OsbZIP72 Is Involved in Transcriptional Gene-Regulation Pathway of Abscisic Acid Signal Transduction by Activating Rice High-Affinity Potassium Transporter OsHKT1;1

We created CRISPR-Cas9 knock-out and overexpressing OsbZIP72 transgenic rice plants to gain a better understanding of the role and molecular mechanism of OsbZIP72 gene in stress tolerance,which has remained largely elusive.OsbZIP72 was expressed and integrated into rice transgenic plant genomes,and the OsbZIP72 transcript in overexpression lines was elicited by salinity,abscisic acid(ABA)and drought stresses.OsbZIP72 overexpressing plants showed higher tolerance to drought and salinity stresses,while knock-out transgenic lines showed higher sensitivity to these stresses.The differentially expressed genes(DEGs)from RNA-sequencing data encompassed several abiotic stress genes,and the functional classification of these DEGs demonstrated the robust transcriptome diversity in OsbZIP72.Yeast one-hybrid,along with luciferase assay,indicated that OsbZIP72 acted as a transcriptional initiator.Remarkably,electrophoresis mobility assay revealed that OsbZIP72 bound directly to the ABAresponsive element in the OsHKT1;1 promoter region and activated its transcription.Overall,our findings revealed that OsbZIP72 can act as a transcriptional modulator with the ability to induce the expression of OsHKT1;1 in response to environmental stress through an ABA-dependent regulatory pathway,indicating that OsbZIP72 can play a crucial role in the ABA-mediated salt and drought tolerance pathway in rice.

Potassium nutrition of maize:Uptake,transport,utilization,and role in stress tolerance

Potassium(K) is an essential macronutrient for plant growth and development and influences yield and quality of agricultural crops.Maize(Zea mays) is one of the most widely distributed crops worldwide.In China,although maize consumes a large amount of K fertilizer,the K uptake/utilization efficiency(KUE)of maize cultivars is relatively low.Elucidation of KUE mechanisms and development of maize cultivars with higher KUE are needed.Maize KUE is determined by K+uptake,transport,and remobilization,which depend on a variety of K+channels and transporters.We review basic information about K+channels and transporters in maize,their functions and regulation,and the roles of K+in nitrogen transport,sugar transport,and salt tolerance.We discuss challenges and prospects for maize KUE improvement.

Analgesic effect of intrathecal bumetanide is accompanied by changes in spinal sodium-potassium-chloride co-transporter 1 and potassium-chloride co-transporter 2 expression in a rat model of incisional pain

Accumulating evidence has demonstrated that the sodium-potassium-chloride co-transporter 1 and potassium-chloride co-transporter 2 have a role in the modulation of pain transmission at the spinal level through chloride regulation in the pain pathway and by effecting neuronal excitability and pain sensitization. The present study aimed to investigate the analgesic effect of the speciifc sodium-potassium-chloride co-transporter 1 inhibitor bumetanide, and the change in spinal sodium-potassium-chloride co-transporter 1 and potassium-chloride co-transporter 2 expression in a rat model of incisional pain. Results showed that intrathecal bumetanide could decrease cumulative pain scores, and could increase thermal and mechanical pain thresholds in a rat model of incisional pain. Sodium-potassium-chloride co-transporter 1 expression in-creased in neurons from dorsal root ganglion and the deep laminae of the ipsilateral dorsal horn following incision. By contrast, potassium-chloride co-transporter 2 expression decreased in neurons of the deep laminae from the ipsilateral dorsal horn. These ifndings suggest that spinal sodium-potassium-chloride co-transporter 1 expression was up-regulated and spinal potassi-um-chloride co-transporter 2 expression was down-regulated following incision. Intrathecal bumetanide has analgesic effects on incisional pain through inhibition of sodium-potassi-um-chloride co-transporter 1.

