Expression and responses to dehydration and salinity stresses of V-PPase gene members in wheat

Physical Mapping of QTLs for Root Traits in a Population of Recombinant Inbred Lines of Hexaploid Wheat

Root architecture is key in determining how effective plants are at intercepting and absorbing nutrients and water. Previously, the wheat (Triticum aestivum) cultivars Spica and Maringa were shown to have contrasting root morphologies. These cultivars were crossed to generate an F_6:1 population of recombinant inbred lines (RILs) which was genotyped using a 90 K single nucleotide polymorphisms (SNP) chip. A total of 227 recombinant inbred lines (RILs) were grown in soil for 21 days in replicated trials under controlled conditions. At harvest, the plants were scored for seven root traits and two shoot traits. An average of 7.5 quantitative trait loci (QTL) were associated with each trait and, for each of these, physical locations of the flanking markers were identified using the Chinese Spring reference genome. We also compiled a list of genes from wheat and other monocotyledons that have previously been associated with root growth and morphology to determine their physical locations on the Chinese Spring reference genome. This allowed us to determine whether the QTL discovered in our study encompassed genes previously associated with root morphology in wheat or other monocotyledons. Furthermore, it allowed us to establish if the QTL were co-located with the QTL identified from previously published studies. The parental lines together with the genetic markers generated here will enable specific root traits to be introgressed into elite wheat lines. Moreover, the comprehensive list of genes associated with root development, and their physical locations, will be a useful resource for researchers investigating the genetics of root morphology in cereals.

Proton-pumping pyrophosphatase homeolog expression is a dynamic trait in bread wheat (Triticum aestivum)

Proton-pumping pyrophosphatases (H+-PPases) have been shown to enhance biomass and yield. However, to date, there has been little work towards identify genes encoding H+-PPases in bread wheat (Triticum aestivum) (TaVPs) and limited knowledge on how the expression of these genes varies across different growth stages and tissue types. In this study, the IWGSC database was used to identify two novel TaVP genes, TaVP4 and TaVP5, and elucidate the complete homeolog sequences of the three known TaVP genes, bringing the total number of bread wheat TaVPs from 9 to 15. Gene expression levels of each TaVP homeolog were assessed using quantitative real-time PCR (qRT-PCR) in four diverse wheat varieties in terms of phenotypic traits related to high vacuolar pyrophosphatase expression. Homeolog expression was analyzed across multiple tissue types and developmental stages. Expression levels of the TaVP homeologs were found to vary significantly between varieties, tissues and plant developmental stages. During early development (Z10 and Z13), expressions of TaVP1 and TaVP2 homeologs were higher in shoot tissue than root tissue, with both shoot and root expression increasing in later developmental stages (Z22). TaVP2-D was expressed in all varieties and tissue types and was the most highly expressed homeolog at all developmental stages. Expression of the TaVP3 homeologs was restricted to developing grain (Z75), while TaVP4 homeolog expression was higher at Z22 than earlier developmental stages. Variation in TaVP4B was detected among varieties at Z22 and Z75, with Buck Atlantico (high biomass) and Scout (elite Australian cultivar) having the highest levels of expression. These findings offer a comprehensive overview of the bread wheat H+-PPase family and identify variation in TaVP homeolog expression that will be of use to improve the growth, yield, and abiotic stress tolerance of bread wheat.

Molecular characterization and transcriptional regulation of two types of H+-pyrophosphatases in the scuticociliate parasite Philasterides dicentrarchi

Proton-translocating inorganic pyrophosphatases (H⁺-PPases) are an ancient family of membrane bound enzymes that couple pyrophosphate (PPi) hydrolysis to H⁺ translocation across membranes. In this study, we conducted a molecular characterization of two isoenzymes (PdVP1 and PdVP2) located in respectively the alveolar sacs and in the membranes of the intracellular vacuoles of a scuticociliate parasite (Philasterides dicentrarchi) of farmed turbot. We analyzed the genetic expression of the isoenzymes after administration of antiparasitic drugs and after infection in the host. PdVP1 and PdVP2 are encoded by two genes of 2485 and 3069 bp, which respectively contain 3 and 11 exons and express proteins of 746 and 810 aa of molecular mass 78.9 and 87.6 kDa. Topological predictions from isoenzyme sequences indicate the formation of thirteen transmembrane regions (TMRs) for PdVP1 and seventeen TMRs for PdVP2. Protein structure modelling indicated that both isoenzymes are homodimeric, with three Mg²⁺ binding sites and an additional K⁺ binding site in PdVP2. The levels of identity and similarity between the isoenzyme sequences are respectively 33.5 and 51.2%. The molecular weights of the native proteins are 158 kDa (PdVP1) and 178 kDa (PdVP2). The isoenzyme sequences are derived from paralogous genes that form a monophyletic grouping with other ciliate species. Genetic expression of the isoenzymes is closely related to the acidification of alveolar sacs (PdVP1) and intracellular vacuoles (PdVP2): antiparasitic drugs inhibit transcription, while infection increases transcription of both isoenzymes. The study findings show that P. dicentrarchi possesses two isoenzymes with H⁺-PPase activity which are located in acidophilic cell compartment membranes and which are activated during infection in the host and are sensitive to antiparasitic drugs. The findings open the way to using molecular modelling to design drugs for the treatment of scuticociliatosis.

