751 / 2019-05-16 00:17:09

Mobile DNA, epigenetics and rapid adaptation

Transposable elements, epiRILs, DNA methylation, Mutations, Chromatin, Adaptation

Epigenetic Regulation > Epigenetic Regulation

Transposable elements (TEs) are mobile DNA sequences that self-propagate and many eukaryotic genomes are laden with the remnants of once active TEs. Yet, the contribution of TE mobilization to the creation of heritable mutations is unclear. Using our population of A. thaliana epigenetic recombinant inbred lines, we found that following the transient release of epigenetic silencing, several TEs were mobilized. New TE insertions accumulated exponentially, thus leading rapidly -in just over a few generations- to high rates of heritable mutations. Moreover, most insertions occurred near or within genes and gene targets differed between TE families. Notably, we uncovered a key role for the histone variant H2A.Z in the integration of Ty1/copia retrotransposons preferentially within environmentally responsive genes and away from essential genes. Furthermore, the effects of newly inserted Ty1/copia copies on gene expression were often exacerbated or alleviated once these copies became epigenetically silenced, with major impacts on adaptive traits such as nectar production or flowering time.
Our findings demonstrate that thanks to the specific chromatin tropisms they exhibit, TEs are potent episodic (epi)mutagens that can dramatically increase the potential for rapid adaptation while limiting the mutational load. This new knowledge challenges our understanding of the evolutionary process by indicating that it may not be solely fueled by random mutations arising at a constant rate.