F-Actin Mediated Focusing of Vesicles at the Cell Tip Is Essential for Polarized Growth
F-Actin Mediated Focusing of Vesicles at the Cell Tip Is Essential for Polarized Growth
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DOI：
10.1104/pp.17.00753
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发表时间：
2018-01-01
期刊：
影响因子：
7.4
通讯作者：
Vidali, Luis
中科院分区：
文献类型：
--
作者：
Bibeau, Jeffrey P.;Kingsley, James L.;Vidali, Luis
肌动蛋白已被证明是必不可少的尖端生长在一系列的植物模型，包括小立碗藓。一种假说是扩散可以运输分泌囊泡，而肌动蛋白在分泌过程中起调节作用。或者，它是可能的，肌动蛋白为基础的运输是必要的，以克服囊泡运输限制，以维持分泌。因此，扩散，分泌动力学和细胞几何形状的定量分析是必要的，以澄清肌动蛋白在极化生长中的作用。使用荧光恢复后的光漂白分析，我们首先表明，分泌囊泡移动和积累在尖端的肌动蛋白依赖的方式。然后，我们解聚F-肌动蛋白解耦囊泡扩散肌动蛋白介导的运输和测量的扩散系数和浓度的囊泡。使用这些值，我们构建了一个理论上的基于扩散的生长模型，表明具有足够快的囊泡融合动力学，扩散可以支持正常的细胞生长速率。我们进一步完善了我们的模型，以探索实验推断的囊泡融合动力学和分泌区的大小如何限制基于扩散的生长。该模型预测，扩散介导的生长取决于尖端胞吐区域的大小，并且基于扩散的生长将显著慢于正常细胞生长。为了进一步探索分泌区的大小，我们使用了细胞壁降解酶混合物，并确定分泌区在尖端的直径小于6 mm。两者合计，我们的研究结果强调了在极化生长的主动运输的要求，并提供了重要的洞察囊泡分泌过程中的尖端生长。
F-actin has been shown to be essential for tip growth in an array of plant models, including Physcomitrella patens. One hypothesis is that diffusion can transport secretory vesicles, while actin plays a regulatory role during secretion. Alternatively, it is possible that actin-based transport is necessary to overcome vesicle transport limitations to sustain secretion. Therefore, a quantitative analysis of diffusion, secretion kinetics, and cell geometry is necessary to clarify the role of actin in polarized growth. Using fluorescence recovery after photobleaching analysis, we first show that secretory vesicles move toward and accumulate at the tip in an actin-dependent manner. We then depolymerized F-actin to decouple vesicle diffusion from actin-mediated transport and measured the diffusion coefficient and concentration of vesicles. Using these values, we constructed a theoretical diffusion-based model for growth, demonstrating that with fast-enough vesicle fusion kinetics, diffusion could support normal cell growth rates. We further refined our model to explore how experimentally extrapolated vesicle fusion kinetics and the size of the secretion zone limit diffusion-based growth. This model predicts that diffusion-mediated growth is dependent on the size of the region of exocytosis at the tip and that diffusion-based growth would be significantly slower than normal cell growth. To further explore the size of the secretion zone, we used a cell wall degradation enzyme cocktail and determined that the secretion zone is smaller than 6 mm in diameter at the tip. Taken together, our results highlight the requirement for active transport in polarized growth and provide important insight into vesicle secretion during tip growth.