Characterization of two HKT1 homologues from Eucalyptus camaldulensis that display intrinsic osmosensing capability
Characterization of two HKT1 homologues from Eucalyptus camaldulensis that display intrinsic osmosensing capability
复制标题
DOI：
10.1104/pp.127.1.283
复制
发表时间：
2001-09-01
期刊：
影响因子：
7.4
通讯作者：
Schachtman, DP
中科院分区：
文献类型：
--
作者：
Liu, WH;Fairbairn, DJ;Schachtman, DP
植物具有多种钾（K(+)）吸收和外排机制，这些机制在植物组织中表达，以完成不同的生理功能。在植物分子水平上已经鉴定出几种不同类型的K（+）通道和载体。从小麦（Triticum aestivum）、拟南芥（Arabidopsis）和桉树（Eucalyptus camaldulensis）中克隆了HKT1超家族的K（+）转运蛋白。这些转运体的功能特征以及主要结构在细菌和真菌基因组中发现的同源物是多种多样的。在这篇报告中，我们详细描述了从非洲爪蟾卵母细胞中分离的两个cdna的功能特征，这两个cdna编码属于K(+)/Na（+）转运蛋白的HKT1超家族。在表达echkt的卵母细胞中，Na（+）可以促进K（+）的转运，但在没有Na（+）的情况下，K（+）也可以转运。正如HKT1和AtHKT1所证明的那样，Na+在没有K+的情况下被运输。综上所述，茶树转运体对HKT1和AtHKT1的离子选择性存在一定的相似性和差异性。HKT1和EcHKT之间的一个显著区别是对溶液外部渗透压变化的敏感性。低渗溶液使表达HKT1或未注射HKT1的卵母细胞的EcHKT诱导电流增加100%。这些渗透敏感电流不受电压的增强，可能介导水通量。这些渗透诱导的电流增加的生理功能可能与油松所居住的生态位有关，这些生态位周期性地被淹没。因此，EcHKT的渗透感应功能可能为该物种在一定条件下维持K（+）稳态提供了竞争优势。
Plants have multiple potassium (K(+)) uptake and efflux mechanisms that are expressed throughout plant tissues to fulfill different physiological functions. Several different classes of K(+) channels and carriers have been identified at the molecular level in plants. K(+) transporters of the HKT1 superfamily have been cloned from wheat (Triticum aestivum), Arabidopsis, and Eucalyptus camaldulensis. The functional characteristics as well as the primary structure of these transporters are diverse with orthologues found in bacterial and fungal genomes. In this report, we provide a detailed characterization of the functional characteristics, as expressed in Xenopus laevis oocytes, of two cDNAs isolated from E. camaldulensis that encode proteins belonging to the HKT1 superfamily of K(+)/Na(+) transporters. The transport of K(+) in EcHKT-expressing oocytes is enhanced by Na(+), but K(+) was also transported in the absence of Na(+). Na+ is transported in the absence of K+ as has been demonstrated for HKT1 and AtHKT1. Overall, the E. camaldulensis transporters show some similarities and differences in ionic selectivity to HKT1 and AtHKT1. One striking difference between HKT1 and EcHKT is the sensitivity to changes in the external osmolarity of the solution. Hypotonic solutions increased EcHKT induced currents in oocytes by 100% as compared with no increased current in HKT1 expressing or uninjected oocytes. These osmotically sensitive currents were not enhanced by voltage and may mediate water flux. The physiological function of these osmotically induced increases in currents may be related to the ecological niches that E. camaldulensis inhabits, which are periodically flooded. Therefore, the osmosensing function of EcHKT may provide this species with a competitive advantage in maintaining K(+) homeostasis under certain conditions.