Abstract：
Cytokinins (CKs) are phytohormones structurally similar to purines that play important roles in various aspects of plant physiology and development. The local and long-distance distribution of CKs is very important to control their action throughout the plant body. Over the past decade, several novel CK transporters have been described, many of which have been linked to a physiological function rather than simply their ability to transport the hormone in vitro. Purine permeases, equilibrative nucleotide transporters and ATP-binding cassette transporters are involved in the local and long-range distribution of CK. In addition, members of the Arabidopsis AZA-GUANINE RESISTANT (AZG) protein family, AZG1 and AZG2, have recently been shown to mediate CK uptake at the plasma membrane and endoplasmic reticulum. Despite sharing ∼50% homology, AZG1 and AZG2 have unique transport mechanisms, tissue-specific expression patterns, and subcellular localizations that underlie their distinct physiological functions. AZG2 is expressed in a small group of cells in the overlying tissue around the lateral root primordia, where its expression is induced by auxins and it is involved in the regulation of lateral root growth. AZG1 is ubiquitously expressed, with high levels in the division zone of the root apical meristem. Here, it binds and stabilises the auxin efflux carrier PIN1, thereby shaping root architecture, particularly under salt stress. This review highlights the latest findings on the protein properties, transport mechanisms and cellular functions of this new family of CK transporters and discusses perspectives for future research in this field.
摘要：
细胞分裂素（CKs）是结构上类似于嘌呤的植物激素，在植物生理和发育的各个方面发挥重要作用。CKs的局部和远距离分布对于控制其在整个植物体中的作用非常重要。在过去的十年里，已经描述了几种新型CK转运蛋白，其中许多与生理功能有关，而不仅仅是它们在体外运输激素的能力。嘌呤permeases，平衡核苷酸转运蛋白和ATP结合盒转运蛋白参与CK的局部和远程分布。此外,拟南芥AZA-GUANINE抗性（AZG）蛋白家族的成员，AZG1和AZG2最近被证明在质膜和内质网介导CK的摄取。尽管有50%的同源性，AZG1和AZG2具有独特的运输机制，组织特异性表达模式，以及构成其独特生理功能基础的亚细胞定位。AZG2在侧根原基周围的上覆组织中的一小组细胞中表达，其中其表达由生长素诱导，并且参与侧根生长的调节。AZG1普遍表达，在根尖分生组织的分裂区具有高水平。这里,它结合并稳定生长素外排载体PIN1，从而塑造根结构，特别是在盐胁迫下。这篇评论强调了蛋白质特性的最新发现，这个新的CK转运蛋白家族的转运机制和细胞功能，并讨论了该领域未来研究的前景。
