A great portion of organism genomes are composed of “junk” DNA that their cells must stop from transcribing. This “junk” DNA is composed of transposable elements (TEs), which will generate mutations if allowed to express. However, each cell does not need to determine de novo what regions of the genome are TEs, rather this information is passed down from a progenitor cell in a process termed epigenetic inheritance. In both plants and animals, epigenetic inheritance occurs across mitotic cell divisions and, at least in plants, it also occurs across meiotic divisions and fertilization. Plant gametophytes and embryo are the battleground for the evolutionary arms race between TE activity and host-cell suppression of TEs. The protection of the germ cells and the very young embryo of the progeny are key steps of genome integrity that require trans-generational epigenetic suppression of TEs. The conceptual base of this project is that TE derived siRNAs accumulating in the pollen sperm cells (SCs) are part of a trans-generational genome safeguard mechanism that protects TE expression and transposition in the SCs and after fertilization in the embryo. This project will specifically investigate:Aim 1)The movement of pollen TE easiRNAs to the SCs, embryo and the endosperm.Aim 2)The role of TE easiRNAs in initiation of a siRNA amplification step in the embryo.Aim 3)The role of TE easiRNAs in the protection of the embryo’s genome from the transposition of female active TEs in the endosperm or/and the embryo.Aim 4)The role of TE SC siRNAs in imprinted embryo gene regulation.In order to achieve these aims, this project will make use of several molecular and cellular biology techniques. This will enhance the knowledge of the transgenerational epigenetic regulation of plant genomes, and the results will impact the fields of epigenetics, RNA silencing, sRNA transport and others, and their applications in plant breeding and production and human healt.