Schattner Saskia, Schattner Jan, Munder Fabian, Höppe Eva, Walter Wilhelm J
Department of Biology, Institute for Plant Science and Microbiology, University of Hamburg, Hamburg, Germany.
Department Medicine, Health and Medical University Potsdam, Potsdam, Germany.
Front Plant Sci. 2021 Feb 16;11:601282. doi: 10.3389/fpls.2020.601282. eCollection 2020.
Upon pollination, two sperm cells are transported inside the growing pollen tube toward the apex. One sperm cell fertilizes the egg cell to form the zygote, while the other fuses with the two polar nuclei to form the triploid endosperm. In Arabidopsis thaliana, the transport of the two sperm cells is characterized by sequential forward and backward movements with intermediate pauses. Until now, it is under debate which components of the plant cytoskeleton govern this mechanism. The sperm cells are interconnected and linked to the vegetative nucleus via a cytoplasmic projection, thus forming the male germ unit. This led to the common hypothesis that the vegetative nucleus is actively transported via myosin motors along actin cables while pulling along the sperm cells as passive cargo. In this study, however, we show that upon occasional germ unit disassembly, the sperm cells are transported independently and still follow the same bidirectional movement pattern. Moreover, we found that the net movement of sperm cells results from a combination of both longer and faster runs toward the pollen tube apex. We propose that the observed saltatory movement can be explained by the function of kinesins with calponin homology domain (KCH). This subgroup of the kinesin-14 family actively links actin filaments and microtubules. Based on KCH's specific properties derived from experiments, we built a tug-of-war model that could reproduce the characteristic sperm cell movement in pollen tubes.
授粉后，两个精子细胞在生长的花粉管内朝着顶端运输。一个精子细胞使卵细胞受精形成合子，而另一个与两个极核融合形成三倍体胚乳。在拟南芥中，两个精子细胞的运输特点是有顺序的向前和向后运动，并伴有中间停顿。到目前为止，关于植物细胞骨架的哪些成分控制这一机制仍存在争议。精子细胞通过细胞质突起相互连接并与营养核相连，从而形成雄配子体。这导致了一个普遍的假设，即营养核通过肌球蛋白马达沿着肌动蛋白丝被主动运输，同时将精子细胞作为被动货物一起拉动。然而，在本研究中，我们表明，在偶尔的雄配子体解体时，精子细胞独立运输，并且仍然遵循相同的双向运动模式。此外，我们发现精子细胞的净运动是由朝着花粉管顶端更长、更快的移动共同作用的结果。我们提出，观察到的跳跃式运动可以用具有钙调蛋白同源结构域（KCH）的驱动蛋白的功能来解释。驱动蛋白-14家族的这个亚组积极地连接肌动蛋白丝和微管。基于从实验中得出的KCH的特定特性，我们构建了一个拔河模型，该模型可以重现花粉管中精子细胞的特征性运动。