Potassium transporter OsHAK9 regulates seed germination under salt stress by preventing gibberellin degradation through mediating OsGA2ox7 in rice

Soil salinity has a major impact on rice seed germination,severely limiting rice production.Herein,a rice germination defective mutant under salt stress(gdss)was identified by using chemical mutagenesis.The GDSS gene was detected via MutMap and shown to encode potassium transporter OsHAK9.Phenotypic analysis of complementation and mutant lines demonstrated that OsHAK9 was an essential regulator responsible for seed germination under salt stress.OsHAK9 is highly expressed in germinating seed embryos.Ion contents and non-invasive micro-test technology results showed that OsHAK9 restricted K^(+)efflux in salt-exposed germinating seeds for the balance of K^(+)/Na^(+).Disruption of OsHAK9 significantly reduced gibberellin 4(GA4)levels,and the germination defective phenotype of oshak9a was partly rescued by exogenous GA_(3)treatment under salt stress.RNA sequencing(RNA-seq)and real-time quantitative polymerase chain reaction analysis demonstrated that the disruption of OsHAK9 improved the GA-deactivated gene OsGA2ox7 expression in germinating seeds under salt stress,and the expression of OsGA2ox7 was significantly inhibited by salt stress.Null mutants of OsGA2ox7 created using clustered,regularly interspaced,short palindromic repeat(CRISPR)/CRISPR-associated nuclease 9 approach displayed a dramatically increased seed germination ability under salt stress.Overall,our results highlight that OsHAK9 regulates seed germination performance under salt stress involving preventing GA degradation by mediating OsGA2ox7,which provides a novel clue about the relationship between GA and OsHAKs in rice.

Influences of external nutrient conditions on the transcript levels of a nitrate transporter gene in Skeletonema costatum

To verify the feasibility of high-affinity nitrate transporter gene （Nrt2） as an indicator of nitrogen status, changes in the transcript levels of transcripts associated with phosphate starvation and different nitrate concentrations were studied using real-time quantitative reverse-transcription PCR （QRT-PCR） technology in batch cultures of Skeletonema costatum. The results show that compared with P-replete condition, P starvation could reduce the Nrt2 transcript levels apparently. Nrt2 transcript levels had a significant negative linear correlation with nitrate concentrations below 40 pmol/L. The results of 48 h short-term incubation experiment under different nitrate concentrations confirmed this correlation, and the following regression equation is built： y = -3.305x ＋ 98.95, R2 = 0.988, where x represents nitrate concentrations （〈40 btmol/L） and y represents the Nrt2 transcript levels.

Identification of the HAK gene family reveals their critical response to potassium regulation during adventitious root formation in apple rootstock

Adventitious root formation is a bottleneck during vegetative proliferation.Potassium(K^(+))is an essential macronutrient for plants.K^(+)accumulation from the soil and its distribution to the different plant organs is mediated by K^(+)transporters named K^(+)transporter(KT),K^(+)uptake(KUP),or high-affinity K^(+)(HAK).This study aimed to identify members of the HAK gene family in apples and to characterize the effects of K^(+)supply on adventitious root formation and on the expression of HAK genes and the genes that putatively control auxin transport,signaling,and cell fate during adventitious root formation.In this study,34 HAK genes(MdHAKs)were identified in the apple(Malus×domestica‘Golden Delicious’)genome.A phylogenetic analysis divided MdHAKs into four clusters(Ⅰ,Ⅱ,Ⅲ,andⅣ),comprising 16,1,4,and 13 genes,respectively.The syntenic relationships revealed that 62.5%of the total MdHAK genes arise from genomic duplication events.Chromosome location,domain structure,motif analysis,and physico-chemical characteristics were subsequently investigated.Furthermore,the application of K^(+)indicated the emergence of adventitious roots at 8 d and produced more adventitious roots at 16 d than the K^(+)-free control(CK)treatment.In addition,various MdHAKs showed root-specific expression in B9 apple rootstock stem cuttings and enhanced expression during the initiation and emergence stages of adventitious root formation in response to K^(+)treatment.Additionally,K^(+)treatment enhanced the expression levels of MdPIN1,MdPIN2,and MdAUX1.Further data indicated that a higher expression of MdWOX11,MdLBD16,and MdLBD29 and of cell cycle-related genes contributed to the auxin-stimulated adventitious root formation in response to K^(+).