Improved Yield and Photosynthate Partitioning in AVP1 Expressing Wheat (Triticum aestivum) Plants

A fundamental factor to improve crop productivity involves the optimization of reduced carbon translocation from source to sink tissues. Here, we present data consistent with the positive effect that the expression of the Arabidopsis thaliana H+-PPase (AVP1) has on reduced carbon partitioning and yield increases in wheat. Immunohistochemical localization of H+-PPases (TaVP) in spring wheat Bobwhite L. revealed the presence of this conserved enzyme in wheat vasculature and sink tissues. Of note, immunogold imaging showed a plasma membrane localization of TaVP in sieve element- companion cell complexes of Bobwhite source leaves. These data together with the distribution patterns of a fluorescent tracer and [U14C]-sucrose are consistent with an apoplasmic phloem-loading model in wheat. Interestingly, 14C-labeling experiments provided evidence for enhanced carbon partitioning between shoots and roots, and between flag leaves and milk stage kernels in AVP1 expressing Bobwhite lines. In keeping, there is a significant yield improvement triggered by the expression of AVP1 in these lines. Green house and field grown transgenic wheat expressing AVP1 also produced higher grain yield and number of seeds per plant, and exhibited an increase in root biomass when compared to null segregants. Another agriculturally desirable phenotype showed by AVP1 Bobwhite plants is a robust establishment of seedlings.

Genome-wide identification and transcript analysis of vacuolar-ATPase genes in citrus reveal their possible involvement in citrate accumulation

The vacuolar H⁺-ATPase (V-ATPase) proton pump plays an important role in the acidification of vacuoles; however, genes encoding V-ATPase in the citrus genome and their roles in citric acid accumulation remain unclear in citrus fruit. In this study, we found at least one gene encoding subunit A, B, C, D, G, c'', d or e; two genes encoding the subunit E, F, H or a; and four genes encoding subunit c in the citrus genome. Spatial expression analysis showed that most genes were predominantly expressed in the mature leaves and/or flowers but were less expressed in root and juice cells. Two sweet orange (Citrus sinensis) cultivars, 'Anliu' (AL) and 'Hong Anliu' (HAL), which differ in terms of fruit acidity, were used in this study. The citric acid content was significantly higher in 'AL' fruits than in 'HAL' fruits over the entire experimental period (82 days-236 days after full blossom, DAFB). Transcript analysis showed that the transcript levels of most subunit genes, including V₁-A, V₁-B, V₁-C, V₁-E1, V₁-G, V₁-H2 and V₀-a2, V₀-c", V₀-c4, and V₀-d, were significantly lower in 'HAL' than in 'AL' fruits during fruit development and ripening. Moreover, ABA injection significantly increased the citric acid content, simultaneously accompanied by the obvious induction of V₁-A, V₁-C, V₁-E1, V₁-F1, V₁-H2, V₀-a1, V₀-a2, V₀-c1, V₀-c2, V₀-c4, and V₀-d transcription levels. In conclusion, the results demonstrated that V₁-A, V₁-C, V₁-E1, V₁-H2, V₀-a2, V₀-c4, and V₀-d may play more roles than other subunit genes in the vacuole acidification of citrus fruits. The lower activity of V-ATPase caused by the transcript reduction of some subunit genes may be one reason for the low citrate accumulation in 'HAL' juice sacs.

