拟南芥高亲和性K<sup>+</sup>载体蛋白基因cDNA克隆及其序列特征分析

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王丽, 张俊莲, 张金文, 刘玉汇, 白江平, 余斌, 杨宏羽, 王蒂. 拟南芥高亲和性K⁺载体蛋白基因cDNA克隆及其序列特征分析 . 22(6): 230-238
WANG Li, ZHANG Jun-lian, ZHANG Jin-wen, LIU Yu-hui, Bai Jiang-ping, YU Bin, YANG Hong-yu, WANG Di. Cloning and analysis of sequence characteristics of cDNA encoding the AtHKT1 gene from Arabidopsis thaliana leaves . Acta Prataculturae Sinica, 22(6): 230-238 复制到剪切板

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拟南芥高亲和性K⁺载体蛋白基因cDNA克隆及其序列特征分析

王丽^1,^2,³, 张俊莲^1,^3,^4*,^*, 张金文^1,^3,⁴, 刘玉汇^1,³, 白江平^1,^3,⁴, 余斌^1,³, 杨宏羽^1,^3,⁴, 王蒂^1,^3,^4*,^*

1.甘肃省作物遗传改良与种质创新重点实验室,甘肃兰州730070

2.甘肃农业大学生命科学技术学院,甘肃兰州730070

3.甘肃省干旱生境作物学重点实验室,甘肃兰州 730070

4.甘肃农业大学农学院,甘肃兰州730070

*通讯作者。E-mail:zhangjl@gsau.edu.cn,wangd@gsau.edu.cn

作者简介:王丽(1981-),女,甘肃兰州人,讲师,在读博士。E-mail:39726821@qq.com

基金:高等学校博士学科点专项基金项目(20106202110007),国家科技支撑计划项目(2012BAD06B03),甘肃省干旱生境作物学重点实验室开放基金(GSCS-2012-12)和甘肃农业大学科技创新基金项目(GAU-CX1024)资助

摘要

以NaCl胁迫处理的拟南芥幼苗叶片为材料,用RNA提取试剂盒抽提总RNA,通过RT-PCR技术和DNA序列测定分析,证实获得了拟南芥高亲和性K⁺载体蛋白基因( AtHKT1)的cDNA序列。该cDNA全长1521 bp,包括506个氨基酸和1个终止密码子序列,且与原序列(accession number AF237672)同源性为99.34%,但与其他科植物 HKT1基因同源性较低,注册该基因到GenBank中,注册号为AY685182。利用生物信息学相关软件分析预测 AtHKT1基因蛋白质功能和结构,结果发现,该蛋白分子量为57.45 kD,理论等电点为9.33;氨基酸序列中第1~40个氨基酸属信号肽序列;第152~500个氨基酸属Trk H阳离子转运体蛋白保守结构域,并存在蛋白激酶C,酪氨酸蛋白激酶,依赖cAMP/cGMP蛋白激酶磷酸化,糖基化和豆蔻酰化等功能位点;该基因编码的蛋白有10个跨膜结构,N末端、C末端及中部等多个跨膜区具疏水性,符合载体类运输蛋白特点。表明本研究获得了拟南芥 AtHKT1基因。

关键词: 拟南芥; 高亲和性K+载体蛋白; RT-PCR技术; 生物信息学分析

中图分类号:Q943.2 文献标志码:A 文章编号:1004-5759(2013)06-0230-09

Cloning and analysis of sequence characteristics of cDNA encoding the AtHKT1 gene from Arabidopsis thaliana leaves

WANG Li^1,^2,³, ZHANG Jun-lian^1,^3,⁴, ZHANG Jin-wen^1,^3,⁴, LIU Yu-hui^1,³, Bai Jiang-ping^1,^3,⁴, YU Bin^1,³, YANG Hong-yu^1,^3,⁴, WANG Di^1,^3,⁴

1.Gansu Key Laboratory of Crop Genetic & Germplasm Enhancement, Lanzhou 730070, China

2.College of Life Sciences and Technology,Gansu Agricultural University, Lanzhou 730070, China

3.Gansu Provincial Key Lab of Aridland Crop Science, Lanzhou 730070, China

4.College of Agronomic, Gansu Agricultural University,Lanzhou 730070, China

Abstract

The full length coding sequence of AtHKT1 was cloned via RT-PCR (reverse transcription-polymerase chain reaction) from the leaves of Arabidopsis thaliana seedling under NaCl stress. The full-length cDNA contained 1521 bp and encoded a polypeptide of 506 amino acids and a termination codon. The sequence shared 99.34% homology with the reported sequence (accession number AF237672), but the homologies were very low compared with similar genes from other plants. The gene was submitted to GenBank and was given the registration number AY685182. Bioinformatics softwares were used to predict and analyze the protein function and structure of the AtHKT1 gene cDNA sequence. The molecular weight of the deduced polypeptide of AtHKT1 was 57.45 kD. The theoretical pI was 9.33. The N-terminal amino acids from 1 to 40 formed a classic signal peptide sequence. The peptide from 152 to 500 was a Trk H cation transporter conserved domain. It might also carry protein kinase C, tyrosine kinase, cAMP-and cGMP-dependent protein kinase phosphorylation, glycosylation, N-myristoylation sites and other function sites. The deduced peptide contained 10 transmembrane domains. The transmembrane domains near the N-terminus, the C-terminus and the middle part of the peptide displayed high hydrophobicity. Therefore, it is suggested that the gene product of AtHKT1 might play roles in facilitating cation transportation.

Keyword: Arabidopsis thaliana; high-affinity potassium transporter; RT-PCR; bioinformatic analysis

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钾是植物生长发育必需的大量元素, 参与植物许多生理生化过程, 包括酶活性调节、蛋白质合成及渗透调节等, 保持胞质内较高K⁺/Na⁺对植物生长起着非常重要的作用^[1]。盐胁迫时, 大量Na⁺从根部进入植物体内, 抑制K⁺的吸收, K⁺/Na⁺降低, 导致植物受害^[2]。研究表明, 植物的耐盐性与其维持体内K⁺、Na⁺平衡的能力密切相关, 具有高K⁺/Na⁺的植物有较强的耐盐性^[3]。因此, 限制Na⁺吸收、增加Na⁺外排, 同时保证K⁺吸收, 维持细胞质高K⁺/Na⁺可抵御过量的Na⁺对植物造成的伤害^[4]。HKT(high-affinity K⁺ transporter)类蛋白属于一个广泛存在于植物、真菌、真细菌和古细菌中的K⁺转运体超级家族, 具有可以调节植物体内K⁺/Na⁺平衡的能力^[5]。

