Johannes lab: Two companion papers about spontaneous epimutations are out in Genome Biology. We show, for the first time, that stochastic methylation changes act as an aging clock in trees.
AlphaBeta: computational inference of epimutation rates and spectra from high-throughput DNA methylation data in plants.
Yadollah Shahryary, Aikaterini Symeonidi, Rashmi R. Hazarika, Johanna Denkena, Talha Mubeen, Brigitte Hofmeister, Thomas van Gurp, Maria Colomé-Tatché, Koen J.F. Verhoeven, Gerald Tuskan, Robert J. Schmitz, and Frank Johannes (2020).
Stochastic changes in DNA methylation (i.e., spontaneous epimutations) contribute to methylome diversity in plants. Here, we describe AlphaBeta, a computational method for estimating the precise rate of such stochastic events using pedigree-based DNA methylation data as input. We demonstrate how AlphaBeta can be employed to study transgenerationally heritable epimutations in clonal or sexually derived mutation accumulation lines, as well as somatic epimutations in long-lived perennials. Application of our method to published and new data reveals that spontaneous epimutations accumulate neutrally at the genome-wide scale, originate mainly during somatic development and that they can be used as a molecular clock for age-dating trees.
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A genome assembly and the somatic genetic and epigenetic mutation rate in a wild long-lived perennial Populus trichocarpa.
Brigitte T. Hofmeister, Johanna Denkena, Maria Colomé-Tatché, Yadollah Shahryary, Rashmi Hazarika, Jane Grimwood, Sujan Mamidi, Jerry Jenkins, Paul P. Grabowski, Avinash Sreedasyam, Shengqiang Shu, Kerrie Barry, Kathleen Lail, Catherine Adam, Anna Lipzen, Rotem Sorek, Dave Kudrna, Jayson Talag, Rod Wing, David W. Hall, Daniel Jacobsen, Gerald A. Tuskan, Jeremy Schmutz, Frank Johannes, and Robert J. Schmitz (2020).
Background: Plants can transmit somatic mutations and epimutations to offspring, which in turn can affect fitness. Knowledge of the rate at which these variations arise is necessary to understand how plant development contributes to local adaption in an ecoevolutionary context, particularly in long-lived perennials.
Results: Here, we generate a new high-quality reference genome from the oldest branch of a wild Populus trichocarpa tree with two dominant stems which have been evolving independently for 330 years. By sampling multiple, age-estimated branches of this tree, we use a multi-omics approach to quantify age-related somatic changes at the genetic, epigenetic, and transcriptional level. We show that the per-year somatic mutation and epimutation rates are lower than in annuals and that transcriptional variation is mainly independent of age divergence and cytosine methylation. Furthermore, a detailed analysis of the somatic epimutation spectrum indicates that transgenerationally heritable epimutations originate mainly from DNA methylation maintenance errors during mitotic rather than during meiotic cell divisions.
Conclusion: Taken together, our study provides unprecedented insights into the origin of nucleotide and functional variation in a long-lived perennial plant.
