Zygotic Resetting of the HISTONE 3 Variant Repertoire Participates in Epigenetic Reprogramming in Arabidopsis

In most eukaryotes, the HISTONE 3 family comprises several variants distinguished by their amino acid sequence, localization, and correlation with transcriptional activity [1-3]. Transgenerational inheritance of epigenetic information carried by histones is still unclear [4, 5]. In addition to covalent histone modifications, the mosaic distribution of H3 variants onto chromatin has been proposed to provide a new level of epigenetic information [6]. To study the transmission of patterns of H3 variants through generations, we combined transcriptional profiling and live imaging of the 13 H3 variants encoded by the Arabidopsis plant genome [7]. In comparison with somatic cells, only a restricted number of H3 variants are present in male and female gametes. Upon fertilization, H3 variants contributed by both gametes are actively removed from the zygote chromatin. The somatic H3 composition is restored in the embryo by de novo synthesis of H3 variants. A survey of Arabidopsis homologs of animal H3 chaperones suggests that removal of parental H3 from the zygote nucleus relies on a new mechanism. Our results suggest that reprogramming of parental genomes in the zygote limits the inheritance of epigenetic information carried by H3 variants across generations.