自1994年Schachtman和Schroeder^[6]从小麦(Triticum aestivum)幼苗根cDNA表达文库中克隆到第1个高亲和性K⁺载体蛋白基因-TaHKT1以来, 陆续在拟南芥(Arabidopsis thaliana)^[7]、碱蓬(Suaeda salsa)^[5]、芦苇(Phragmites australis)^[8]、水稻(Oryza sativa)^[9]、冰叶日中花(Mesembryanthemum crystallinum)^[10]、桉树(Eucalyptus camaldulensis)^[11]、大麦(Hordeum vulgare)^[12]、商陆(Phytolacca acinosa)^[13]、海蓬子(Salicornia bigelovii)^[14]等多种植物中克隆了其同源蛋白基因。早期研究认为, HKT1蛋白是Na⁺吸收和运输的载体, 降低HKT1的表达, 可能会提高植物抗盐性, 如Laurie等^[15]研究发现, 表达反义HKT1基因的小麦植株较野生型耐盐胁迫能力更强; Horie等^[16]比较耐盐水稻和盐敏感水稻时发现, 抗盐性高的水稻HKT1基因的表达量在盐胁迫时降低, 而盐敏感型水稻HKT1的表达量一直维持在很高水平; Rus等^[17]研究发现拟南芥AtHKT1基因在sos3-1突变体的过量表达增强了突变体植株在低K⁺环境下对Na⁺的敏感性及植株的缺K⁺症状, AtHKT1基因可转运Na⁺进入细胞、调控根部Na⁺的吸收。然而近期更多的研究证明, AtHKT1转运蛋白在提高植物耐盐性中可能具有重要的积极作用, 如Mä ser等^[18]认为拟南芥AtHKT1基因参与调控Na⁺在根和地上部分的分配; Berthomieu等^[19]认为AtHKT1参与Na⁺通过韧皮部汁液从地上部分至根部的再循环过程, 降低叶中Na⁺积累; Sunarpi等^[20]认为在高盐环境下, AtHKT1基因调节Na⁺从根部木质部卸载。特别是最近的研究又发现, AtHKT1基因既不调控Na⁺从地上部到根部的再循环, 也不调节Na⁺以内流的形式进入根部, 而是将Na⁺直接滞留在根的木质部中, 加载Na⁺进入根部液泡, 从而降低Na⁺从根到茎的运输^{[21, 22, 23, 24, 25, 26]}。由此可见, AtHKT1基因在植株中的耐盐表达调控机制仍有争议, 目前尚未见利用该基因改良作物耐盐性的报道。

为了研究AtHKT1基因参与植物耐盐调控机制, 更好地发挥其作用, 本研究以拟南芥为材料, 利用RT-PCR技术, 在盐胁迫条件下进行AtHKT1基因的分离克隆。进一步通过该基因编码蛋白特性及结构分析, 初步确定该基因功能和特点, 为进一步研究该基因功能及改良作物耐盐性奠定基础。

1 材料与方法

1.1 材料

1.1.1 植物材料拟南芥种子用70%酒精浸泡30 s, 0.1% HgCl₂处理5 min, 无菌水冲洗5次后接入MS基本培养基上, 在25℃、12 h/d光照下培养。当幼苗生长至14 d时, 将160 mmol/L的NaCl水溶液倒入培养基上, 胁迫幼苗12 h待用。本试验在2004年进行。

1.1.2 菌株和载体大肠杆菌(Escherichia coli)菌株为DH5α 的感受态细胞; T-载体为pGEM-T Easy Vector(购自Promega公司), 抗性标记为氨苄青霉素(Amp^r)。

1.1.3 酶和试剂 SuperscriptⅡ 逆转录试剂盒购自Promega公司; 各种限制性内切酶、Pyrobest^TMDNA聚合酶和T₄DNA连接酶购自TaKaRa公司; TaqDNA聚合酶和TRIzol一步法RNA提取试剂盒购自鼎国公司; DNA凝胶回收试剂盒购自上海开瑞公司; 其他生化试剂为国产分析纯。

1.2 AtHKT1基因cDNA克隆

1.2.1 逆转录合成cDNA第1链 1)总RNA提取。用TRIzol一步法RNA提取试剂盒抽提盐胁迫下的拟南芥叶片总RNA, 提取方法见试剂盒说明书。提取的总RNA在经焦碳酸二乙酯(DEPC)处理的1%琼脂糖凝胶上电泳, EB染色后检查RNA完整性; 2)cDNA第1链合成。在提取的7.5 μ L RNA中加入1 μ L Oligo(dT), 65℃加热8 min, 室温自然冷却; 向上述混合液中加入4 μ L 25 mmol/L的MgCl₂、4 μ L 5× buffer、2 μ L 10 mmol/L dNTP和0.5 μ L的RNase, 混匀后加入AMV反转录酶, 再次混匀后42℃下保温30 min, 99℃下煮5 min, -20℃保存。

1.2.2 PCR扩增根据已发表的拟南芥AtHKT1基因序列(accession number AF237672), 设计1对引物, 即上游引物p1:5'-CGGGATCC(BamHⅠ )ATGGACAGAGTGGTGGCAAAAATAG-3'和下游引物p2:5'-CGGAGCTC(SacⅠ )TTAGGAAGACGAGGGGTAAAGTATCC-3', 由北京赛百盛公司合成。扩增反应体系为25 μ L, 由1 μ L cDNA模板、2.5 μ L 10× buffer、1 μ L dNTP(10 mmol/L)、1 μ L引物p1(10 μ mol/L)、1 μ L引物p2(10 μ mol/L)、0.5 μ L Pyrobest^TMDNA聚合酶、18 μ L dd H₂O组成。扩增条件为:94℃预变性1 min后, 进行94℃ 50 s、53℃ 50 s、72℃ 120 s的35个循环, 再在72℃下延伸10 min。扩增产物EB染色后进行1%琼脂糖凝胶电泳检测。

1.2.3 AtHKT1基因cDNA与T-载体连接扩增产物经1%琼脂糖凝胶电泳分离后回收, 回收方法见上海开瑞公司凝胶回收试剂盒说明书。扩增产物利用TaqDNA聚合酶对其加A, 然后与T-载体相连, 连接产物转化感受态细胞。

1.3 重组质粒的鉴定

将转化细胞涂在含50 μ g/mL Amp^r、20 mg/mL 5-溴-4-氯-3-吲哚-β -D-半乳糖苷(X-gal)和100 mg/mL异丙基-β -D-硫代半乳糖苷(IPTG)的LB平板上进行蓝白斑筛选。对所获得的白斑通过滞后质粒、PCR扩增、BamHⅠ 和SacⅠ 双酶切鉴定, -80℃保存菌株。

1.4 序列测定及分析

送鉴定后的白斑菌株到上海博亚公司测序, 所测序列用DNAMAN virsion 6.0软件进行分析。然后通过NCBI网站的Blast X和Blast P程序进行序列相似性分析; 利用 InterProScan (http://www.ebi.ac.uk/Tools/InterProScan/)进行信号肽分析和氨基酸保守性预测; 用MEGA4.0软件进行氨基酸序列比对和HKT类蛋白质序列系统进化树分析; 链接至http://expasy.org/tools/protparam.html网站进行蛋白质理化性质分析; 利用PredictProtein Server(http://www.predictprotein.org/)进行蛋白质结构域分析; 利用TMHMM Serverv 2.0(http://www.cbs.dtu.dk/services/TMHMM-2.0)程序分析蛋白质序列跨膜区; 利用ProtScale(http://expasy.org/tools/protscale.html)分析氨基酸序列的疏水性。

2 结果与分析

2.1 拟南芥AtHKT1基因的分离

利用TRIzol一步法RNA提取试剂盒提取盐胁迫下的拟南芥叶片总RNA, 琼脂糖凝胶电泳显示, 总RNA 5S、18S和28S三条带清晰、完整(图1), 说明RNA完整性良好。利用RT-PCR试剂盒进行cDNA第1链合成后, 利用1对特异性引物及Pyrobest^TMDNA聚合酶, 以cDNA为模板进行目的基因扩增, 期望获得约1521 bp大小的DNA片段。对扩增产物电泳检查结果表明, 扩增产物与预期片段的大小基本一致(图2), 说明可能获得了AtHKT1基因的cDNA克隆。

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	图1 拟南芥总RNAFig.1 Total RNA of A. thaliana1, 2:总RNA Total RNA.