High V-PPase activity is beneficial under high salt loads, but detrimental without salinity

The membrane-bound proton-pumping pyrophosphatase (V-PPase), together with the V-type H+ -ATPase, generates the proton motive force that drives vacuolar membrane solute transport. Transgenic plants constitutively overexpressing V-PPases were shown to have improved salinity tolerance, but the relative impact of increasing PPi hydrolysis and proton-pumping functions has yet to be dissected. For a better understanding of the molecular processes underlying V-PPase-dependent salt tolerance, we transiently overexpressed the pyrophosphate-driven proton pump (NbVHP) in Nicotiana benthamiana leaves and studied its functional properties in relation to salt treatment by primarily using patch-clamp, impalement electrodes and pH imaging. NbVHP overexpression led to higher vacuolar proton currents and vacuolar acidification. After 3 d in salt-untreated conditions, V-PPase-overexpressing leaves showed a drop in photosynthetic capacity, plasma membrane depolarization and eventual leaf necrosis. Salt, however, rescued NbVHP-hyperactive cells from cell death. Furthermore, a salt-induced rise in V-PPase but not of V-ATPase pump currents was detected in nontransformed plants. The results indicate that under normal growth conditions, plants need to regulate the V-PPase pump activity to avoid hyperactivity and its negative feedback on cell viability. Nonetheless, V-PPase proton pump function becomes increasingly important under salt stress for generating the pH gradient necessary for vacuolar proton-coupled Na+ sequestration.

Salinity Tolerance of Two Potato Cultivars (Solanum tuberosum) Correlates With Differences in Vacuolar Transport Activity

Potato is an important cultivated crop species and since it is moderately salt sensitive there is a need to develop more salt tolerant cultivars. A high activity of Na+ transport across the tonoplast in exchange for H+ is essential to reduce Na+ toxicity. The proton motive force (PMF) generated by the V-H+-ATPase and the V-H+-PPase energizes the Na+(K+)/H+ antiport. We compared the activity, gene expression, and protein levels of the vacuolar proton pumps and the Na+/H+ antiporters in two potato cultivars (Solanum tuberosum) contrasting in their salt tolerance (cv. Desiree; tolerant and Mozart; sensitive) grown at 0 and 60 mM NaCl. Tonoplast-enriched vesicles were used to study the pump activity and protein levels of the V-H+-ATPase and the V-H+-PPase and the activity of the Na+/H+ antiporter. Although salt stress reduced the V-H+-ATPase and the V-H+-PPase activity in both cultivars, the decline in H+ pump activity was more severe in the salt-sensitive cultivar Mozart. After salt treatment, protein amounts of the vacuolar H+ pumps decreased in Mozart but remained unchanged in the cultivar Desiree. Decreased protein amounts of the V-H+-PPase found in Mozart may explain the reduced V-H+-PPase activity found for Mozart after salt stress. Under non-stress conditions, protein amounts of V-H+-PPase were equal in both cultivars while the V-H+-PPase activity was already twice as high and remained higher after salt treatment in the cultivar Desiree as compared to Mozart. This cultivar-dependent V-H+-PPase activity may explain the higher salt tolerance of Desiree. Moreover, combined with reduced vacuolar H+ pump activity, Mozart showed a lower Na+/H+ exchange activity and the Km for Na+ is at least twofold lower in tonoplast vesicles from Desiree, what suggests that NHXs from Desiree have a higher affinity for Na+ as compared to Mozart. From these results, we conclude that the higher capacity in combination with the higher affinity for Na+ uptake can be an important factor to explain the differences in salt tolerance of these two potato cultivars.

Regulation of H+-pyrophosphatase by 14-3-3 Proteins from Arabidopsis thaliana

Plant vacuolar H⁺-transporting inorganic pyrophosphatase (V-PPase; EC 3.6.1.1) is a crucial enzyme that exists on the tonoplast to maintain pH homeostasis across the vacuolar membrane. This enzyme generates proton gradient between cytosol and vacuolar lumen by hydrolysis of a metabolic byproduct, pyrophosphate (PP _i ). The regulation of V-PPase at protein level has drawn attentions of many workers for decades, but its mechanism is still unclear. In this work, we show that AVP1, the V-PPase from Arabidopsis thaliana, is a target protein for regulatory 14-3-3 proteins at the vacuolar membrane, and all twelve 14-3-3 isoforms were analyzed for their association with AVP1. In the presence of 14-3-3ν, -µ, -ο, and -ι, both enzymatic activities and its associated proton pumping of AVP1 were increased. Among these 14-3-3 proteins, 14-3-3 µ shows the highest stimulation on coupling efficiency. Furthermore, 14-3-3ν, -µ, -ο, and -ι exerted protection of AVP1 against the inhibition of suicidal substrate PP _i at high concentration. Moreover, the thermal profile revealed the presence of 14-3-3ο improves the structural stability of AVP1 against high temperature deterioration. Additionally, the 14-3-3 proteins mitigate the inhibition of Na⁺ to AVP1. Besides, the binding sites/motifs of AVP1 were identified for each 14-3-3 protein. Taken together, a working model was proposed to elucidate the association of 14-3-3 proteins with AVP1 for stimulation of its enzymatic activity.

