GH1-HMGA proteins restrict RNA-directed DNA methylation and antagonize linker histone H1 at euchromatic transposable elements
Year: 2026
Type: preprint
Abstract: In plant genomes, transposable elements (TEs) are silenced by CG and non-CG DNA methylation, with non-CG methylation maintained by CMT chromomethylases and the RNA-directed DNA methylation (RdDM) pathway. In Arabidopsis, linker histone H1 differentially influences these pathways, as loss of H1 causes non-CG hypermethylation at pericentromeric TEs but hypomethylation at euchromatic TEs in gene-rich regions. The molecular basis of this antagonism has remained unclear. Here, we show that GH1-HMGAs, a family of H1-related High Mobility Group proteins, bind AT-rich sequences at euchromatic TEs and prevent RdDM-dependent non-CG methylation by limiting siRNA accumulation. Furthermore, GH1-HMGA and H1 compete for chromatin association at these TEs, as loss of GH1-HMGA triggers ectopic H1 redistribution, while loss of H1 increases GH1-HMGA enrichment, providing a mechanistic explanation for the non-CG hypomethylation observed in h1 mutants. Collectively, these findings reveal how GH1-HMGA proteins specifically restrain RdDM activity at euchromatic TEs and elucidate how the H1/GH1-HMGA balance spatially partitions distinct DNA methylation pathways across the genome.
Institutions: Centre National de la Recherche Scientifique, Inserm, Université Clermont Auvergne, Institut Génétique, Reproduction et Développement, Université Paris-Saclay, Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement, Institut des Sciences des Plantes de Paris Saclay, Sorbonne Université, Développement Adaptation et Vieillissement, Gregor Mendel Institute of Molecular Plant Biology, Austrian Academy of Sciences, Vienna Biocenter
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7212303489