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	图2 拟南芥AtHKT1基因的PCR扩增Fig.2 PCR amplification of AtHKT1 gene

2.2 重组菌株获得

因pGEM-T Easy Vector载体多克隆位点位于LacZ基因编码区, 外源基因插入将改变LacZ基因编码序列的完整性, 影响β -半乳糖苷酶活性, 致使重组子在X-gal/IPTG平板上呈白色, 而非重组子呈蓝色。选取白色菌株进行滞后质粒筛选(图3), 初步淘汰假阳性, 然后对阳性菌株进行PCR(图4)及双酶切(BamHⅠ 和SacⅠ )鉴定(图5)。结果显示, 扩增到或切下约1521 bp大小的DNA片段, 说明可能获得了携带有AtHKT1基因的重组菌株。

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	图3 T-载体上滞后质粒筛选Fig.3 Identification of delayed plasmid of T-vector

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	图4 白斑滞后质粒PCR鉴定Fig.4 Identification of white color plasmid by PCRM:MakerⅤ 分子量标记DNA marker Ⅴ ; 1~5:白斑滞后质粒White color plasmid.

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	图5 白斑滞后质粒BamH Ⅰ 和SacⅠ 酶切鉴定Fig.5 Identification of white color plasmid by BamH Ⅰ and Sac Ⅰ

2.3 AtHKT1基因cDNA序列及蛋白序列分析

2.3.1 cDNA序列特征分析将经鉴定的重组菌株交上海博亚生物技术公司测序。将测序结果与原序列(accession number AF237672)比较, 发现二者同源性高达99.34%。对测序结果分析后发现, 其开放阅读框架为1521 bp(图6), 包括506个氨基酸编码区和1个终止密码子(TAA)。该基因登记在GenBank中(accession number AY685182)。

用DNAMAN软件对该序列与GenBank中登记的部分物种的HKT1基因的cDNA序列进行同源性比较。结果发现, 该序列与其他学者登录的拟南芥AtHKT1基因同源性都很高, 达99.34%以上, 与同科盐芥同源性较高, 为84.00%, 与其他科植物同源性低, 为48.47%~57.34%(表1), 说明同科植物特别是同种植物, 该基因的保守性强, 而不同科植物的AtHKT1基因间差异较大。

2.3.2 蛋白质进化特征分析系统进化树分析发现, 10个物种的21个HKT蛋白被聚为9个类群, 拟南芥AtHKT1和同科的盐芥ThHKT1聚为一类, 亲缘关系最近; 禾本科水稻OsHKT3、OsHKT9、OsHKT7、OsHKT4聚为一类; 禾本科水稻OsHKT1、OsHKT2和芦苇PhaHKT1为一类; 禾本科大麦HvHKT1和小麦TaHKT1为一类; 番杏科冰花McHKT2、桃金娘科赤桉EcHKT1、EcHKT2和藜科碱蓬SsHKT1为一类; 禾本科水稻OsHKT8、OsHKT6、番杏科冰花McHKT1、藜科海蓬子SbHKT1单独聚为一类, 基本表现为同科尤其是同种同源性高、种间相对低的特点(图7)。

2.3.3 蛋白理化性质及结构域分析 Protparam软件预测AtHKT1 蛋白分子式为C₂₆₅₇H₄₁₂₆N₆₄₈O₇₂₅S₂₂, 分子量57.45 kD, 理论等电点为9.33, 带正电荷氨基酸残基数(Arg+Lys)为47, 带负电荷氨基酸残基数(Asp+Glu)为41, 不稳定系数为34.19, 为稳定碱性蛋白。该蛋白在第1~40个氨基酸残基处有1个信号肽序列(图6, 用“ · ” 表示)。在第152~500个氨基酸处有1个Trk H阳离子转运体蛋白保守结构域(图6, 用“ [ ]” 表示)。分别在第70~73, 128~131, 138~141, 185~188, 191~194, 260~263, 318~321, 339~342, 411~414个氨基酸残基处有9个酪蛋白激酶Ⅱ 磷酸化位点(图6, 用“ □” 表示), 表明该蛋白是一种真核细胞中普遍存在的信使非依赖性丝/苏氨酸蛋白激酶, 在细胞生存、生长、增殖及凋亡过程中具有重要功能。在第48~50, 185~187, 191~193, 260~262, 282~284, 413~415, 492~494和495~497个氨基酸处具有8个蛋白激酶C磷酸化位点(图6, 用“ ■” 表示), 能将靶蛋白的Ser/thr磷酸化, 从而激活细胞质中某些酶的活性, 参与生化反应调控; 还可与核中转录因子相互作用, 参与基因表达调控。该蛋白在第225~228个氨基酸处有1个依赖cAMP/cGMP蛋白激酶磷酸化位点[图6, 用“ ( )” 表示], 能在ATP存在的情况下使许多蛋白质特定的丝/苏氨酸残基磷酸化, 调节细胞的物质代谢和基因表达。此外, 在第261~267个氨基酸处[图6, 用“ { }” 表示], 该蛋白具有1个酪氨酸蛋白激酶磷酸化位点, 可将自身的酪氨酸磷酸化或将各种不同靶蛋白的酪氨酸磷酸化来实现信号传递, 其转导的信号通常与细胞生长、繁殖、分化、生存有关。位于第429~432个氨基酸处该蛋白具有1个N端糖基化位点(图6, 用“ =” 表示), 使蛋白质能够抵抗消化酶的作用、赋予蛋白质传导信号的功能、或某些蛋白只有在糖基化之后才能正确折叠。此外, 3个N端豆蔻酰化位点分别在第122~127, 394~399, 459~464个氨基酸处(图6, 用“ -” 表示)。

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	图6 拟南芥AtHKT1基因的cDNA序列及其推测的氨基酸序列Fig.6 Nucleotide sequence and deduced amino sequence of AtHKT1 cDNA of A. thaliana

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	图7 AtHKT1 蛋白与其他物种 HKT 类蛋白构建的系统进化树分析Fig.7 Phylogenetic tree analysis of AtHKT1 form A. thaliana with other reported HKT proteins