Changes in urinary excretion of water and sodium transporters during amiloride and bendroflumethiazide treatment

AIM:To quantify changes in urinary excretion of aquaporin2 water channels(u-AQP2),the sodiumpotassium-chloride co-transporter(u-NKCC2) and the epithelial sodium channels(u-ENa C) during treatment with bendroflumethiazide(BFTZ),amiloride and placebo.METHODS:In a randomized,double-blinded,placebocontrolled,3-way crossover study we examined 23 healthy subjects on a standardized diet and fluid intake.The subjects were treated with amiloride 5 mg,BFTZ 1.25 mg or placebo twice a day for 4.5 d before each examination day.On the examination day,glomerular filtration rate was measured by the constant infusion clearance technique with 51Cr-EDTA as reference substance.To estimate the changes in water transport via AQP2 and sodium transport via NKCC2 and ENa C,u-NKCC2,the gamma fraction of ENa C(u-ENa Cγ),andu-AQP2 were measured at baseline and after infusion with 3% hypertonic saline.U-NKCC2,u-ENa Cγ,u-AQP2 and plasma concentrations of vasopressin(p-AVP),renin(PRC),angiotensin Ⅱ(p-ANG Ⅱ) and aldosterone(p-Aldo) were measured,by radioimmunoassay.Central blood pressure was estimated by applanation tonometry and body fluid volumes were estimated by bio-impedance spectroscopy.General linear model with repeated measures or related samples Friedman's two-way analysis was used to compare differences.Post hoc Bonferroni correction was used for multiple comparisons of post infusion periods to baseline within each treatment group.RESULTS:At baseline there were no differences in u-NKCC2,u-ENa Cγ and u-AQP2.PRC,p-Ang Ⅱ and p-Aldo were increased during active treatments(P < 0.001).After hypertonic saline,u-NKCC2 increased during amiloride(6% ± 34%;P = 0.081) and increased significantly during placebo(17% ± 24%;P = 0.010).U-AQP2 increased significantly during amiloride(31% ± 22%;P < 0.001) and placebo(34% ± 27%;P < 0.001),while u-NKCC2 and u-AQP2 did not change significantly during BFTZ(-7% ± 28%;P = 0.257 and 5% ± 16%;P = 0.261).U-ENa Cγ increased in all three groups(P < 0.050).PRC,AngⅡ and p-Aldo decreased to the same extent,while AVP increased,but to a smaller degree during BFTZ(P = 0.048).c DBP decreased significantly during BFTZ(P < 0.001),but not during amiloride or placebo.There were no significant differences in body fluid volumes.CONCLUSION:After hypertonic saline,u-NKCC2 and u-AQP2 increased during amiloride,but not during BFTZ.Lower p-AVP during BFTZ potentially caused less stimulation of NKCC2 and AQP2 and subsequent lower reabsorption of water and sodium.

杨树KT、HAK、KUP基因家族鉴定及钾肥处理对杨树生长的影响

KT、HAK、KUP基因家族是植物进行K^(+)转运的最大蛋白系统。以毛果杨(Populus trichocarpa Torr.&Gray)全基因组数据为基础,利用生物信息学方法对杨树KT、HAK、KUP家族进行了全基因组鉴定,并在毛果杨全基因组中鉴定出20个KT、HAK、KUP家族成员。理化性质预测分析表明:KT、HAK、KUP基因家族成员均为疏水性蛋白,等电点在5.30~9.16;亚细胞定位预测显示家族成员蛋白集中在细胞质膜上。应用拟南芥和杨树构建系统进化树显示,KT、HAK、KUP基因家族可分为5个亚家族。基因结构及基序(motif)分析表明,KT、HAK、KUP基因进化过程相对保守。顺式作用元件分析表明,KT、HAK、KUP基因家族成员含有诸多与激素、逆境胁迫的响应元件。杨树不同钾离子浓度处理下,植株的净生长情况呈现了显著的差异,说明钾元素对杨树生长影响较大。

Potassium sulphate induces resistance of rice against the rootknot nematode Meloidogyne graminicola

