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 Kt in the presence of toxic concentrations of Nat. This has so far not been well examined in glycophytic crops. Here, we report the characterization of SbHKT1;4, a member of the HKT gene family from Sorghum bicolor. Upon Nat stress, SbHKT1;4 expression was more strongly upregulated in salt‐tolerant sorghum accession, correlating with a better balanced Nat/ Kt 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 Nat stress, and such hypersensitivity could be alleviated with the supply of elevated levels of Kt, implicating that SbHKT1;4 may mediate Kt uptake in the presence of excessive Nat. Further electrophysiological evidence demonstrated that SbHKT1;4 could transport Nat and Kt when expressed in Xenopus laevis oocytes. The relevance of the finding that SbHKT1;4 functions to maintain optimal Nat/Kt balance under Nat stress to the breeding of salt‐tolerant glycophytic crops is discussed.     

The kinetics of IL—4 and IFN—γ gene expression in Mice after Trichosansin immunization

Trichosanthin (TCS) is a potent allergen to mice.According to our previous experiments,it could bring out the IgE response to ovabumin (OVA) if TCS was given one day before OVA immunization,while OVA alone could not induce IgE to it.In this work,the kinetics of interleukin 4(IL-4) and interferon γ(IFN-γ) gene expression in the mesenteric lymph node (MLN) of TCS-immunized mice was investigated using a semi-quantitative RT-PCR method.It indicated that TCS induced significant IL-4 gene expression and the peaks of IL4 gene expression were on day one after TCS immunization in both primary and secondary response.In contrast,the IFN-γ gene expression was suppressed.Furthermor,the IL-4 gene expression in the secondary response was lower than that in the primary response.Thus the presence of IgE memory B cells were studied.Results showed that the amount of mature IgE mRNA arose significantly and rapidly one day after TCS restimulation,while in the MLN of the mice primed 30 days before and without boost,it was almost as the same amount of the unimmunized control.These findings suggest the existence of the IgE memory B cells in the mice after the primary TCS immunization.     

Overexpression of a tobacco small G protein gene NtRop1 causes salt sensitivity and hydrogen peroxide production in transgenic plants

The small GTPases of Rop/Rho family is central regulators of important cellular processes in plants. Tobacco small G protein gene NtRop1 has been isolated; however, its roles in stress responses were unknown. In the present study, the genomic sequence of NtRop1 was cloned, which has seven exons and six introns, similar to the Rop gene structure from Arabidopsis. The NtRop1 gene was constitutively expressed in the different organs whereas the other six Rop genes from tobacco had differential expression patterns. The expression of the NtRop1 gene was moderately induced by methyl viologen, NaCl, and ACC treatments, but slightly inhibited by ABA treatment, with no significant induction by NAA treatment. The transgenic Arabidopsis plants overexpressing the NtRop1 showed increased salt sensitivity as can be seen from the reduced root growth and elevated relative electrolyte leakage. The hydrogen peroxide production was also promoted in the NtRop1-trangenic plants in comparison with wild type plants. These results imply that the NtRop1 may confer salt sensitivity through activation of H2O2 production during plant response to salt stress.     

Transport,signaling, and homeostasis of potassium and sodium in plants

Potassium （K＋） is an essential macronutrient in plants and a lack of K＋ significantly reduces the potential for plant growth and development. By contrast, sodium （Na＋）, while beneficial to some extent, at high concentrations it disturbs and inhibits various physiological processes and plant growth. Due to their chemical similarities, some functions of K＋ can be undertaken by Na＋ but K＋ homeostasis is severely affected by salt stress, on the other hand. Recent advances have highlighted the fascinating regulatory mechanisms of K＋ and Na＋ transport and signaling in plants. This review summarizes three major topics： （i） the transport mechanisms of K＋ and Na＋ from the soil to the shoot and to the cellular - compartments; （ii） the mechanisms through which plants sense and respond to K＋ and Na＋ availability; and （iii） the components involved in maintenance of K＋/Na＋ homeostasis in plants under salt stress.     

Rice Mitogen-activated Protein Kinase Gene Family and Its Role in Biotic and Abiotic Stress Response

The mitogen-activated protein kinase (MAPK) cascade is an important signaling module that transduces extracellu-lar stimuli into intracellular responses in eukaryotic organisms. An increasing body of evidence has shown that theMAPK-mediated cellular signaling is crucial to plant growth and development, as well as biotic and abiotic stressresponses. To date, a total of 17 MAPK genes have been identified from the rice genome. Expression profiling,biochemical characterization and/or functional analysis were carried out with many members of the rice MAPKgene family, especially those associated with biotic and abiotic stress responses. In this review, the phylogeneticrelationship and classification of rice MAPK genes are discussed to facilitate a simple nomenclature and standardannotation of the rice MAPK gene family. Functional data relating to biotic and abiotic stress responses are re-viewed for each MAPK group and show that despite overlapping in functionality, there is a certain level of functionalspecificity among different rice MAP kinases, The future challenges are to functionally characterize each MAPK, toidentify their downstream substrates and upstream kinases, and to genetically manipulate the MAPK signalingpathway in rice crops for the improvement of agronomically important traits.     