2.3.4 蛋白跨膜性及疏水性分析经TMHMM Serverv 2.0软件分析推测, AtHKT1 蛋白有10个跨膜区(21~43, 82~104, 158~180, 195~217, 230~252, 285~307, 343~365, 395~412, 425~447, 467~486), 其中395~412区域的跨膜螺旋长度为18个氨基酸残基, 467~486区域的跨膜螺旋长度为20个氨基酸残基, 其余区域均为23个氨基酸残基(图8)。利用ProtScale软件的Kyte and Doolittle算法对AtHKT1蛋白进行亲水/疏水性分析(图9)。在347~359区域的疏水性最强(最大值达3.467), 疏水性较强的区域有13个, 分别位于第22~39, 58~68, 80~93, 157~164, 170~181, 199~206, 231~238, 245~256, 283~306, 326~328, 397~411, 430~434, 476~484个氨基酸处; 在372~390区域的亲水性最强(分值为-2.900), 其次有5个区域(45~52, 127~131, 139~141, 259~276, 415~422)具有较强的亲水性。就整体来看, 该蛋白疏水性氨基酸均匀分布在整个肽链中, 占总氨基酸组成的46.64%, 疏水区域大于亲水区域, N末端、C末端及中部等多个跨膜区均具有疏水性, 整个多肽链表现为疏水性, 可认为拟南芥AtHKT1蛋白是疏水性蛋白, 符合载体类运输蛋白特点, 表明获得了跨膜运输蛋白基因— — AtHKT1基因。

表1 拟南芥AtHKT1基因cDNA与其他植物HKT1基因cDNA序列同源性比较 Table 1 Alignment of nucleotide sequence of AtHKT1 gene with other homologues

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	图8 AtHKT1 蛋白跨膜区分析Fig.8 The analysis of transmembrane of AtHKT1 polypeptide

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	图9 AtHKT1 氨基酸序列疏水性分析Fig.9 The analysis of hydrophobicity of AtHKT1 polypeptide

3 讨论

已有研究表明AtHKT1基因参与Na⁺的转运, 与植物耐盐性有关, 但关于其具体功能, 不同研究者存在着不同观点。早期研究认为, AtHKT1基因的过量表达可增加植株的盐敏感性^[17], 近期部分学者对该基因的作用有新解, 认为AtHKT1基因可调节Na⁺在根和茎中的分配以及从茎到根部的再循环^{[18, 19, 20]}, AtHKT1蛋白如果在拟南芥根部的中柱鞘及维管束过量表达, 会增加Na⁺在根部木质部薄壁组织及皮层中滞留, 减少Na⁺由根部转运至叶, 从而降低叶片中Na⁺浓度, 表明该基因在根部的过量表达可提高拟南芥植株的耐盐性, 但如果由组成型35S启动子驱动AtHKT1基因在整个植株中的过量表达却导致了转基因植株的盐敏感性, 说明AtHKT1基因的组织特异性表达与植株耐盐性关系密切^{[24, 25, 26]}。本研究根据GenBank中拟南芥高亲和性K⁺载体蛋白基因序列(AF237672)设计引物, 利用RT-PCR方法, 从拟南芥总RNA中扩增出目的cDNA片段。序列分析发现, 该cDNA片段的开放阅读框架为1521 bp, 包括506个氨基酸编码区和1个终止密码子(TAA)。该片段与GenBank中其他学者发表的拟南芥该基因cDNA序列(NM_117099)同源性为99.67%, 与同科盐芥(EF025500)cDNA同源性为84.00%, 蛋白质同源性为78%, 与其他科植物cDNA序列同源性较低, 为48.47%~57.34%, 蛋白质序列同源性为42.00%~51.00%。说明同一物种中该基因保守, 但不同物种间差异明显, 这与其他研究者对不同基因或不同物种同源性分析时的结论是一致的, 即属内同源性高, 属间相对低^{[27, 28, 29]}, 可见高亲和性K⁺载体蛋白在进化上也存在多样性。

本研究对克隆到的AtHKT1基因的cDNA片段利用相关软件进行了分析, 发现其具有1个Trk H阳离子转运体蛋白保守结构域和1个信号肽序列, 存在蛋白激酶C、酪氨酸蛋白激酶、酪蛋白激酶Ⅱ 磷酸化、依赖cAMP/cGMP蛋白激酶磷酸化、糖基化、豆蔻酰化等功能位点, 表明该基因具有阳离子转运功能。王景艳等^[30]认为植物通过离子外排和区域化降低Na⁺的毒害与植物跨膜运输蛋白有密切关系, AtHKT1蛋白疏水性及跨膜性分析表明, 该蛋白有10个跨膜区, 是疏水性蛋白, 符合载体类跨膜运输蛋白特点, 推测其与钾和钠离子的转运相关。本研究为该基因进一步功能研究奠定了基础。

The authors have declared that no competing interests exist.

参考文献

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2000

0.0

... 钾是植物生长发育必需的大量元素,参与植物许多生理生化过程,包括酶活性调节、蛋白质合成及渗透调节等,保持胞质内较高K⁺/Na⁺对植物生长起着非常重要的作用^[1] ...

2006

0.0

... 盐胁迫时,大量Na⁺从根部进入植物体内,抑制K⁺的吸收,K⁺/Na⁺降低,导致植物受害^[2] ...

2001

11.41

0.0

. 2001, 13(4):399-404 DOI:10.1016/S0955-0674(00)00227-1

Ion homeostasis during salt stress in plants

Abstract Recent progress has been made in the characterization of cation transporters that maintain ion homeostasis during salt stress in plants. Sodium–proton antiporters at the vacuolar (NHX1) and plasma membrane (SOS1) have been identified in Arabidopsis . SOS1 is regulated by the calcium-activated protein kinase complex SOS2—SOS3. In yeast, a transcription repressor, Sko1, mediates regulation of the sodium-pump ENA1 gene by the Hog1 MAP kinase. The recent visualization at the atomic level of the inhibitory site of sodium in the known target Hal2 has helped identify the interactions determining Na + toxicity.

... 研究表明,植物的耐盐性与其维持体内K⁺、Na⁺平衡的能力密切相关,具有高K⁺/Na⁺的植物有较强的耐盐性^[3] ...

2003

8.455

0.0

. 2003, 6(5):441-445

Regulation of ion homeostasis under salt stress

Department of Plant Sciences, University of Arizona, Tucson, Arizona 85721, USA. jkzhu@ag.arizona.edu

When under salt stress, plants maintain a high concentration of K(+) and a low concentration of Na(+) in the cytosol. They do this by regulating the expression and activity of K(+) and Na(+) transporters and of H(+) pumps that generate the driving force for transport. Although salt-stress sensors remain elusive, some of the intermediary signaling components have been identified. Evidence suggests that a protein kinase complex consisting of the myristoylated calcium-binding protein SOS3 and the serine/threonine protein kinase SOS2 is activated by a salt-stress-elicited calcium signal. The protein kinase complex then phosphorylates and activates various ion transporters, such as the plasma membrane Na(+)/H(+) antiporter SOS1.

PMID: 12972044

... 因此,限制Na⁺吸收、增加Na⁺外排,同时保证K⁺吸收,维持细胞质高K⁺/Na⁺可抵御过量的Na⁺对植物造成的伤害^[4] ...

2006

0.0

... HKT(high-affinity K⁺ transporter)类蛋白属于一个广泛存在于植物、真菌、真细菌和古细菌中的K⁺转运体超级家族,具有可以调节植物体内K⁺/Na⁺平衡的能力^[5] ...