Potassium(K),an important nutrient element,can improve the stress resistance/tolerance of crops.The application of K in resisting plant-parasitic nematodes shows that the K treatment can reduce the occurrence of nematode diseases and increase crop yield.However,data on K_(2)SO_(4)induced rice resistance against the root-knot nematode Meloidogyne graminicola are still lacking.In this work,K_(2)SO_(4)treatment reduced galls and nematodes in rice plants and delayed the development of nematodes.Rather than affecting the attractiveness of roots to nematodes and the morphological phenotype of giant cells at feeding sites,such an effect is achieved by rapidly priming hydrogen peroxide(H_(2)O_(2))accumulation and increasing callose deposition.Meanwhile,galls and nematodes in rice roots were more in the potassium channel OsAKT11 and transporter OsHAK5 gene-deficient plants than in wild-type,while the K_(2)SO_(4)-induced resistance showed weaker in the defective plants.In addition,during the process of nematode infection,the expression of jasmonic acid(JA)/ethylene(ET)/brassinolide(BR)signaling pathway-related genes and pathogenesis-related(PR)genes OsPR1 a/OsPR1 b was up-regulated in rice after K_(2)SO_(4)treatment.In conclusion,K_(2)SO_(4)induced rice resistance against M.graminicola.The mechanism of inducing resistance was to prime the basal defense and required the participation of the K^(+)channel and transporter in rice.These laid a foundation for further study on the mechanism of rice defense against nematodes and the rational use of potassium fertilizer on improving rice resistance against nematodes in the field.

Migration-associated secretion of melanoma inhibitory activity at the cell rear is supported by KCa3.1 potassium channels

恶意的黑瘤，由侵略本地生长和转移的早形成描绘了，是皮癌症的最好攻击的类型。黑瘤禁止的活动(MIA ) ，由恶意的黑瘤房间藏匿了，与房间粘附受体， integrins 伪 4 尾 1 和伪 5 尾 1，便于的房间分开和转移的支持的形成交往。在现在的学习，我们证明那 MIA 分泌物被限制到移植房间的后面的目的，当在非移居的房间 MIA 在肌动朊外皮积累时。MIA 蛋白质包括上衣蛋白质建筑群拿一条常规能分泌的小径我(COPI )- 并且上衣蛋白质建筑群 II (COPII ) 依赖者蛋白质运输到房间圆周，在它的最后的版本取决于细胞内部的 Ca2+ 离子的地方。有趣地，激活 Ca2+ 的 K+ 隧道，亚科 N，成员 4 (KCa3.1 ) ，知道在移植房间的后面的结束活跃，被发现支持 MIA 分泌物。分泌物被特定的 KCa3.1 隧道禁止者 TRAM-34 并且由隧道的主导否定的异种的表示减少。在摘要，我们阐明了到房间尾部并且也的 MIA 蛋白质的联系迁居的运输揭示了 KCa3.1 钾隧道由支持房间移植的新机制。

谷子HAK/KUP/KT钾转运蛋白家族全基因组鉴定及其对低钾和高盐胁迫的响应

KT/HAK/KUP(HAK)家族是植物中最丰富的钾转运体家族,对植物的生长和环境适应具有重要作用。谷子是抗逆耐瘠研究的模式植物,然而,谷子中HAK家族缺乏系统研究。本研究基于基因组序列信息,鉴定出29个谷子HAK基因(SiHAKs),并对该家族成员的基本特征、蛋白结构、染色体定位、基因复制、表达模式和逆境响应等方面进行了系统分析。结果显示,(1)SiHAKs分为5个进化簇(Cluster I~Cluster V),成员数量分别为11、9、3、3和3。基因结构和蛋白保守基序分析表明,谷子HAK家族具有较高的保守性,不同Cluster的保守性依次为:ClusterIII=Cluster V>Cluster II>Cluster I>Cluster IV。(2)串联复制是SiHAKs扩增的主要原因,15个SiHAKs位于串联重复中。(3)171个转录因子可能结合到不同SiHAKs的启动子上,这些转录因子包含ERF、NAC、MYB和WRKY等家族中的大量成员,可能授予了SiHAKs对非生物胁迫多样的响应机制。(4)基因表达聚类将SiHAKs分成3组:GroupI、Group II和Group III,多数SiHAKs在张谷和豫谷1号2个品种中的表达模式具有一致性;不同Cluster表达水平总体表现为:Cluster III>Cluster V>Cluster II>Cluster I>Cluster IV。(5)根系中表达水平较高的11个SiHAKs用来检测对低钾和高盐胁迫的响应。在低钾胁迫后,8个SiHAKs的表达水平显著升高,1个SiHAK显著降低,2个SiHAKs变化不明显;而高盐胁迫后,3个SiHAKs的表达水平显著升高,2个SiHAKs显著降低,其余6个SiHAKs变化不明显。SiHAK15受到低钾和高盐胁迫的响应最为强烈,其表达量分别为对照的151倍和22倍。(6)基因表达谱的差异反映出不同Cluster间SiHAKs的功能差异。ClusterI主要在根系中表达,可能参与谷子根系K+的吸收;ClusterII不具有组织表达特异性,推测其参与K+的吸收、转运和生长发育等多个生物过程;Cluster III受到低钾和高盐2种胁迫的诱导,显示出维持谷子K+/Na+平衡和抵御盐胁迫的潜在作用;ClusterIV在被检测的多个组织中几乎不表达;ClusterV不同成员对低钾和高盐胁迫的响应存在差异,可能发生了功能分化。研究结果不仅为深入解析谷子HAK家族的功能奠定了基础,而且为植物中钾高效利用和耐盐机制的研究提供了重要线索。

