Dhonukshe Pankaj
Department of Biology; Utrecht University; Utrecht, The Netherlands.
Commun Integr Biol. 2009 Mar;2(2):184-90. doi: 10.4161/cib.7715.
Auxin efflux carrier PIN proteins have been intensively investigated as they are the first polar cargos to be identified in plants with a direct relevance for plant patterning. Based on their polar localization; PIN proteins direct the intercellular flow of signaling molecule auxin and thus bear a rate limiting effect on the formation of auxin activity gradients. With this influence on directionality and extent of auxin transport PINs play crucial roles in plant body organization. Many factors such as vesicle trafficking regulator ARF-GEF GNOM, a kinase PINOID, a retromer complex and membrane sterol composition influence polar PIN localization. Recent work uncovers the mechanism that generates default PIN polarity. Real time PIN tracking reveals that PIN polarity is generated from initially non-polar secretion via endocytosis and subsequent polar recycling. In addition, the Rab5 endocytic pathway emerges to be important for polar PIN localization as Rab5 interference causes non-polar distribution of PINs. This non-polar distribution of PINs during embryogenesis transiently alters auxin activity gradients and changes organ identity by transforming embryonic leaf cells to root fates. These findings for the first time link PIN polarity-based auxin activity gradient to cell fate decisions and thus demonstrate morphogen (a substance influencing cell fates on its concentration gradient) characters of auxin. They also suggest an auxin activity distribution-dependent sensing module that executes differential apical and basal developmental program during plant embryogenesis.
生长素输出载体PIN蛋白已得到深入研究,因为它们是植物中首批被鉴定出的极性货物,与植物模式形成直接相关。基于其极性定位,PIN蛋白引导信号分子生长素的细胞间流动,因此对生长素活性梯度的形成具有限速作用。凭借对生长素运输方向和程度的这种影响,PIN蛋白在植物体组织中发挥着关键作用。许多因素,如囊泡运输调节因子ARF-GEF GNOM、激酶PINOID、逆转录复合物和膜甾醇组成,都会影响PIN蛋白的极性定位。最近的研究揭示了产生默认PIN极性的机制。实时PIN追踪显示,PIN极性是通过内吞作用从最初的非极性分泌以及随后的极性循环产生的。此外,Rab5内吞途径对于PIN蛋白的极性定位似乎很重要,因为Rab5干扰会导致PIN蛋白的非极性分布。胚胎发育过程中PIN蛋白的这种非极性分布会短暂改变生长素活性梯度,并通过将胚胎叶细胞转变为根命运来改变器官特性。这些发现首次将基于PIN极性的生长素活性梯度与细胞命运决定联系起来,从而证明了生长素的形态发生素(一种根据其浓度梯度影响细胞命运的物质)特性。它们还提出了一种生长素活性分布依赖性传感模块,该模块在植物胚胎发育过程中执行不同的顶端和基部发育程序。