... 自1994年Schachtman和Schroeder^[6]从小麦(Triticum aestivum)幼苗根cDNA表达文库中克隆到第1个高亲和性K⁺载体蛋白基因-TaHKT1以来,陆续在拟南芥(Arabidopsis thaliana)^[7]、碱蓬(Suaeda salsa)^[5]、芦苇(Phragmites australis)^[8]、水稻(Oryza sativa)^[9]、冰叶日中花(Mesembryanthemum crystallinum)^[10]、桉树(Eucalyptus camaldulensis)^[11]、大麦(Hordeum vulgare)^[12]、商陆(Phytolacca acinosa)^[13]、海蓬子(Salicornia bigelovii)^[14]等多种植物中克隆了其同源蛋白基因 ...

1994

38.597

0.0

. 1994, 370:655-658

Structure and transport mechanism of a high-affinity potassium uptake transporter from higher plants

Department of Biology, University of California, San Diego, La Jolla 92093-0116.

Potassium is the most abundant cation in higher plants and is crucial for plant nutrition, growth, tropisms, enzyme homeostasis and osmoregulation. K+ accumulation can be rate-limiting for agricultural production. K+ uptake from soils into roots is largely mediated by high-affinity K+ uptake (Km approximately 10-40 microM) (refs 1, 2, 5-7). But although K+ channels allow low-affinity K+ uptake, both the transport mechanism and structure of the high-affinity K+ nutrition pathway remain unknown. Here we use expression cloning to isolate a complementary DNA encoding a membrane protein (HKT1) from wheat roots which confers the ability to take up K+. The substrate affinity, saturation and cation selectivity of HKT1 correspond to hallmark properties of classical high-affinity K+ uptake in plants. The transport mechanism of HKT1 uses K(+)-H+ co-uptake. Expression of HKT1 is localized to specific root and leaf regions which represent primary sites for K+ uptake in plants. HKT1 is important for plant nutrition and could possibly contribute to environmental alkali metal toxicities.

PMID: 8065452

2000

6.555

0.0

. 2000, 122:1249-1259

The Arabidopsis HKT1 gene homolog mediates inward Na+ currents in Xenopus laevis Oocytes and Na+ uptake in Saccharomyces cerevisiae

Bioscience Center, Nagoya University, Nagoya, 464-8601, Japan. uozumi@agr.nagoya-u.ac.jp

The Na(+)-K(+) co-transporter HKT1, first isolated from wheat, mediates high-affinity K(+) uptake. The function of HKT1 in plants, however, remains to be elucidated, and the isolation of HKT1 homologs from Arabidopsis would further studies of the roles of HKT1 genes in plants. We report here the isolation of a cDNA homologous to HKT1 from Arabidopsis (AtHKT1) and the characterization of its mode of ion transport in heterologous systems. The deduced amino acid sequence of AtHKT1 is 41% identical to that of HKT1, and the hydropathy profiles are very similar. AtHKT1 is expressed in roots and, to a lesser extent, in other tissues. Interestingly, we found that the ion transport properties of AtHKT1 are significantly different from the wheat counterpart. As detected by electrophysiological measurements, AtHKT1 functioned as a selective Na(+) uptake transporter in Xenopus laevis oocytes, and the presence of external K(+) did not affect the AtHKT1-mediated ion conductance (unlike that of HKT1). When expressed in Saccharomyces cerevisiae, AtHKT1 inhibited growth of the yeast in a medium containing high levels of Na(+), which correlates to the large inward Na(+) currents found in the oocytes. Furthermore, in contrast to HKT1, AtHKT1 did not complement the growth of yeast cells deficient in K(+) uptake when cultured in K(+)-limiting medium. However, expression of AtHKT1 did rescue Escherichia coli mutants carrying deletions in K(+) transporters. The rescue was associated with a less than 2-fold stimulation of K(+) uptake into K(+)-depleted cells. These data demonstrate that AtHKT1 differs in its transport properties from the wheat HKT1, and that AtHKT1 can mediate Na(+) and, to a small degree, K(+) transport in heterologous expression systems.

PMID: 10759522

2007

5.242

0.0

. 2007, 58(15-16):4387-4395 DOI:10.1093/jxb/erm306

Cloning and functional comparison of a high-affinity K+ transporter gene PhaHKT1 of salt-tolerant and salt-sensitive reed plants

Asian Natural Environmental Science Center (ANESC), The University of Tokyo, 1-1-1 Midori-cho, Nishitokyo-shi, Tokyo 188-0002, Japan.

To understand the mechanisms of ion homeostasis in salt-tolerant and salt-sensitive plants, cDNAs for a high-affinity K(+) transporter PhaHKT1 were isolated from salt-sensitive (Utsunomiya) and salt-tolerant (Nanpi, Enchi) reed plants. A cDNA of Utsunomiya (PhaHKT1-u) contained two insertions in the region corresponding to the first and second introns of the PhaHKT1 gene, which resulted in a sequence 141 amino acid residues shorter than that of Nanpi. Expression of PhaHKT1 mRNA was detected in the roots of Nanpi and Enchi plants under K(+) starvation conditions and also under Na(+) treatment conditions, whereas it was only slightly detected in the roots of Utsunomiya plants under each of these conditions. In the upper parts, PhaHKT1 expression was detected in the Utsunomiya plants, and two signals were obtained in the Nanpi and Enchi plants under all and K(+) starvation conditions, respectively. Yeasts expressing the PhaHKT1 of Nanpi (PhaHKT1-n) or the PhaHKT1 of Enchi (PhaHKT1-e) grew better in the presence of NaCl than yeast expressing PhaHKT1-u. Furthermore, yeast expressing a chimeric cDNA containing the 5' region of the Utsunomiya gene and the 3' region of the Nanpi gene had partial salt tolerance, and yeast expressing a chimeric cDNA containing the 5' region of the Nanpi gene and the 3' region of the Utsunomiya gene had a reduced ability to take up ions. These results suggest that PhaHKT1 plays an important role in the acquisition of K(+) and maintenance of ion balance under saline conditions.

PMID: 18182440

2008

2.881

0.0

. 2008, 280(5):437-452 DOI:10.1007/s00438-008-0377-7

KT/HAK/KUP potassium transporters gene family and their whole-life cycle expression profile in rice (Oryza sativa)

1.Huazhong Agricultural University National Key Laboratory of Crop Genetic Improvement, National Center of Plant Gene Research (Wuhan) Wuhan 430070 China

KT/HAK/KUP potassium transporter protein-encoding genes constitute a large family in the plant kingdom. The KT/HAK/KUP family is important for various physiological processes of plant life. In this study, we identified 27 potential KT/HAK/KUP family genes in rice ( Oryza sativa ) by database searching. Analysis of these KT/HAK/KUP family members identified three conserved motifs with unknown functions, and 11–15 trans -membrane segments, most of which are conserved. A total of 144 putative cis -elements were found in the 2 kb upstream region of these genes, of which a Ca 2+ -responsive cis -element, two light-responsive cis -elements, and a circadian-regulated cis -element were identified in the majority of the members, suggesting regulation of these genes by these signals. A comprehensive expression analysis of these genes was performed using data from microarrays hybridized with RNA samples of 27 tissues covering the entire life cycle from three rice genotypes, Minghui 63, Zhenshan 97, and Shanyou 63. We identified preferential expression of two OsHAK genes in stamen at 1 day before flowering compared with all the other tissues. OsHAK genes were also found to be differentially upregulated or downregulated in rice seedlings subjected to treatments with three hormones. These results would be very useful for elucidating the roles of these genes in growth, development, and stress response of the rice plant.