SbHKT1;4, a member of the high‐affinity potassium transporter gene family from Sorghum bicolor, functions to maintain optimal Na^+/K^+ balance under Na^+ stress

In halophytic plants, the high-affinity potassium transporter HKT gene family can selectively uptake K＋ in the presence of toxic concentrations of Na＋. This has so far not been well examined in glycophytic crops. Here, we report the characterization of SbHKTI;4, a member of the HKT gene family from Sorghum bicolor. Upon Na＋ stress, SbHKT1;4 expression was more strongly upregulated in salt-tolerant sorghum accession, correlating with a better balanced Na＋/ K＋ ratio and enhanced plant growth. Heterogeneous expression analyses in mutants of Saccharomyces cerevisiae and Arabidopsis thaliana indicated that overexpressing SbHKT1;4 resulted in hypersensitivity to Na＋ stress, and such hypersensitivity could be alleviated with the supply of elevated levels of K＋, implicating that SbHKT1;4 may mediate K＋ uptake in the presence of excessive Na＋. Further electrophysiological evidence demonstrated that SbHKT1;4 could transport Na＋ and K＋ when expressed in Xenopus laevis oocytes. The relevance of the finding that SbHKTI;4 functions to maintain optimal Na＋/K＋ balance under Na＋ stress to the breeding of salt-tolerant glycophytic crops is discussed.

大豆钾营养及其分子调控机制研究进展

钾元素对大豆的产量、品质以及抗逆性均有重要影响。土壤中富含钾元素,但大部分钾不能被根系直接吸收利用,导致植物缺钾。生产中需要额外施入钾肥满足大豆生长发育所需钾素,而过量的钾肥使用又加剧了环境污染。解决这一两难困局的重要举措在于提高大豆对钾素的吸收利用效率。因此,掌握大豆吸收利用钾素的规律并解析其背后的分子遗传机制是实现大豆钾高效的重要前提。本文综述了国内外研究者对大豆不同生长发育时期钾素的吸收、积累及转运再分配规律相关研究数据,重点对大豆钾营养高效分子遗传机制方面的研究进展进行了总结,同时针对该领域的研究现状提出了未来值得研究和关注的科学问题。

萝卜HAK/KUP/KT基因家族鉴定与表达特性分析

钾元素是植物生长发育过程中必需的主要矿质营养元素之一,对作物的产量和品质有决定性影响,细胞内K+含量水平在很大程度上受K+转运蛋白控制。通过生物信息学方法从全基因组水平鉴定出萝卜K^(+)转运蛋白HAK/KUP/KT基因家族成员,并对其基因结构、蛋白质特性、保守基序、染色体定位、启动子顺式作用元件、系统进化及表达特性等进行分析。结果表明,鉴定出的17个萝卜HAK/KUP/KT基因不均等地分布在萝卜6条染色体及Scaffold00840上,根据与拟南芥的同源关系将其命名为RsHAK1~RsHAK17;RsHAKs基因结构、保守基序、蛋白质理化特性等均具有高度保守性,启动子区域存在大量与环境因素、植物激素、逆境胁迫应答等有关的顺式作用元件;系统进化分析结果显示,17个RsHAKs基因聚为4个亚家族,全基因组复制事件是RsHAKs基因扩张的主要驱动力。转录组和qRT-PCR表达分析结果表明,除RsHAK5仅在萝卜根部表达外,其他RsHAKs在萝卜各器官及发育过程中均有特异性表达,且在高钾渗透胁迫下在叶片中相对表达量显著上调,RsHAK3、RsHAK9、RsHAK11和RsHAK12在根部呈现明显的缺钾诱导表达模式。研究结果为进一步全面解析HAK/KUP/KT基因在萝卜中的生物学功能以及提高萝卜栽培品质提供了一定理论依据。

