Epigenetic regulation of repetitive DNA through mitotic asynchrony following double fertilization in angiosperms

Several recent studies show that companion cells in flowering plant gametophytes relax epigenetic control of transposable elements (TEs) to promote production of small RNA that presumably assist nearby reproductive cells in management of TEs. In light of this possibility, a closer look at the timing of cell division in relation to angiosperm double fertilization is warranted. From such an analysis, it is conceivable that double fertilization can drive angiosperm evolution by facilitating crosses between genetically diverse parents. A key feature of this ability is the order of cell division following double fertilization, since division of the primary endosperm nucleus prior to the zygote would produce small RNA capable of identifying TEs and defining chromatin states in the zygote prior to its entry into S-phase of the cell cycle. Consequently, crosses leading to increased ploidy or between genetically diverse parents would yield offspring better capable of managing a diverse complement of TEs and repetitive DNA. Considering double fertilization in this regard challenges previous notions that the primary purpose of endosperm is for improved seed reserve storage and utilization.