Résumé
In the past years a plethora of roles for small RNAs (sRNAs) have been revealed in developmental biology, physiology, pathogen interactions, and more recently in genome stability and transposon control. sRNAs have a repressive impact on gene expression by directly interfering with endogenous mRNAs or virus RNA, or by maintaining heterochromatin. In plants, the most abundant sRNAs are by far the ones produced from heterochromatic loci and playing a role in epigenetic regulation. Here, I review some specific examples of the roles of these sRNAs belonging to the class of small interfering RNAs (siRNAs) in controlling the epigenetic regulation of the genome. I will highlight their role as mediators of epigenetic information at various organization levels: between two alleles within a single cell, two tissues within an organism, two individuals or two generations within a species, and even two species within a kingdom.