AVP1: One Protein, Many Roles

Constitutive expression of the Arabidopsis vacuolar proton-pumping pyrophosphatase (H⁺-PPase) gene (AVP1) increases plant growth under various abiotic stress conditions and, importantly, under nonstressed conditions. Many interpretations have been proposed to explain these phenotypes, including greater vacuolar ion sequestration, increased auxin transport, enhanced heterotrophic growth, and increased transport of sucrose from source to sink tissues. In this review, we evaluate all the roles proposed for AVP1, using findings published to date from mutant plants lacking functional AVP1 and transgenic plants expressing AVP1. It is clear that AVP1 is one protein with many roles, and that one or more of these roles act to enhance plant growth. The complexity suggests that a systems biology approach to evaluate biological networks is required to investigate these intertwined roles.

VvVHP1; 2 Is Transcriptionally Activated by VvMYBA1 and Promotes Anthocyanin Accumulation of Grape Berry Skins via Glucose Signal

In this work, four vacuolar H⁺-PPase (VHP) genes were identified in the grape genome. Among them, VvVHP1; 2 was strongly expressed in berry skin and its expression exhibited high correlations to anthocyanin content of berry skin during berry ripening and under ABA and UVB treatments. VvVHP1; 2 was transcriptionally activated directly by VvMYBA1, and VvVHP1; 2 overexpression promoted anthocyanin accumulation in berry skins and Arabidopsis leaves; therefore, VvVHP1; 2 mediated VvMYBA1-regulated berry pigmentation. On the other hand, RNA-Seq analysis of WT and transgenic berry skins revealed that carbohydrate metabolism, flavonoid metabolism and regulation and solute carrier family expression were the most clearly altered biological processes. Further experiments elucidated that VvVHP1; 2 overexpression up-regulated the expression of the genes related to anthocyanin biosynthesis and transport via hexokinase-mediated glucose signal and thereby promoted anthocyanin accumulation in berry skins and Arabidopsis leaves. Additionally, modifications of sugar status caused by enhanced hexokinase activities likely play a key role in VvVHP1; 2-induced sugar signaling.

Cloning and Characterisation of Two H+ Translocating Organic Pyrophos-phatase Genes in Salix and Their Expression Differences in Two Willow Varieties with Different Salt Tolerances

Willows are one of the most important tree species for landscaping, biofuel and raw timber. Screening salt-tolerant willow varieties is an effective approach to balance wood supply and demand. However, more salt-tolerant willow varieties are required and little is known regarding the mechanism of salt tolerance at the gene expression level. In this paper, two willow varieties were studies in terms of their differences in salt-tolerances and mechanism of salt tolerance at the level of VP1 gene expression. The results showed that Salix L0911 (L0911) had higher biomass than Salix matsudana (SM), and salt injuries were less severe in L0911 than in SM. The activities of peroxidase and superoxide dismutase, as well as the contents of soluble protein and proline, were higher in L0911 than in SM, whereas the contents of Na(+) and K(+), as well as the Na(+)/K(+) ratio, were lower in L0911 than in SM. Two VP1 genes (VP1.1 and VP1.2) cloned in L0911 and SM had similar sequences and structures. VP1.1 and VP1.2 belonged to different subgroups. Total expression levels of the VP1.1 gene in both roots and leaves of L0911 were higher than that in SM under normal conditions. Under salt stress, expression of VP1 in SM roots initially increased and then decreased, whereas the expression of VP1 in leaves of L0911 and SM, as well as in roots of L0911, decreased with increasing salt concentrations. This study increased our understanding of the salt-tolerance mechanism of willow and may facilitate the selection of salt-tolerant willow resources.

