It has been speculated that DNA methylation could complement genetic variation, as a mode for transferring heritable information, to contribute to phenotypic variation. Indeed, DNA methylation states can be maintained faithfully over both mitotic and meiotic cell division. According to this view, any accumulated variations in the DNA methylome have the potential to be carried over generations. However, bona fide examples of transgenerational methylation changes leading to substantially altered plant behavior remain rare, with the majority of reported DNA methylome variations attributable to underlying genetic differences rather than being truly epigenetic. Thus, the nature of DNA methylation and its contribution to short-term and transgenerational stress adaptation remain enigmatic. Given the conflicting nature of past studies, Ganguly et al. (10.1104/pp.17.00744) sought to systematically investigate the potential for environmentally induced changes in the DNA methylome in Arabidopsis that could convey transgenerational stress memory. Using a slow-onset water deprivation treatment in Arabidopsis, the authors investigated the malleability of the DNA methylome to drought stress within a generation and under repeated drought stress over five successive generations. While drought-associated epi-alleles in the methylome were detected within a generation, they did not correlate with drought-responsive gene expression. Six traits were analyzed for transgenerational stress memory, and the descendants of drought-stressed lineages showed one case of memory in the form of increased seed dormancy, and that persisted one generation removed from stress. With respect to transgenerational drought stress, there were negligible conserved differentially methylated regions in drought-exposed lineages compared with unstressed lineages. Furthermore, the experience of repeated drought stress was not observed to influence transgenerational epi-allele accumulation. These findings demonstrate that, while transgenerational memory is observed in one of six traits examined, they are not associated with causative changes in the DNA methylome, which appears to be relatively unaffected by drought stress.
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