2003

3.518

0.0

. 2003, 52(5):967-980 DOI:10.1023/A:1025445612244

Expression of the cation transporter McHKT1 in a halophyte

1.Department of Plant Sciences 2.Universidad Nacional Autónoma de México 3.University of Arizona 4.Universit?t Bielefeld 5.Université Joseph Fourier 6.University of Arizona 7.University of Arizona

From the ice plant, Mesembryanthemum crystallinum , McHKT1 was isolated encoding a protein 41–61% identical to other plant HKT1-like sequences previously described as potassium or sodium/potassium transporters. McHKT1 acts as a potassium transporter in yeast with specificity similar to that of wheat HKT1. In Xenopus oocytes it transports cations with a specificity Rb + > Cs + > [K + = Na + = Li + ]. McHKT1 is exclusively localized to the plasma membrane. The isoform isolated is most highly expressed in leaves and is present in stems, flowers and seed pods but absent from the root where, according to immunological data, a second isoform exists which does not cross-hybridize with the leaf form in RNA blots at high stringency. McHKT1 transcript amounts increase during the first 6–10 h of stress and then decline to pre-stress levels with kinetics reminiscent of the initial influx of sodium into this halophyte. Immunocytological localization showed strong signals in the leaf vasculature and surrounding mesophyll cells but low-intensity signals are also detected in other cell types. In roots, McHKT is mainly confined to endodermis and stele. Possible functions of McHKT1 in ion homeostasis in the halophytic ice plant are discussed.

2001

6.555

0.0

. 2001, 127:283-294

Characterization of two HKT1 homologues from Eucalyptus camaldulensis that display intrinsic osmosensing capability

CSIRO Plant Industry Horticulture Unit, G.P.O. Box 350, Glen Osmond, South Australia 5064, Australia.

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.

PMID: 11553756

2005

0.0

2011

0.0

2010

0.0

2002

0.0

. 2002, 32(2):139-149

A role for HKT1 in sodium uptake by wheat roots

IACR Long Ashton, Crop Performance and Improvement Division, Long Ashton, Bristol, BS41 9AF, UK. sophie.lauren@bbsrc.ac.uk

The high affinity potassium transporter, HKT1 from wheat was introduced into Florida wheat in sense and antisense orientation under control of a ubiquitin promoter. Ten transgenic lines expressing the transgene were identified and two of these showed strong down-regulation of the native HKT1 transcript. One line (271) was expressing the antisense construct and the other (223) was expressing a truncated sense construct. The two lines were examined further for phenotype relating to cation transport. Membrane depolarisations were measured in low (0.1 mm) K+ and high (100 mm) NaCl. Under these conditions there was no difference between line 271 and the control at low K+, but at high Na+ there was a rapid depolarisation that was significantly larger in control plants. 22Na uptake was measured in this line and there was a significant decrease in uptake at 100 mm NaCl in the transgenic line when compared with the control. The two transgenic lines were grown at high NaCl (200 mm) and analysed for growth and root sodium content. Lines 271 and 223 showed enhanced growth under salinity when compared with the control and had lower sodium in the root. Secondary ion mass spectrometry (SIMS) analysis of transverse sections of the root showed that Na+ and K+ were strongly localised to stelar regions when compared with other ions, and that the Na+ : K+ ratios were reduced in salt-stressed transgenic tissue when compared with the control.

PMID: 12383080

... 早期研究认为,HKT1蛋白是Na⁺吸收和运输的载体,降低HKT1的表达,可能会提高植物抗盐性,如Laurie等^[15]研究发现,表达反义HKT1基因的小麦植株较野生型耐盐胁迫能力更强 ...

2001

0.0

. 2001, 27(2):129-138

Two types of HKT transporters with different properties of Na+ and K+ transport in Oryza sativa

Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama-cho, Ikoma-shi, Nara 630-0101, Japan.

It is thought that Na+ and K+ homeostasis is crucial for salt-tolerance in plants. To better understand the Na+ and K+ homeostasis in important crop rice (Oryza sativa L.), a cDNA homologous to the wheat HKT1 encoding K+-Na+ symporter was isolated from japonica rice, cv Nipponbare (Ni-OsHKT1). We also isolated two cDNAs homologous to Ni-OsHKT1 from salt-tolerant indica rice, cv Pokkali (Po-OsHKT1, Po-OsHKT2). The predicted amino acid sequence of Ni-OsHKT1 shares 100% identity with Po-OsHKT1 and 91% identity with Po-OsHKT2, and they are 66-67% identical to wheat HKT1. Low-K+ conditions (less than 3 mM) induced the expression of all three OsHKT genes in roots, but mRNA accumulation was inhibited by the presence of 30 mM Na+. We further characterized the ion-transport properties of OsHKT1 and OsHKT2 using an expression system in the heterologous cells, yeast and Xenopus oocytes. OsHKT2 was capable of completely rescuing a K+-uptake deficiency mutation in yeast, whereas OsHKT1 was not under K+-limiting conditions. When OsHKTs were expressed in Na+-sensitive yeast, OsHKT1 rendered the cells more Na+-sensitive than did OsHKT2 in high NaCl conditions. The electrophysiological experiments for OsHKT1 expressed in Xenopus oocytes revealed that external Na+, but not K+, shifted the reversal potential toward depolarization. In contrast, for OsHKT2 either Na+ or K+ in the external solution shifted the reversal potential toward depolarization under the mixed Na+ and K+ containing solutions. These results suggest that two isoforms of HKT transporters, a Na+ transporter (OsHKT1) and a Na+- and K+-coupled transporter (OsHKT2), may act harmoniously in the salt tolerant indica rice.

PMID: 11489190

... Horie等^[16]比较耐盐水稻和盐敏感水稻时发现,抗盐性高的水稻HKT1基因的表达量在盐胁迫时降低,而盐敏感型水稻HKT1的表达量一直维持在很高水平 ...

2004

6.555

0.0

. 2004, 136(1):2500-2511

AtHKT1 facilitates Na+ homeostasis and K+ nutrition in planta

Center for Plant Environmental Stress Physiology, Purdue University, West Lafayette, IN 47907-2010, USA.

