctive patterns of transposon and gene body methylation, in an attempt to describe epigenetic marks that may be contributing to contrasting chilling requirement.
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