Department of Biological Sciences, Tokyo Metropolitan University, Minami-osawa 1-1, Hachioji, Tokyo, Japan.
Kihara Institute for Biological Research, Yokohama City University, Maioka 641-12, Totsuka, Yokohama, Kanagawa, Japan.
Plant Cell Physiol. 2019 Aug 1;60(8):1656-1665. doi: 10.1093/pcp/pcz077.
Karyogamy is a prerequisite event for plant embryogenesis, in which dynamic changes in nuclear architecture and the establishment of appropriate gene expression patterns must occur. However, the precise role of the male and female gametes in the progression of karyogamy still remains elusive. Here, we show that the sperm cell possesses the unique property to drive steady and swift nuclear fusion. When we fertilized egg cells with sperm cells in vitro, the immediate fusion of the male and female nuclei in the zygote progressed. This rapid nuclear fusion did not occur when two egg cells were artificially fused. However, the nuclear fusion of two egg nuclei could be accelerated by additional sperm entry or the exogenous application of calcium, suggesting that possible increase of cytosolic Ca2+ level via sperm entry into the egg cell efficiently can facilitate karyogamy. In contrast to zygotes, the egg-egg fusion cells failed to proliferate beyond an early developmental stage. Our transcriptional analyses also revealed the rapid activation of zygotic genes in zygotes, whereas there was no expression in fused cells without the male contribution. Thus, the male sperm cell has the ability to cause immediate karyogamy and to establish appropriate gene expression patterns in the zygote.
核融合是植物胚胎发生的前提事件，在此过程中必须发生核结构的动态变化和适当的基因表达模式的建立。然而，雄性和雌性配子在核融合进程中的确切作用仍然难以捉摸。在这里，我们表明精子细胞具有驱动稳定和快速核融合的独特性质。当我们在体外用精子细胞受精时，受精卵中雄性和雌性核的立即融合会发生。当两个卵母细胞被人工融合时，这种快速核融合不会发生。然而，通过额外的精子进入或外源应用钙，可以加速两个卵核的核融合，这表明通过精子进入卵母细胞可能增加细胞溶质 Ca2+水平可以有效地促进核融合。与受精卵相反，卵-卵融合细胞不能在早期发育阶段后增殖。我们的转录分析还揭示了受精卵中合子基因的快速激活，而在没有雄性贡献的融合细胞中则没有表达。因此，雄性精子细胞具有立即进行核融合并在受精卵中建立适当基因表达模式的能力。
