水稻钾离子通道蛋白OsAKT2的功能鉴定（Plant Physiology）

Abstract

背景回顾：AKT2 potassium (K⁺) channels are members of the plant Shaker family which mediate dual-directional K+ transport with weak voltage-dependency. 

主要发现：Here we show that OsAKT2 of rice (Oryza sativa) functions mainly as an inward rectifier with strong voltage-dependency and acutely suppressed outward activity. 

结果1-关键突变：This is attributed to the presence of a unique K191 residue in the S4 domain. The typical bi-directional leak-like property was restored by a single K191R mutation, indicating that this functional distinction is an intrinsic characteristic of OsAKT2. 

结果2-拟南芥AKT2蛋白反向突变：Further, the opposite R195K mutation of AtAKT2 changed the channel to an inward-rectifier similar to OsAKT2. 

结果3-水稻AKT2蛋白的调控因子：OsAKT2 was modulated by OsCBL1/OsCIPK23, evoking the outward activity and diminishing the inward current.

结果4-拟南芥akt2突变体：The physiological relevance in relation to the rectification diversity of OsAKT2 was addressed by functional assembly in the Arabidopsis (Arabidopsis thaliana) akt2 mutant. Overexpression of OsAKT2 complemented the K+ deficiency in the phloem sap and leaves of the mutant plants but did not significantly contribute to the transport of sugars. However, the expression of OsAKT2-K191R overcame both the shortage of phloem K+ and sucrose of the akt2 mutant, which was comparable to the effects of the overexpression of AtAKT2, while the expression of the inward mutation AtAKT2-R195K resembled the effects of OsAKT2. Additionally, overexpression of OsAKT2 ameliorated the salt tolerance of Arabidopsis.

摘 要

AKT2钾离子通道是植物Shaker家族的成员，介导钾离子的双向运输，具有弱电压依赖性。本文中，作者发现水稻的OsAKT2功能主要是介导钾离子的内流，具有具有非常强的电压依赖性和强烈的钾离子外流活性抑制。而这主要是归因于OsAKT2蛋白S4结构域中独特的K191残基。通过将OsAKT2蛋白191号位上的K突变为R，就能够恢复其双向介导钾离子流的特性，说明了这种功能差异是OsAKT2蛋白本身固有的特点。另外，将拟南芥的AtAKT2蛋白191位上的R反向突变为K，会导致其转变为类似于OsAKT2的钾离子内流蛋白。OsAKT2受到OsCBL1/OsCIPK23的调控，激活其外流活性，抑制内流活性。作者通过对拟南芥akt2突变体的功能组装，鉴定了与OsAKT2蛋白整流多样性的生理相关性。过表达OsAKT2基因能够拯救突变体韧皮部汁液和叶片中的钾离子缺陷，但是并不能显著作用于蔗糖的转运。但是，OsAKT2-K191R的表达就能够同时拯救akt2突变体中韧皮部钾离子和蔗糖的储存缺陷，能够达到与过表达AtAKT2类似的效果，而过表达拟南芥的内流突变AtAKT2-R195K基因则获得与OsAKT2类似的效果。另外，过表达OsAKT2基因能够增强拟南芥的耐盐性。

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