Department of Botany and Plant Sciences and Center for Plant Cell Biology, Institute for Integrative Genome Biology, University of California-Riverside, Riverside, CA 92521, USA.
J Cell Sci. 2010 Feb 1;123(Pt 3):340-50. doi: 10.1242/jcs.039180. Epub 2010 Jan 5.
Rapid tip growth allows for efficient development of highly elongated cells (e.g. neuronal axons, fungal hyphae and pollen tubes) and requires an elaborate spatiotemporal regulation of the growing region. Here, we use the pollen tube as a model to investigate the mechanism regulating the growing region. ROPs (Rho-related GTPases from plants) are essential for pollen tip growth and display oscillatory activity changes in the apical plasma membrane (PM). By manipulating the ROP activity level, we showed that the PM distribution of ROP activity as an apical cap determines the tip growth region and that efficient tip growth requires an optimum level of the apical ROP1 activity. Excessive ROP activation induced the enlargement of the tip growth region, causing growth depolarization and reduced tube elongation. Time-lapse analysis suggests that the apical ROP1 cap is generated by lateral propagation of a localized ROP activity. Subcellular localization and gain- and loss-of-function analyses suggest that RhoGDI- and RhoGAP-mediated global inhibition limits the lateral propagation of apical ROP1 activity. We propose that the balance between the lateral propagation and the global inhibition maintains an optimal apical ROP1 cap and generates the apical ROP1 activity oscillation required for efficient pollen-tube elongation.
快速的尖端生长允许高效地发育出高度伸长的细胞（例如神经元轴突、真菌菌丝和花粉管），并需要对生长区域进行精细的时空调节。在这里，我们使用花粉管作为模型来研究调节生长区域的机制。ROP（植物中的 Rho 相关 GTP 酶）对于花粉管的尖端生长是必不可少的，并且在顶端质膜（PM）中显示出振荡性的活性变化。通过操纵 ROP 活性水平，我们表明 ROP 活性在 PM 中的分布作为一个顶端帽决定了尖端生长区域，并且有效的尖端生长需要顶端 ROP1 活性的最佳水平。过度的 ROP 激活诱导尖端生长区域的扩大，导致生长去极化和管伸长减少。延时分析表明，顶端 ROP1 帽是通过局部 ROP 活性的侧向传播产生的。亚细胞定位和增益和损耗功能分析表明，RhoGDI-和 RhoGAP 介导的全局抑制限制了顶端 ROP1 活性的侧向传播。我们提出，侧向传播和全局抑制之间的平衡维持了最佳的顶端 ROP1 帽，并产生了高效花粉管伸长所需的顶端 ROP1 活性振荡。
