Lay summary
The plant genome harbors an extraordinary plasticity: fully differentiated plant cells can be re-programmed to produce new individuals either sexually (via the production of gametes in flower organs) or clonally (via the production of clonal sprouts from vegetative tissues). This is in stark contrast to animals that must set aside a lineage of undifferentiated cells for reproduction (germ cells) and cannot naturally regenerate from body parts. Recent studies suggest that plant ge-nome plasticity may be supported by specific chromatin organization and composition. But the precise events and control mechanisms of large-scale chromatin remodeling and chromosome organization in reprogramming processes, as described above, are barely explored. The aim of this research proposal is three-fold:(a) Sexual reproduction in plants involves double fertilization. The two female gametes are clonally derived in a multicellular structure but have distinct post-fertilization fates. We hypothesize that distinct epigenetic chromatin signatures are established early during gametogenesis to mark their cell fate. *We will seek for gametic chromatin signatures and analyze their role in gametic fate.*(b) Reproductive success relies on the endosperm, an extra-embryonic nurse tissue produced at fertilization. The dosage of paternally vs maternally-derived products is crucial for its development; alteration can result in seed abortion and hybridization failure. We discovered a specific heterochromatin fraction which responds to ploidy alterations in a parent-of-origin-dependent manner. *We will investigate the role, control, and nature of endosperm-specific heterochromatin in parental dosage regulation and the hybridization barrier.*(c) During clonal propagation, somatic cells de-differentiate under appropriate stimuli and become totipotent. Progeny is produced via somatic embryogenesis or organogenesis. We hypothesize that this genome-wide reprogramming involves specific large-scale chromatin modifica-tions. *We will describe the chromatin dynamics accompanying reprogramming in an experimental case of clonal propagation.*