Department of Biology, Utrecht University, Utrecht, The Netherlands.
Plant Signal Behav. 2011 Sep;6(9):1333-7. doi: 10.4161/psb.6.9.16611.
The analysis of cell polarity in plants is fueled by the discovery and analysis of auxin efflux carrier PIN proteins that show polar localizations in various plant cell types in line with their roles in directional cell to cell auxin transport. As this asymmetry in cellular PIN localization drives directional auxin fluxes, abnormalities in PIN localizations modify auxin transport culminating into range of auxin distribution defective phenotypes. Because of this influence of PIN localization on plant development via changes in auxin distribution, mechanisms establishing, maintaining and altering PIN polarity are of intense interest in the plant field during the recent years. Recent findings suggest that two categories of molecules, namely AGC-3 kinase family members PINOID, WAG1, WAG2 and ARF-GEF family member GNOM predominantly influence the polar localization of PINs. The emerging mechanism for AGC-3 kinases and ARF-GEF action suggest that AGC-3 kinases predominantly phosphorylate PINs at the plasma membrane for eventual PIN internalization and PIN sorting into ARF-GEF GNOM independent polar recycling pathways. In case of mutant for AGC-3 kinases or mutations in AGC-3 kinase-targeted PIN residues, much less phosphorylated PINs are recruited into ARFGEF GNOM-dependent polar recycling pathway. When ARF-GEF GNOM is inactive, the bias is shifted for rerouting less efficiently phosphorylated PINs into GNOM-independent polar recycling pathways that generally prefer efficiently phosphorylated PINs. Thus, balance shifts between the extent of AGC-3 kinase mediated PIN phosphorylation and the functioning of ARFGEF instruct PIN polarity establishment and/or PIN polarity alterations. Recent studies report utilization of this AGC-3 kinase and ARF-GEF PIN polarity regulation module during diverse developmental and response programs including shoot patterning, root growth, phototropism, gravitropism, organogenesis, leaf epidermal cell indentations and fruit valve margin formation. Based on these findings the same theme of phosphorylated PIN sorting into differential polar recycling pathways for PIN polarity establishment and alteration seems to be employed in a context-dependent manner.
植物细胞极性分析得益于生长素外排载体 PIN 蛋白的发现和分析，这些蛋白在各种植物细胞类型中表现出极性定位，与它们在定向细胞间生长素运输中的作用一致。由于这种细胞内 PIN 定位的不对称性驱动了生长素的定向流动，PIN 定位的异常改变了生长素的运输，最终导致了一系列生长素分布缺陷表型。由于 PIN 定位通过改变生长素分布对植物发育的这种影响，近年来，植物领域对建立、维持和改变 PIN 极性的机制产生了浓厚的兴趣。最近的研究结果表明，两类分子，即 AGC-3 激酶家族成员 PINOID、WAG1、WAG2 和 ARF-GEF 家族成员 GNOM，主要影响 PIN 的极性定位。AGC-3 激酶和 ARF-GEF 作用的新兴机制表明，AGC-3 激酶主要在质膜上磷酸化 PIN，最终导致 PIN 内化和 PIN 分选到 ARF-GEF GNOM 独立的极性再循环途径。在 AGC-3 激酶的突变体或 AGC-3 激酶靶向的 PIN 残基的突变情况下，募集到 ARF-GEF GNOM 依赖的极性再循环途径中的磷酸化 PIN 要少得多。当 ARF-GEF GNOM 失活时，偏向于将效率较低磷酸化的 PIN 重新路由到 GNOM 独立的极性再循环途径的程度会发生变化，而后者通常更喜欢效率较高磷酸化的 PIN。因此，AGC-3 激酶介导的 PIN 磷酸化程度和 ARF-GEF 功能之间的平衡变化指导了 PIN 极性的建立和/或 PIN 极性的改变。最近的研究报告称，在包括分枝模式、根生长、向光性、向重力性、器官发生、叶表皮细胞凹陷和果实瓣膜边缘形成在内的多种发育和响应程序中，利用了这种 AGC-3 激酶和 ARF-GEF PIN 极性调节模块。基于这些发现，用于建立和改变 PIN 极性的磷酸化 PIN 分选到不同的极性再循环途径的主题似乎以依赖于上下文的方式被采用。
