Project description:This research uses consecutive generations of two independent mutation accumulation (MA) lines in model organism A. thaliana to understand transgenerational stability of epialleles via self-fertilization. With whole-genome bisulfite sequencing, regions of instability were identified and quantified. The vast majority of the methylated genome is stably inherited to offspring and the identified unstable regions do not change frequently between generations. Additionally, an epigenetic cross of two MA lines was created to understand inheritance patterns of epialleles via outcrossing in the absence of genetic variation. Whole-genome bisulfite sequencing was used to predict epigenotype of the offspring without single nucleotide polymorphisms. In regions of differential methylation between the parents, about half of regions show predictable inheritance.
Project description:Maintenance of CG methylation (mCG) patterns is essential for chromatin-mediated epigenetic regulation of transcription in plants and mammals. Using successive generations of an Arabidopsis thaliana mutant deficient in maintaining mCG, we found that mCG loss triggered genome-wide activation of alternative epigenetic mechanisms. However, these mechanisms involving RNA-directed DNA methylation, inhibiting expression of DNA demethylases, and retargeting of histone H3K9 methylation act in a stochastic and uncoordinated fashion. As a result, new and aberrant epigenetic patterns were progressively formed over several plant generations in the absence of mCG. Interestingly, the unconventional redistribution of epigenetic marks was necessary to ‘rescue’ the loss of mCG, since mutant plants impaired in rescue activities were severely dwarfed and sterile. Our results provide evidence that mCG is a central coordinator of epigenetic memory that secures stable transgenerational inheritance in plants. Keywords: DNA methylation profiling, epigenetic inheritance, mCIP, H3K9 methylation, RdDM, demethylase expression
Project description:DNA methylation at cytosine residues is an essential event for the normal development of multicellular eukaryotes. In mammals, de novo DNA methylation is restored to normal levels by the time of implantation, while epigenetic states of plant genes are often inherited over generations. Keywords: Organ comparison in methylome and transcriptome
Project description:DNA methylation in the promoters of plant genes sometimes leads to transcriptional repression, and the wholesale removal of DNA methylation as seen in methyltransferase mutants results in drastic changes in gene expression and severe developmental defects. However, many cases of naturally-occurring DNA methylation variations have been reported, whereby the altered expression of differentially methylated genes is responsible for agronomically important traits. The ability to manipulate plant methylomes to generate populations of epigenetically distinct individuals could provide invaluable resources for breeding and research purposes. Here we describe “epimutagenesis”, a novel method to rapidly generate variation of DNA methylation through random demethylation of the Arabidopsis thaliana genome. This method involves the expression of a human Ten-eleven translocation (TET) enzyme, and results in widespread hypomethylation that can be inherited to subsequent generations, mimicking mutants in the maintenance DNA methyltransferase met1. Application of TET-mediated epimutagenesis to agriculturally significant plants may result in differential expression of alleles normally silenced by DNA methylation, uncovering previously hidden phenotypic variations.
Project description:Eukaryotic genomes must maintain stable inheritance of epigenetic states. In plants, DNA methylation patterns are faithfully inherited over many generations but it is unknown how the dynamic activities of cytosine DNA methyltransferases and 5-methylcytosine DNA glycosylases, which remove 5-methylcytosine by base excision repair, interact to maintain epigenetic homeostasis. Here we show that a methylation-sensing gene regulatory circuit centered on a 5-methylcytosine DNA glycosylase gene is required for long-term epigenetic fidelity in Arabidopsis. Disrupting this circuit causes widespread methylation losses and abnormal phenotypes that progressively worsen over generations. In heterochromatin, these losses are counteracted such that methylation returns to a normal level over four generations. However, thousands of loci in euchromatin progressively lose DNA methylation between generations and remain unmethylated. We conclude that actively maintained equilibrium between methylation and demethylation activities is required to ensure long-term stable inheritance of epigenetic information.