根际微生态系统中钾素转化与循环研究进展

钾是植物生长所必需的大量营养元素之一,钾素在植物代谢和植物组织与器官之间营养物质的运输机制中起着关键作用。植物主要通过根部吸收土壤中的钾素并由转运蛋白运输,此外钾素的转化和循环与解钾微生物紧密相关,在植物-土壤-微生物生态系统中起着至关重要的作用。本文综述了根际微生态系统中钾素的转化与循环,包括土壤中钾的存在形式和转化、植物对钾的吸收和利用、土壤微生物解钾菌的研究。深入了解根际微生态领域钾素转化与循环的过程,可为农业生产中钾素调控及植物生态修复提供理论依据。

适度提高血钾浓度可改善心肺复苏大鼠脑组织线粒体功能

目的探讨心肺复苏(CPR)时适度提高血钾浓度能否改善脑组织线粒体功能。方法80只SD大鼠随机分为假手术组(SH组)、生理盐水组(NS组)及氯化钾低(LK组)、中(MK组)和高剂量组(HK组),每组16只。经食道电刺激诱导心室颤动建立心跳骤停(CA)/CPR模型。CA后6 min启动CPR,同时经静脉注射生理盐水或氯化钾。观察并记录自主循环恢复(ROSC)后平均动脉压(MAP)、血钾,以及ROSC后24 h的神经功能缺损评分(NDS)、海马组织HE染色的细胞形态、海马组织ATP含量、Na^(+)/K^(+)-ATP酶活性、呼吸链复合物Ⅰ/Ⅱ/Ⅲ/Ⅳ的活性。结果与NS组相比,MK组、HK组ROSC后1 min、10 min血钾升高(P<0.05)。与NS组相比,MK组复苏后MAP变化差异无统计学意义,ROSC后24 h NDS升高(P<0.05),而HK组ROSC后8 min内的MAP明显下降(P<0.05),ROSC后24 h NDS无改善。与NS组相比,LK组海马组织呼吸链复合物Ⅲ活性升高,ATP生成增加(P<0.05);与NS组相比,MK组ROSC后24 h呼吸链复合物Ⅰ/Ⅱ/Ⅲ活性升高,ATP生成增加、Na^(+)/K^(+)-ATP酶活性升高(P<0.05),ROSC后24 h海马区细胞形态改善;与NS组相比,HK组呼吸链复合物Ⅲ活性升高(P<0.05)。MK组各评估指标改善最明显。结论CPR早期适度升高血钾可改善脑组织线粒体功能,减轻脑缺血再灌注损伤。

Membrane Transporters for Nitrogen,Phosphate and Potassium Uptake in Plants

Nitrogen, phosphorous and potassium are essential nutrients for plant growth and development. However, their contents in soils are limited so that crop production needs to invest a lot for fertilizer supply. To explore the genetic potentialities of crops （or plants） for their nutrient utilization efficiency has been an important research task for many years, in fact, a number of evidences have revealed that plants, during their evolution, have developed many morphological, physiological, biochemical and molecular adaptation mechanisms for acquiring nitrate, phosphate and potassium under stress conditions. Recent discoveries of many transporters and channels for nitrate, phosphate and potassium uptake have opened up opportunities to study the molecular regulatory mechanisms for acquisition of these nutrients. This review aims to briefly discuss the genes and gene families for these transporters and channels, in addition, the functions and regulation of some important transporters and channels are particularly emphasized.

Molecular evolution and functional divergence of HAK potassium transporter gene family in rice(Oryza sativa L.)

