Fertilization-Coupled Sperm Nuclear Fusion Is Required for Normal Endosperm Nuclear Proliferation
Fertilization-Coupled Sperm Nuclear Fusion Is Required for Normal Endosperm Nuclear Proliferation
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DOI：
10.1093/pcp/pcz158
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发表时间：
2020-01-01
影响因子：
4.9
通讯作者：
Nishikawa, Shuh-ichi
中科院分区：
文献类型：
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作者：
Maruyama, Daisuke;Higashiyama, Tetsuya;Nishikawa, Shuh-ichi
被子植物表现出双重受精，这是一个从花粉管中释放出来的精子与卵子受精，另一个精子与中央细胞受精，分别产生胚胎和胚乳的过程。我们先前已经报道了拟南芥免疫球蛋白结合蛋白(Bip)的两个极性核融合缺陷双敲除突变体，Bip是定位于内质网(ER)的热休克蛋白70(Hsp70)的分子伴侣(Bip1 Bip2)及其伙伴ER驻留J蛋白ERdj3A和P58(IPK)(erdj3a p58(IPK))。这些突变体在外核膜融合方面存在缺陷，与野生型花粉受精后表现出特有的种子发育缺陷，并伴随着胚乳核的异常增殖。在这项研究中，我们使用延时活细胞成像分析来确定这些突变种子的胚乳核分裂异常的原因。我们发现，在受精时，bip1、bip2或erdj3a p58(Ipk)双突变雌配子体的中央细胞也存在精子核融合缺陷。精子核融合是在第一次胚乳核分裂开始后实现的。然而，浓缩精子核的分裂导致胚乳核的异常分裂和父本衍生基因的延迟表达。而另一个双基因敲除突变体erdj3b p58(Ip)(K)在极核内膜融合中存在缺陷，但在受精时未表现出异常的胚乳核增殖。因此，我们认为有丝分裂前精子在中央细胞的核融合对正常胚乳的核增殖是至关重要的。
Angiosperms exhibit double fertilization, a process in which one of the sperm cells released from the pollen tube fertilizes the egg, while the other sperm cell fertilizes the central cell, giving rise to the embryo and endosperm, respectively. We have previously reported two polar nuclear fusion-defective double knockout mutants of Arabidopsis thaliana immunoglobulin binding protein (BiP), a molecular chaperone of the heat shock protein 70 (Hsp70) localized in the endoplasmic reticulum (ER), (bip1 bip2) and its partner ER-resident J-proteins, ERdj3A and P58(IPK) (erdj3a p58(ipk)). These mutants are defective in the fusion of outer nuclear membrane and exhibit characteristic seed developmental defects after fertilization with wild-type pollen, which are accompanied by aberrant endosperm nuclear proliferation. In this study, we used time-lapse live-cell imaging analysis to determine the cause of aberrant endosperm nuclear division in these mutant seeds. We found that the central cell of bip1 bip2 or erdj3a p58(ipk) double mutant female gametophytes was also defective in sperm nuclear fusion at fertilization. Sperm nuclear fusion was achieved after the onset of the first endosperm nuclear division. However, division of the condensed sperm nucleus resulted in aberrant endosperm nuclear divisions and delayed expression of paternally derived genes. By contrast, the other double knockout mutant, erdj3b p58(ip)(k), which is defective in the fusion of inner membrane of polar nuclei but does not show aberrant endosperm nuclear proliferation, was not defective in sperm nuclear fusion at fertilization. We thus propose that premitotic sperm nuclear fusion in the central cell is critical for normal endosperm nuclear proliferation.