Meyer Stephanie, Scholten Stefan
Developmental Biology and Biotechnology, Biocenter Klein Flottbek, University of Hamburg, Ohnhorststrasse 18, 22609 Hamburg, Germany.
Curr Biol. 2007 Oct 9;17(19):1686-91. doi: 10.1016/j.cub.2007.08.046. Epub 2007 Sep 13.
Hybrid vigor or heterosis results from the combination of genetically distant genomes at fertilization, and as well as being of major commercial importance, it is held to contribute significantly to fitness [1]. Activation of the paternal genome marks the transition from maternal to zygotic control of development, but a reported delay of paternal-genome activation in flowering plants [2-4] and animals [5, 6] excludes heterosis from impacting on very early development. We have analyzed the allele-specific expression of 25 genes after fertilization of the egg in maize and show immediate equivalent parental genomic contribution to the zygote. Every gene expressed before the first cell division of the zygotes showed paternal transcripts. Sequence comparisons indicate that these genes are involved in a range of processes and are distributed throughout the genome. Our findings confirm that some plant species have evolved a strategy to activate the paternal genome immediately after fertilization, in contrast to the situation in other plants and in animals. Such an extensive activation of the paternal genome very early in development is consonant with observations of high levels of heterosis in early hybrid maize embryos [7, 8], indicating a significant impact of this sexual strategy on fitness.
杂种优势或杂交活力源于受精时遗传距离较远的基因组的组合，它不仅具有重要的商业价值，还被认为对适应性有显著贡献[1]。父本基因组的激活标志着从母体对发育的控制向合子控制的转变，但有报道称开花植物[2-4]和动物[5, 6]中父本基因组激活存在延迟，这使得杂种优势无法影响非常早期的发育。我们分析了玉米卵细胞受精后25个基因的等位基因特异性表达，结果表明父本基因组对合子的贡献在受精后立即与母本相当。在合子第一次细胞分裂之前表达的每个基因都显示有父本转录本。序列比较表明，这些基因参与一系列过程，且分布于整个基因组。我们的研究结果证实，与其他植物和动物的情况不同，一些植物物种已经进化出一种在受精后立即激活父本基因组的策略。在发育早期对父本基因组如此广泛的激活与早期杂交玉米胚中高水平杂种优势的观察结果一致[7, 8]，表明这种有性策略对适应性有重大影响。
