Project description:Changes in genome structure and gene expression have been documented in both resynthesized and natural allopolyploids that contain two or more divergent genomes. The underlying mechanisms for rapid and stochastic changes in gene expression are unknown. Arabidopsis suecica is a natural allotetraploid derived from the extant species A. thaliana and A. arenosa. Here we report that reduced DNA methylation in met1-RNAi A. suecica lines altered the expression of ~200 genes encoding transposons, centromeric and heterochromatic RNAs, and predicted proteins. Reduced DNA methylation occurred frequently in promoter regions of the upregulated genes but not of the repressed genes and led to increased mobility of En/Spm-like transposons in met1-RNAi A. suecica lines. Compared to A. arenosa centromeres, A. thaliana centromeres were hypermethylated, which correlates with higher levels of small RNA accumulation in A. thaliana centromeres than that in A. arenosa centromeres. Derepression of the genes examined was primarily derived from A. thaliana subgenome, and A. arenosa genes are less affected by methylation defects. Moreover, non-CG (CC) methylation in the promoter region of A. thaliana At2g23810 was maintained in resynthesized allotetraploids, and the methylation spread within the promoter region in natural A. suecica, leading to silencing of At2g23810, which was demethylated and reactivated in met1-RNAi A. suecica lines. We suggest that a subset of A. thaliana and A. arenosa genes are differentially methylated in natural allopolyploids, and some A. thaliana genes including centromeres are subjected to transcriptional repression and genome-specific RNA-mediated DNA methylation in Arabidopsis allopolyploids. Keywords: gene expression in reduced DNA methylation lines in Arabidopsis allotetraploids
Project description:Stress priming is a critical adaptive mechanism that enables plants to enhance responses to recurring environmental stresses. While transcriptomic changes associated with cold stress priming have been reported, the underlying epigenetic mechanisms remain largely unknown. In this study, we investigated transcriptomic and DNA methylation dynamics in cold-primed and non-primed Arabidopsis thaliana plants. Cold stress induces distinct gene expression patterns between primed and non-primed plants, accompanied by DNA methylation changes across all cytosine contexts in both protein-coding genes and transposable elements (TEs). Notably, CHH methylation within gene bodies and TEs is markedly reduced in cold-primed plants, suggesting a role for DNA hypomethylation in establishing cold stress memory. This hypomethylation correlates with decreased expression of the CMT2 DNA methyltransferase and components of the RNA-directed DNA methylation (RdDM) pathway, indicating a passive demethylation process during cold treatment. Furthermore, DNA methylation mutants exhibit enhanced cold stress memory, highlighting the role of methylation in preventing spurious gene activation and maintaining priming specificity. Particularly, met1, deficient in CG methylation, shows reduced methylation at the CBF gene cluster, correlating with their overexpression and enhanced activation of downstream cold-responsive genes. Our findings show that DNA methylation modulates cold stress memory by shaping chromatin and ensuring transcriptional precision.