Project description:The notion that genes are the sole units of heredity and that a barrier exists between soma and germline has been a major hurdle in elucidating the heritability of traits that were observed to follow a non-Mendelian inheritance pattern. It was only after the conception of “epigenetics” by C. H. Waddington that the effect of parental environment on subsequent generations via non-DNA sequence-based mechanisms, such as DNA methylation, chromatin modifications, non-coding RNAs and proteins, could be established in various organisms, now referred to as multigenerational epigenetic inheritance. Despite the growing body of evidence, the male gamete-derived epigenetic factors that mediate the transmission of such phenotypes are seldom explored, particularly in the model organism Drosophila melanogaster. Using the heat stress-induced multigenerational epigenetic inheritance paradigm in a widely used position-effect variegation line of Drosophila, named white-mottled, we have dissected the effect of heat stress on the sperm proteome in the current study. We demonstrate that multiple successive generations of heat stress at the early embryonic stage results in a significant downregulation of proteins associated with translation, chromatin organization, microtubule-based processes, and generation of metabolites and energy in the Drosophila sperms. Based on our findings, we propose chromatin-based epigenetic mechanisms, a well-established mechanism for environmentally induced multigenerational effects, as a plausible way of transmitting heat stress memory via the male germ line in subsequent generations. Moreover, we demonstrate the effect of multiple generations of heat stress on the reproductive fitness of Drosophila, shedding light on the adaptive or maladaptive potential of heat stress-induced multigenerational phenotypes.
Project description:Natural epigenetic variation provides a source for the generation of phenotypic diversity, but to understand its contribution to phenotypic diversity, its interaction with genetic variation requires further investigation. Here, we report population-wide DNA sequencing of genomes, transcriptomes, and methylomes of wild Arabidopsis thaliana accessions. Single cytosine methylation polymorphisms are unlinked to genotype. However, the rate of linkage disequilibrium decay amongst differentially methylated regions targeted by RNA-directed DNA methylation is similar to the rate for single nucleotide polymorphisms. Association analyses of these RNA-directed DNA methylation regions with genetic variants identified 2,372 methylQTL, which revealed the first population estimate of genetically dependent methylation variation. Analysis of invariably methylated transposons and genes across this population indicates that loci targeted by RNA-directed DNA methylation are epigenetically reactivated during male gametogenesis, which facilitates their silencing across generations.
Project description:Previous studies have shown that exposure to ionising radiation (IR) results in DNA methylation changes in plants. However, to the best of our knowledge, this phenomenon is yet to be studied across multiple generations. Furthermore, the exact role of these changes in the IR-induced plant response is still far from understood. Here, we study the effect of gamma radiation on DNA methylation and its effect across generations in young Arabidopsis plant. A multigenerational set-up was used in which three generations of seven-day old Arabidopsis thaliana plants were exposed to either of the different radiation treatments (30 mGy h-1, 60 mGy h-1, 110 mGy h-1, or 430 mGy h-1) or to natural background radiation (control condition) for 14 days. The parental generation consisted of previously non-exposed plants, whereas generation 1 and generation 2 plants had already received a similar irradiation in the previous one or two generations, respectively. Directly after exposure the entire methylomes were analysed with UPLC-MS to measure whole genome methylation levels. Whole genome bisulphite sequencing (WGBS) was used to identify differentially methylated regions (DMRs), including their methylation context in the three generations in three different radiation conditions (control, 30 mGy/h, and 110 mGy/h). Both intra- and intergenerational comparisons of the genes and transposable elements (TEs) associated with the DMRs were made across the gamma radiation exposure conditions. It was apparent that there was a higher number of changes in CpG methylation, whereas only limited changes in CHG methylation occurred and no changes in CHH methylation were observed. A clear increase in IR-induced DMRs was seen over the three generations that were exposed to the lowest dose rate, where Gen 2 had a markedly higher number of DMRs than the previous two generations (Parent and Gen 1). Counterintuitively, we did not see significant differences in the plants exposed to the higher dose rate. In addition, a large number of DMRs associated with TEs were found, the majority of them being hyper methylated, likely leading to more genetic stability. Next to that, a significant number of DMRs were associated with genes (either in their promoter associated region or gene body). A functional analysis of these genes (not included in with this data) showed an enrichment for genes related to development as well as various stress responses, including DNA repair, RNA splicing, and (a)biotic stress responses. These observations indicate a role of DNA methylation in the regulation of these genes in response to IR exposure and shows a possible role for epigenetics in adaptation to IR in plants.
Project description:DNA methylation is essential for silencing transposable elements and some genes in higher eukaryotes, implying that this modification must be tightly controlled. However, accidental changes in DNA methylation can be transmitted through mitosis, as in cancer, or meiosis, leading to epiallelic variation. Here, we demonstrate the existence of an efficient and faithful mechanism that protects against transgenerational loss of DNA methylation in the plant Arabidopsis. This process is specific to the subset of heavily methylated genomic repeats that are targeted by the RNAi machinery, and does not spread into flanking regions. Remethylation is often progressive over two to four sexual generations. This differential and incremental correction of epigenetic defects may preserve genome stability while increasing adaptive opportunities.