Rice Mitogen-activated Protein Kinase Gene Family and Its Role in Biotic and Abiotic Stress Response

The mitogen-activated protein kinase （MAPK） cascade is an important signaling module that transduces extracellular stimuli into intracellular responses in eukaryotic organisms. An increasing body of evidence has shown that the MAPK-mediated cellular signaling is crucial to plant growth and development, as well as biotic and abiotic stress responses. To date, a total of 17 MAPK genes have been Identified from the rice genome. Expression profiling, biochemical characterization and/or functional analysis were carried out with many members of the rice MAPK gene family, especially those associated with biotic and abiotic stress responses. In this review, the phylogenetic relationship and classification of rice MAPK genes are discussed to facilitate a simple nomenclature and standard annotation of the rice MAPK gene family. Functional data relating to biotic and abiotic stress responses are reviewed for each MAPK group and show that despite overlapping in functionality, there is a certain level of functional specificity among different rice MAP kinases. The future challenges are to functionally characterize each MAPK, to identify their downstream substrates and upstream kinases, and to genetically manipulate the MAPK signaling pathway in rice crops for the Improvement of agronomically important traits.     

Characterization of a sodium-regulated glutaminase from cyanobacterium Synechocystis sp. PCC 6803

Glutaminase is widely distributed among microorganisms and mammals with important functions. Lit-tle is known regarding the biochemical properties and functions of the deamidating enzyme glutami-nase in cyanobacteria. In this study a putative glutaminase encoded by gene slr2079 in Synechocystis sp. PCC 6803 was investigated. The slr2079 was expressed as histidine-tagged fusion protein in Es-cherichia coli. The purified protein possessed glutaminase activity, validating the functional assign-ment of the genomic annotation. The apparent Km value of the recombinant protein for glutamine was 26.6 ± 0.9 mmol/L, which was comparable to that for some of other microbial glutaminases. Analysis of the purified protein revealed a two-fold increase in catalytic activity in the presence of 1 mol/L Na . Moreover, the Km value was decreased to 12.2 ± 1.9 mmol/L in the presence of Na . These data demon-strate that the recombinant protein Slr2079 is a glutaminase which is regulated by Na through in-creasing its affinity for substrate glutamine. The slr2079 gene was successfully disrupted in Synecho-cystis by targeted mutagenesis and the △slr2079 mutant strain was analyzed. No differences in cell growth and oxygen evolution rate were observed between △slr2079 and the wild type under standard growth conditions, demonstrating slr2079 is not essential in Synechocystis. Under high salt stress condition, however, △slr2079 cells grew 1.25-fold faster than wild-type cells. Moreover, the photosyn-thetic oxygen evolution rate of △slr2079 cells was higher than that of the wild-type. To further charac-terize this phenotype, a number of salt stress-related genes were analyzed by semi-quantitative RT-PCR. Expression of gdhB and prc was enhanced and expression of desD and guaA was repressed in △slr2079 compared to the wild type. In addition, expression of two key enzymes of ammonium assimi-lation in cyanobacteria, glutamine synthetase (GS) and glutamate synthase (GOGAT) was examined by semi-quantitative RT-PCR. Expression of GOGAT was enhanced in △slr2079 compared to the wild type while GS expression was unchanged. The results indicate that slr2079 functions in the salt stress re-sponse by regulating the expression of salt stress related genes and might not play a major role in glutamine breakdown in Synechocystis.     

Genome-Wide Comparative in silico Analysis of Calcium Transporters of Rice and Sorghum

The mechanism of calcium uptake, translocation and accumulation in Poaceae has not yet been fully understood. To address this issue, we conducted genome-wide comparative in silico analysis of the calcium (Ca2+) transporter gene family of two crop species, rice and sorghum. Gene annotation, identification of upstream cis-acting ele- ments, phylogenetic tree construction and syntenic mapping of the gene family were performed using several bio- informatics tools. A total of 31 Ca2+ transporters, distributed on 9 out of 12 chromosomes, were predicted from rice genome, while 28 Ca2+ transporters predicted from sorghum are distributed on all the chromosomes except chromosome 10 (Chr 10). Interestingly, most of the genes on Chr 1 and Chr 3 show an inverse syntenic relation- ship between rice and sorghum. Multiple sequence alignment and motif analysis of these transporter proteins re- vealed high conservation between the two species. Phylogenetic tree could very well identify the subclasses of channels, ATPases and exchangers among the gene family. The in silico cis-regulatory element analysis suggested diverse functions associated with light, stress and hormone responsiveness as well as endosperm- and meris- tem-specific gene expression. Further experiments are warranted to validate the in silico analysis of the predicted transporter gene family and elucidate the functions of Ca2+ transporters in various biological processes.     

酵母耐盐机制的研究进展

酵母是一种真核模式生物同时也是一种耐盐微生物,其基因表达和信号传导系统的调节机制及离子运输机制与高等真核生物类似。酵母耐盐机制的研究有助于阐明真核生物的耐盐机制。本文综述了酵母在盐胁迫下的信号传导途径和分子应答机制,以及在酵母耐盐机制研究中主要的研究方法。 Abstract:Yeast is a model eukoryotic organism and salt-tolerant microorganism.The regulative mechanism of gene expression and signal transduction and ion transport of yeast is similar to that of higher eukoryotic organism.The research on salt-tolerant mechanism of yeast will be helpful to the illustrate the salt-tolerant mechanism of higher eukoryotic organism.This review summarized the signal transduction pathway and molercular responses of yeast under salt stress and the major research methods in the research on the salt-tolerant mechenism in yeast.     

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.