Genetic and physiological data establish that Arabidopsis AtHKT1 facilitates Na(+) homeostasis in planta and by this function modulates K(+) nutrient status. Mutations that disrupt AtHKT1 function suppress NaCl sensitivity of sos1-1 and sos2-2, as well as of sos3-1 seedlings grown in vitro and plants grown in controlled environmental conditions. hkt1 suppression of sos3-1 NaCl sensitivity is linked to higher Na(+) content in the shoot and lower content of the ion in the root, reducing the Na(+) imbalance between these organs that is caused by sos3-1. AtHKT1 transgene expression, driven by its innate promoter, increases NaCl but not LiCl or KCl sensitivity of wild-type (Col-0 gl1) or of sos3-1 seedlings. NaCl sensitivity induced by AtHKT1 transgene expression is linked to a lower K(+) to Na(+) ratio in the root. However, hkt1 mutations increase NaCl sensitivity of both seedlings in vitro and plants grown in controlled environmental conditions, which is correlated with a lower K(+) to Na(+) ratio in the shoot. These results establish that AtHKT1 is a focal determinant of Na(+) homeostasis in planta, as either positive or negative modulation of its function disturbs ion status that is manifested as salt sensitivity. K(+)-deficient growth of sos1-1, sos2-2, and sos3-1 seedlings is suppressed completely by hkt1-1. AtHKT1 transgene expression exacerbates K(+) deficiency of sos3-1 or wild-type seedlings. Together, these results indicate that AtHKT1 controls Na(+) homeostasis in planta and through this function regulates K(+) nutrient status.

PMID: 15347798

... Rus等^[17]研究发现拟南芥AtHKT1基因在sos3-1突变体的过量表达增强了突变体植株在低K⁺环境下对Na⁺的敏感性及植株的缺K⁺症状,AtHKT1基因可转运Na⁺进入细胞、调控根部Na⁺的吸收 ...

... 早期研究认为,AtHKT1基因的过量表达可增加植株的盐敏感性^[17],近期部分学者对该基因的作用有新解,认为AtHKT1基因可调节Na⁺在根和茎中的分配以及从茎到根部的再循环^[18,19,20],AtHKT1蛋白如果在拟南芥根部的中柱鞘及维管束过量表达,会增加Na⁺在根部木质部薄壁组织及皮层中滞留,减少Na⁺由根部转运至叶,从而降低叶片中Na⁺浓度,表明该基因在根部的过量表达可提高拟南芥植株的耐盐性,但如果由组成型35S启动子驱动AtHKT1基因在整个植株中的过量表达却导致了转基因植株的盐敏感性,说明AtHKT1基因的组织特异性表达与植株耐盐性关系密切^[24,25,26] ...

2002

3.582

0.0

. 2002, 531(2):157-161

Altered shoot/root Na+ distribution and bifurcating salt sensitivity in Arabidopsis by genetic disruption of the Na+ transporter AtHKT1

Division of Biological Sciences, Cell and Developmental Biology Section, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0116, USA.

Sodium (Na+) is toxic to most plants, but the molecular mechanisms of plant Na+ uptake and distribution remain largely unknown. Here we analyze Arabidopsis lines disrupted in the Na+ transporter AtHKT1. AtHKT1 is expressed in the root stele and leaf vasculature. athkt1 null plants exhibit lower root Na+ levels and are more salt resistant than wild-type in short-term root growth assays. In shoot tissues, however, athkt1 disruption produces higher Na+ levels, and athkt1 and athkt1/sos3 shoots are Na+-hypersensitive in long-term growth assays. Thus wild-type AtHKT1 controls root/shoot Na+ distribution and counteracts salt stress in leaves by reducing leaf Na+ accumulation.

PMID: 12417304

... ser等^[18]认为拟南芥AtHKT1基因参与调控Na⁺在根和地上部分的分配 ...

2003

9.205

0.0

. 2003, 22(9):2004-2014

Functional analysis of AtHKT1 in Arabidopsis shows that Na+ recirculation by the phloem is crucial for salt tolerance)J].

Biochimie et Physiologie Moléculaire des Plantes, UMR 5004, ENSA M INRA CNRS UMII and UMR Agronomie Ecophysiologie des Plantes sous Stress Environnementaux, INRA ENSA.M, 34060 Montpellier Cedex 2, France. berthom@ensam.inra.fr

Two allelic recessive mutations of Arabidopsis, sas2-1 and sas2-2, were identified as inducing sodium overaccumulation in shoots. The sas2 locus was found (by positional cloning) to correspond to the AtHKT1 gene. Expression in Xenopus oocytes revealed that the sas2-1 mutation did not affect the ionic selectivity of the transporter but strongly reduced the macro scopic (whole oocyte current) transport activity. In Arabidopsis, expression of AtHKT1 was shown to be restricted to the phloem tissues in all organs. The sas2-1 mutation strongly decreased Na(+) concentration in the phloem sap. It led to Na(+) overaccumulation in every aerial organ (except the stem), but to Na(+) underaccumulation in roots. The sas2 plants displayed increased sensitivity to NaCl, with reduced growth and even death under moderate salinity. The whole set of data indicates that AtHKT1 is involved in Na(+) recirculation from shoots to roots, probably by mediating Na(+) loading into the phloem sap in shoots and unloading in roots, this recirculation removing large amounts of Na(+) from the shoot and playing a crucial role in plant tolerance to salt.

PMID: 12727868

... Berthomieu等^[19]认为AtHKT1参与Na⁺通过韧皮部汁液从地上部分至根部的再循环过程,降低叶中Na⁺积累 ...

2005

0.0

. 2005, 44(6):928-938

Enhanced salt tolerance mediated by AtHKT1 transporter-induced Na+ unloading from xylem vessels to xylem parenchyma cells

Bioscience and Biotechnology Center, Nagoya University, Nagoya 464-8601, Japan.

AtHKT1 is a sodium (Na+) transporter that functions in mediating tolerance to salt stress. To investigate the membrane targeting of AtHKT1 and its expression at the translational level, antibodies were generated against peptides corresponding to the first pore of AtHKT1. Immunoelectron microscopy studies using anti-AtHKT1 antibodies demonstrate that AtHKT1 is targeted to the plasma membrane in xylem parenchyma cells in leaves. AtHKT1 expression in xylem parenchyma cells was also confirmed by AtHKT1 promoter-GUS reporter gene analyses. Interestingly, AtHKT1 disruption alleles caused large increases in the Na+ content of the xylem sap and conversely reduced the Na+ content of the phloem sap. The athkt1 mutant alleles had a smaller and inverse influence on the potassium (K+) content compared with the Na+ content of the xylem, suggesting that K+ transport may be indirectly affected. The expression of AtHKT1 was modulated not only by the concentrations of Na+ and K+ but also by the osmolality of non-ionic compounds. These findings show that AtHKT1 selectively unloads sodium directly from xylem vessels to xylem parenchyma cells. AtHKT1 mediates osmolality balance between xylem vessels and xylem parenchyma cells under saline conditions. Thus AtHKT1 reduces the sodium content in xylem vessels and leaves, thereby playing a central role in protecting plant leaves from salinity stress.

PMID: 16359386

... Sunarpi等^[20]认为在高盐环境下,AtHKT1基因调节Na⁺从根部木质部卸载 ...