Pigmentation in sand pear (Pyrus pyrifolia) fruit: biochemical characterization, gene discovery and expression analysis with exocarp pigmentation mutant

Exocarp color of sand pear is an important trait for the fruit production and has caused our concern for a long time. Our previous study explored the different expression genes between the two genotypes contrasting for exocarp color, which indicated the different suberin, cutin, wax and lignin biosynthesis between the russet- and green-exocarp. In this study, we carried out microscopic observation and Fourier transform infrared spectroscopy analysis to detect the differences of tissue structure and biochemical composition between the russet- and green-exocarp of sand pear. The green exocarp was covered with epidermis and cuticle which was replaced by a cork layer on the surface of russet exocarp, and the chemicals of the russet exocarp were characterized by lignin, cellulose and hemicellulose. We explored differential gene expression between the russet exocarp of 'Niitaka' and its green exocarp mutant cv. 'Suisho' using Illumina RNA-sequencing. A total of 559 unigenes showed different expression between the two types of exocarp, and 123 of them were common to the previous study. The quantitative real time-PCR analysis supports the RNA-seq-derived gene with different expression between the two types of exocarp and revealed the preferential expression of these genes in exocarp than in mesocarp and fruit core. Gene ontology enrichment analysis revealed divorced expression of lipid metabolic process genes, transport genes, stress responsive genes and other biological process genes in the two types of exocarp. Expression changes in lignin metabolism-related genes were consistent with the different pigmentation of russet and green exocarp. Increased transcripts of putative genes involved the suberin, cutin and wax biosynthesis in 'Suisho' exocarp could facilitate deposition of the chemicals and take a role in the mutant trait responsible for the green exocarp. In addition, the divorced expression of ATP-binding cassette transporters involved in the trans-membrane transport of lignin, cutin, and suberin precursors suggests that the transport process could also affect the composition of exocarp and take a role in the regulation of exocarp pigmentation. Results from this study provide a base for the analysis of the molecular mechanism underlying sand pear russet/green exocarp mutation, and presents a comprehensive list of candidate genes that could be used to further investigate the trait mutation at the molecular level.

Classification and expression diversification of wheat dehydrin genes

Dehydrins (DHNs) are late embryonic abundant proteins characterized by the dehydrin domains that are involved in plant abiotic stress tolerance. In this study, fifty-four wheat DHN unigenes were identified in the expressed sequence tags database. These genes encode seven types of dehydrins (KS, SK3, YSK2, Y2SK2, Kn, Y2SK3, and YSK3) and separate in 32 homologous clusters. The gene amplification differed among the dehydrin types, and members of the YSK2- and Kn-type DHNs are more numerous in wheat than in other cereals. The relative expression of all of these DHN clusters was analyzed using an in silico method in seven tissue types (i.e. normal growing shoots, roots, and reproductive tissues; developing and germinating seeds; drought- and cold-stressed shoots) as well as semi-quantitative reverse transcription polymerase chain reaction in seedling leaves and roots treated by dehydration, cold, and salt, respectively. The role of the ABA pathway in wheat DHN expression regulation was analyzed. Transcripts of certain types of DHNs accumulated specifically according to tissue type and treatment, which suggests their differentiated roles in wheat abiotic stress tolerance.

Transcriptional regulation of the V-ATPase subunit c and V-PPase isoforms in Cucumis sativus under heavy metal stress

Two electrogenic proton pumps, vacuolar H(+) transporting ATPase (V-ATPase, EC 3.6.3.14) and vacuolar H(+) transporting inorganic pyrophosphatase (V-PPase, EC 3.6.1.1), co-exist in the vacuolar membrane of plant cells. In this work, all CsVHA and CsVHP genes encoding V-ATPase and V-PPase, respectively, were identified in the cucumber genome. Among them, three CsVHA-c genes for V-ATPase subunit c and two CsVHP1 genes for type I V-PPase were analyzed in detail. Individual isogenes were differentially regulated in plant tissues and during plant development as well as under changing environmental conditions. CsVHA-c1 and CsVHA-c2 showed similar tissue-specific expression patterns with the highest levels in stamens and old leaves. CsVHP1;1 was predominantly expressed in roots and female flowers. In contrast, both CsVHA-c3 and CsVHP1;2 remained in a rather constant ratio in all examined cucumber organs. Under heavy metal stress, the transcript amount of CsVHA-c1 and CsVHP1;1 showed a pronounced stress-dependent increase after copper and nickel treatment. CsVHA-c3 was upregulated by nickel only whereas CsVHA-c2 was induced by all metals with the most visible effect of copper. Additionally, CsVHP1;2 showed a tendency to be upregulated by copper and zinc. We propose that CsVHA-c1, CsVHA-c2 and CsVHP1;1 are essential elements of mechanisms involved in adaptation of cucumber plants to copper toxicity.

