Transposons, RNA Interference and Heterochromatin

描述（由申请人提供）：植物和动物的种系经历基因组重编程，以重置表观遗传标记，否则这些标记会干扰受精卵的多能性。这些标记中最主要的可能是转座元件（TE）的表观遗传修饰，它构成了大多数真核生物基因组的大部分。我们发现源自异染色质的小干扰RNA在植物种系重编程中发挥着关键作用，并且越来越多的证据表明动物中也存在类似现象。植物中的生殖细胞源自有丝分裂的减数分裂产物，并且许多伴随细胞也像动物中的护士细胞和其他支持细胞一样分化。我们发现，花粉粒伴细胞核（营养核或 VN）的重编程会导致转座子激活，并且一类新的“表观遗传激活”小干扰 RNA (easiRNA) 在精子细胞中积聚。在胚珠中，同一小RNA途径中的突变体导致额外的减数分裂二倍体生殖细胞的分化，以及卵子中的TE激活。异常的生殖细胞规格对植物繁殖具有深远的影响，包括克隆未减数种子（无融合生殖）的生产。我们将研究植物种系重编程的机制，以及小RNA在生殖细胞身份规范中的功能。我们还将研究当重编程出错时表观等位基因的跨代遗传。我们有初步证据表明，系统移动的小RNA在配子中积累，并从配子传递到受精卵，从而提供了跨代遗传的机制。

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 arise from the products of meiosis by mitotic division, and a number of companion cells also differentiate resembling 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. In ovules, mutants in this same small RNA pathway result in differentiation of additional ameiotic diploid germ cells, as well as TE activation in the egg. Aberrant germ cell specification has profound implications for plant reproduction, including the production of clonal unreduced seeds (apomixis). We will investigate the mechanism of germline reprogramming in plants, and the function of small RNA in specification of germ cell identity. We will also investigate the transgenerational inheritance of epialleles when reprogramming goes awry. We have preliminary evidence that systemically mobile small RNA accumulate in the gametes, from which they are passed into the fertilized zygote, providing a mechanism for transgenerational inheritance.