Mobilization of transposons by a mutation abolishing full DNA methylation in Arabidopsis

Abstract

A major component of the large genomes of higher plants and vertebrates comprises transposable elements and their derivatives, which potentially reduce the stability of the genome. It has been proposed that methylation of cytosine residues may suppress transposition, but experimental evidence for this has been limited. Reduced methylation of repeat sequences results from mutations in the Arabidopsis gene DDM1 (decrease in DNA methylation), which encodes a protein similar to the chromatin-remodelling factor SWI2/SNF2 (ref. 7). In the ddm1-induced hypomethylation background, silent repeat sequences are often reactivated transcriptionally, but no transposition of endogenous elements has been observed. A striking feature of the ddm1 mutation is that it induces developmental abnormalities by causing heritable changes in other loci. Here we report that one of the ddm1-induced abnormalities is caused by insertion of CAC1, an endogenous CACTA family transposon. This class of Arabidopsis elements transposes and increases in copy number at high frequencies specifically in the ddm1 hypomethylation background. Thus the DDM1 gene not only epigenetically ensures proper gene expression, but also stabilizes transposon behaviour, possibly through chromatin remodelling or DNA methylation.

Host genome surveillance for retrotransposons by transposon-derived proteins

“…As Abp1 and Cbh1 can bind to distinct loci, and that these factors do not always colocalize with SHREC 23 , CENP-B binding in contexts other than heterochromatin and transposable elements might recruit activities important for other chromatin transactions, such as transcription and DNA replication. Accumulating evidence implicates transposable-element-derived sequences as regulators of gene expression in diverse species 1, [35][36][37] . A substantial fraction of human promoters contains transposable element sequences 38 , and instances of their contribution to gene regulation have been documented 1, 39 .…”

Genome-wide comparative analysis of the transposable elements in the related species Arabidopsis thaliana and Brassica oleracea

“…Prior studies of TEs in A. thaliana identified four families of CACTA-like elements (named Atenspm1-4), of which one (Atenspm1) was shown to be transpositionally active (31,32). Comparison of the transposases of Atenspm1 (889 aa) with a CACTA-like element (703 aa) isolated from another brassica species, Brassica rapa (33), served to identify the most conserved region as a 100-aa segment (77% identical) corresponding to positions 272-371 in Atenspm1.…”

Homology-dependent methylation in primate repetitive DNA

“…The immediate inactivation of methylated sequences in N. crassa is a result of massive C-to-T mutational events due to the deamination of methylated cytosines into thymines, which is likely to be induced by the methylase itself (5, 6). Another example indicating that DNA methylation controls the potential deleterious effects of TEs comes from plants: Only TEs exhibit high methylation levels, which prevents their expression (7,8). In mammals, several lines of experimental and theoretical evidence suggest the existence of a specific methylation pattern in TEs (9-14).…”