Orateur
Description
The transition from seed to seedling involves major changes in nuclear organization and gene expression. However, the extent to which this developmental transition requires chromatin reprogramming - particularly changes in the histone variant repertoire - remains largely unexplored.
To dissect the molecular mechanisms that drive these chromatin reprogramming events we are combining chromatin conformation capture methods, microscopy imaging coupled with deep-learning-driven analysis tools, genetics, and epigenomics. I will present recent evidence that, in dry seeds, a specific histone H2B variant termed H2B.8 contributes to higher-order chromatin organization by forming spatial clusters that structure the 3D nuclear space. In dry seed embryos, the H2B.8 variant forms heterotypic nucleosomes at euchromatic transposons and lowly expressed genes and, during imbibition, modulates the transcriptional activation of a subset of these genes. We found that imbibition triggers a decrease in H2B.8 transcripts and the eviction of H2B.8 proteins in a process that operates independently of DNA replication. The observed histone eviction is not limited to H2B.8 as imbibition also induces the turnover of the H3.3 histone variant, thereby initiating a broad, replication-independent chromatin reprogramming process.
Our findings highlight a fundamental mechanism of epigenetic regulation during early plant development.