Transposons, RNA Interference and Heterochromatin



 DESCRIPTION (provided by applicant): The germlines of plants and animals undergo genome reprogramming in order to reset epigenetic marks that would otherwise interfere with pluripotency of the zygote. Perhaps chief among these marks are epigenetic modifications of transposable elements (TE), which make up a majority of most eukaryotic genomes. We have found that small interfering RNA derived from heterochromatin plays a key role in germline reprogramming in plants, and there is mounting evidence for a similar phenomenon in animals. Germ cells in plants differentiate from the products of meiosis by mitotic division, along with companion cells that resemble nurse cells and other support cells in animals. We have found that reprogramming of the pollen grain companion cell nucleus (the vegetative nucleus or VN) results in transposon activation, and that a new class of "epigenetically activated" small interfering RNA (easiRNA) accumulate in sperm cells, that have the potential to silence these same transposons. We have recently found that genome reprogramming depends on DNA methylation, but also on the deposition and modification of specific histone variants, that is likey the result of cell cycle dependent chromatin remodeling. Epigenetic inheritance is far more widespread in plants than in mammals, although the mechanisms are largely conserved, so that plants provide an excellent system to study their origin. We will investigate the mechanism of germline reprogramming in plants, and the transgenerational consequences when reprogramming goes awry.