Molecular evolution of Histone variants

In the germline of animals, mobility of endogenous elements called transposons causes genomic instability that is transmitted to offspring. The mobility of transposons is prevented by pathways that are not conserved in plants. In a specific group of land plants, we identified that a variant of one of the main proteins that packages the genome provides a potential new mechanism in transposon silencing. Understanding chromatin function is central to comprehend the complexity of genome regulation in eukaryotes. The major component of chromatin are variants of the core histones, which wrap DNA into nucleosomes and control accessibility to the genome. This project aims to characterize the function of a newly identified domain of the core histone H2A. In H2A.H, this domain differs remarkably from other variants of histone H2A. H2A.H is present only in the male germline of liverworts. We propose to establish how the variant H2A.H evolved and to identify the properties it confers to chromatin and study its function in silencing transposons in the male germline. We will combine phylogenetic, and molecular biology to establish how the variant H2A.H was selected and how it acquired its specific expression in the male germline. Biochemical and genetic analysis will identify the pathway responsible for the enrichment of H2A.H in heterochromatin of male gametes and its involvement in repressing transposon in the germline. Beyond its interest in germline biology, this project will provide important insights in evolution of chromatin in eukaryotes and open potential avenues in synthetic strategies to engineer chromatin.