2007

5.135

0.0

. 2007, 30(4):497-507

The Na+ transporter AtHKT1;1 controls retrieval of Na+ from the xylem in Arabidopsis

Department of Plant Sciences, Downing Street, Cambridge CB2 3EA, UK. romola.davenport@ageing.ox.ac.uk

HKT-type transporters appear to play key roles in Na(+) accumulation and salt sensitivity in plants. In Arabidopsis HKT1;1 has been proposed to influx Na(+) into roots, recirculate Na(+) in the phloem and control root : shoot allocation of Na(+). We tested these hypotheses using (22)Na(+) flux measurements and ion accumulation assays in an hkt1;1 mutant and demonstrated that AtHKT1;1 contributes to the control of both root accumulation of Na(+) and retrieval of Na(+) from the xylem, but is not involved in root influx or recirculation in the phloem. Mathematical modelling indicated that the effects of the hkt1;1 mutation on root accumulation and xylem retrieval were independent. Although AtHKT1;1 has been implicated in regulation of K(+) transport and the hkt1;1 mutant showed altered net K(+) accumulation, (86)Rb(+) uptake was unaffected by the hkt1;1 mutation. The hkt1;1 mutation has been shown previously to rescue growth of the sos1 mutant on low K(+); however, HKT1;1 knockout did not alter K(+) or (86)Rb(+) accumulation in sos1.

PMID: 17324235

... 特别是最近的研究又发现,AtHKT1基因既不调控Na⁺从地上部到根部的再循环,也不调节Na⁺以内流的形式进入根部,而是将Na⁺直接滞留在根的木质部中,加载Na⁺进入根部液泡,从而降低Na⁺从根到茎的运输^{[21,22,23,24,25,26]} ...

2008

25.962

0.0

. 2008, 59:651-681 DOI:10.1146/annurev.arplant.59.032607.092911

Mechanisms of salinity tolerance

CSIRO Plant Industry, Canberra, ACT, Australia. rana.munns@csiro.au

The physiological and molecular mechanisms of tolerance to osmotic and ionic components of salinity stress are reviewed at the cellular, organ, and whole-plant level. Plant growth responds to salinity in two phases: a rapid, osmotic phase that inhibits growth of young leaves, and a slower, ionic phase that accelerates senescence of mature leaves. Plant adaptations to salinity are of three distinct types: osmotic stress tolerance, Na(+) or Cl() exclusion, and the tolerance of tissue to accumulated Na(+) or Cl(). Our understanding of the role of the HKT gene family in Na(+) exclusion from leaves is increasing, as is the understanding of the molecular bases for many other transport processes at the cellular level. However, we have a limited molecular understanding of the overall control of Na(+) accumulation and of osmotic stress tolerance at the whole-plant level. Molecular genetics and functional genomics provide a new opportunity to synthesize molecular and physiological knowledge to improve the salinity tolerance of plants relevant to food production and environmental sustainability.

PMID: 18444910

2009

11.808

0.0

. 2009, 14(12):660-668 DOI:10.1016/j.tplants.2009.08.009

HKT transporter-mediated salinity resistance mechanisms in Arabidopsis and monocot crop plants

The salinization of irrigated lands is increasingly detrimental to plant biomass production and agricultural productivity, as most plant species are sensitive to high concentrations of sodium (Na + ), which causes combined Na + toxicity and osmotic stress. Plants have multiple Na + -transport systems to circumvent Na + toxicity. Essential physiological functions of major Na + transporters and their mechanisms mediating salinity resistance have been identified in Arabidopsis , including the AtSOS1, AtNHX and AtHKT1;1 transporters. As we discuss here, recent studies have demonstrated that a class of xylem–parenchyma-expressed Na + -permeable plant HKT transporters represent a primary mechanism mediating salt tolerance and Na + exclusion from leaves in Arabidopsis , and that major salt-tolerance quantitative trait loci in monocot crop plants are also based on this HKT-mediated mechanism.

2010

5.135

0.0

. 2010, 33(4):612-626 DOI:10.1111/j.1365-3040.2009.02086.x

Na+ transport in glycophytic plants: what we know and would like to know

Australian Centre for Plant Functional Genomics, University of Adelaide, Glen Osmond, SA, Australia. darren.plett@acpfg.com.au

Soil salinity decreases the growth rate of plants and can severely limit the productivity of crop plants. The ability to tolerate salinity stress differs widely between species of plants as well as within species. As an important component of salinity tolerance, a better understanding of the mechanisms of Na(+) transport will assist in the development of plants with improved salinity tolerance and, importantly, might lead to increased yields from crop plants growing in challenging environments. This review summarizes the current understanding of the components of Na(+) transport in glycophytic plants, including those at the soil to root interface, transport of Na(+) to the xylem, control of Na(+) loading in the stele and partitioning of the accumulated Na(+) within the shoot and individual cells. Using this knowledge, strategies to modify Na(+) transport and engineer plant salinity tolerance, as well as areas of research which merit particular attention in order to further improve the understanding of salinity tolerance in plants, are discussed.

PMID: 19968828

2009

0.0

. 2009, 21(7):2163-2178 DOI:10.1105/tpc.108.064568

Shoot Na+ exclusion and increased salinity tolerance engineered by cell type-specific alteration of Na+ transport in Arabidopsis

Department of Plant Sciences, University of Cambridge, Cambridge CB2 3EA, United Kingdom.

Soil salinity affects large areas of cultivated land, causing significant reductions in crop yield globally. The Na+ toxicity of many crop plants is correlated with overaccumulation of Na+ in the shoot. We have previously suggested that the engineering of Na+ exclusion from the shoot could be achieved through an alteration of plasma membrane Na+ transport processes in the root, if these alterations were cell type specific. Here, it is shown that expression of the Na+ transporter HKT1;1 in the mature root stele of Arabidopsis thaliana decreases Na+ accumulation in the shoot by 37 to 64%. The expression of HKT1;1 specifically in the mature root stele is achieved using an enhancer trap expression system for specific and strong overexpression. The effect in the shoot is caused by the increased influx, mediated by HKT1;1, of Na+ into stelar root cells, which is demonstrated in planta and leads to a reduction of root-to-shoot transfer of Na+. Plants with reduced shoot Na+ also have increased salinity tolerance. By contrast, plants constitutively expressing HKT1;1 driven by the cauliflower mosaic virus 35S promoter accumulated high shoot Na+ and grew poorly. Our results demonstrate that the modification of a specific Na+ transport process in specific cell types can reduce shoot Na+ accumulation, an important component of salinity tolerance of many higher plants.

PMID: 19584143

2009

0.0

. 2009, 21(7):1875- DOI:10.1105/tpc.109.210710

Targeted overexpression of a sodium transporter in the root stele increases salinity tolerance

kfarquharson@aspb.org

PMID: 19602620

2012

0.0

... 说明同一物种中该基因保守,但不同物种间差异明显,这与其他研究者对不同基因或不同物种同源性分析时的结论是一致的,即属内同源性高,属间相对低^[27,28,29],可见高亲和性K⁺载体蛋白在进化上也存在多样性 ...

2012

0.0

2012

0.0

2006

0.0

... 王景艳等^[30]认为植物通过离子外排和区域化降低Na⁺的毒害与植物跨膜运输蛋白有密切关系,AtHKT1蛋白疏水性及跨膜性分析表明,该蛋白有10个跨膜区,是疏水性蛋白,符合载体类跨膜运输蛋白特点,推测其与钾和钠离子的转运相关 ...