The high-affinity K＋ （HAK） transporter gene family is the largest family in plant that functions as potassium transporter and is important for various aspects of plant life. In the present study, we identified 27 members of this family in rice genome. The phylogenetic tree divided the land plant HAK transporter proteins into 6 distinct groups. Although the main characteristic of this family was established before the origin of seed plants, they also showed some differences between the members of non-seed and seed plants. The HAK genes in rice were found to have expanded in lineage-specific manner after the split of monocots and dicots, and both segmental duplication events and tandem duplication events contributed to the expansion of this family. Functional divergence analysis for this family provided statistical evidence for shifted evolutionary rate after gene duplication. Further analysis indicated that both point mutant with positive selection and gene conversion events contributed to the evolution of this family in rice.

Gene Structure and Expression of the High-affinity Nitrate Transport System in Rice Roots

Rice has a preference for uptake of ammonium over nitrate and can use ammonium-N efficiently. Consequently, transporters mediating ammonium uptake have been extensively studied, but nitrate transporters have been largely ignored. Recently, some reports have shown that rice also has high capacity to acquire nitrate from growth medium, so understanding the nitrate transport system in rice roots is very important for improving N use efficiency in rice. The present study Identified four putative NRT2 and two putative NAR2 genes that encode components of the high-affinity nitrate transport system （HATS） in the rice （Oryza sativa L. subsp, japonica cv. Nipponbare） genome. OsNRT2.1 and OsNRT2.2 share an Identical coding region sequence, and their deduced proteins are closely related to those from mono-cotyledonous plants. The two NAR2 proteins are closely related to those from mono-cotyledonous plants as well. However, OsNRT2.3 and OsNRT2.4 are more closely related to Arabidopsis NRT2 proteins. Relative quantitative reverse trsnscription-polymerase chain reaction analysis showed that all of the six genes were rapidly upregulated and then downrsgulated in the roots of N-starved rice plants after they were re-supplied with 0.2 mM nitrate, but the response to nitrate differed among gene members. The results from phylogenetic tree, gene structure and expression analysis implied the divergent roles for the Individual members of the rice NRT2 and NAR2 families. High-affinity nitrate influx rates associated with nitrate induction in rice roots were investigated and were found to be regulated by external pH. Compared with the nitrate influx rates at pH 6.5, alkaline pH （pH 8.0） inhibited nitrate influx, and acidic pH （pH 5.0） enhanced the nitrate influx in 1 h nitrate induced roots, but did not significantly affect that in 4 to 8 h nitrate induced roots.

Regulation of the High-Affinity Nitrate Transport System in Wheat Roots by Exogenous Abscisic Acid and Glutamine

Nitrate is a major nitrogen （N） source for most crops. Nitrate uptake by root cells is a key step of nitrogen metabolism and has been widely studied at the physiological and molecular levels. Understanding how nitrate uptake is regulated will help us engineer crops with improved nitrate uptake efficiency. The present study investigated the regulation of the high-affinity nitrate transport system （HATS） by exogenous abscisic acid （ABA） and glutamine （Gin） in wheat （Triticum aestivum L.） roots. Wheat seedlings grown in nutrient solution containing 2 mmol/L nitrate as the only nitrogen source for 2weeks were deprived of N for 4d and were then transferred to nutrient solution containing 50 μmol/L ABA, and 1 mmol/L Gin in the presence or absence of 2 mmol/L nitrate for 0, 0.5, 1, 2, 4, and 8 h. Treated wheat plants were then divided into two groups. One group of plants was used to investigate the mRNA levels of the HATS components NRT2 and NAR2 genes in roots through semi-quantitative RT-PCR approach, and the other set of plants were used to measure high-affinity nitrate influx rates in a nutrient solution containing 0.2 mmol/L ^15N-labeled nitrate. The results showed that exogenous ABA induced the expression of the TaNRT2.1, TaNRT2.2, TaNRT2.3, TaNAR2.1, and TaNAR2.2 genes in roots when nitrate was not present in the nutrient solution, but did not further enhance the induction of these genes by nitrate. Glutamine, which has been shown to inhibit the expression of NRT2 genes when nitrate is present in the growth media, did not inhibit this induction. When Gin was supplied to a nitrate-free nutrient solution, the expression of these five genes in roots was induced. These results imply that the inhibition by Gin of NRT2 expression occurs only when nitrate is present in the growth media. Although exogenous ABA and Gin induced HATS genes in the roots of wheat, they did not induce nitrate influx.