Drought and salt tolerance enhancement of transgenic Arabidopsis by overexpression of the vacuolar pyrophosphatase 1 (EVP1) gene from Eucalyptus globulus

Vacuolar solute accumulation has been shown to be a mechanism by which plants are capable of increasing drought and salt tolerance. The exposure of plants to NaCl induces H+ transport into the vacuole by specialized pumps. One of them corresponds to the vacuolar H+-pyrophosphatase, which generates a H+ gradient across the vacuolar membrane. In our laboratory we isolated the first cDNA sequence of a vacuolar pyrophosphatase type I (EVP1) from Eucalyptus globulus. Using real-time PCR we confirmed that EVP1 participates in Eucalyptus plants' response to drought and salt stress through an ABA independent pathway. Additionally, the overexpression of EVP1 in transgenic Arabidopsis resulted in an enhancement of drought and salt tolerance. Interestingly we established that the transgenic plants had a higher number of root hairs, which may have a positive effect on the plant's response to drought and salt stress. These results suggest that EVP1 plays an active role in abiotic stress tolerance in E. globulus, and that it may be potentially used to enhance drought and stress tolerance of plants.

Drought tolerance in wheat

Drought is one of the most important phenomena which limit crops' production and yield. Crops demonstrate various morphological, physiological, biochemical, and molecular responses to tackle drought stress. Plants' vegetative and reproductive stages are intensively influenced by drought stress. Drought tolerance is a complicated trait which is controlled by polygenes and their expressions are influenced by various environmental elements. This means that breeding for this trait is so difficult and new molecular methods such as molecular markers, quantitative trait loci (QTL) mapping strategies, and expression patterns of genes should be applied to produce drought tolerant genotypes. In wheat, there are several genes which are responsible for drought stress tolerance and produce different types of enzymes and proteins for instance, late embryogenesis abundant (lea), responsive to abscisic acid (Rab), rubisco, helicase, proline, glutathione-S-transferase (GST), and carbohydrates during drought stress. This review paper has concentrated on the study of water limitation and its effects on morphological, physiological, biochemical, and molecular responses of wheat with the possible losses caused by drought stress.

Plant nitrogen assimilation and use efficiency

Crop productivity relies heavily on nitrogen (N) fertilization. Production and application of N fertilizers consume huge amounts of energy, and excess is detrimental to the environment; therefore, increasing plant N use efficiency (NUE) is essential for the development of sustainable agriculture. Plant NUE is inherently complex, as each step-including N uptake, translocation, assimilation, and remobilization-is governed by multiple interacting genetic and environmental factors. The limiting factors in plant metabolism for maximizing NUE are different at high and low N supplies, indicating great potential for improving the NUE of current cultivars, which were bred in well-fertilized soil. Decreasing environmental losses and increasing the productivity of crop-acquired N requires the coordination of carbohydrate and N metabolism to give high yields. Increasing both the grain and N harvest index to drive N acquisition and utilization are important approaches for breeding future high-NUE cultivars.

Multivariate analyses of salt stress and metabolite sensing in auto- and heterotroph Chenopodium cell suspensions

Global warming increases plant salt stress via evaporation after irrigation, but how plant cells sense salt stress remains unknown. Here, we searched for correlation-based targets of salt stress sensing in Chenopodium rubrum cell suspension cultures. We proposed a linkage between the sensing of salt stress and the sensing of distinct metabolites. Consequently, we analysed various extracellular pH signals in autotroph and heterotroph cell suspensions. Our search included signals after 52 treatments: salt and osmotic stress, ion channel inhibitors (amiloride, quinidine), salt-sensing modulators (proline), amino acids, carboxylic acids and regulators (salicylic acid, 2,4-dichlorphenoxyacetic acid). Multivariate analyses revealed hirarchical clusters of signals and five principal components of extracellular proton flux. The principal component correlated with salt stress was an antagonism of γ-aminobutyric and salicylic acid, confirming involvement of acid-sensing ion channels (ASICs) in salt stress sensing. Proline, short non-substituted mono-carboxylic acids (C2-C6), lactic acid and amiloride characterised the four uncorrelated principal components of proton flux. The proline-associated principal component included an antagonism of 2,4-dichlorphenoxyacetic acid and a set of amino acids (hydrophobic, polar, acidic, basic). The five principal components captured 100% of variance of extracellular proton flux. Thus, a bias-free, functional high-throughput screening was established to extract new clusters of response elements and potential signalling pathways, and to serve as a core for quantitative meta-analysis in plant biology. The eigenvectors reorient research, associating proline with development instead of salt stress, and the proof of existence of multiple components of proton flux can help to resolve controversy about the acid growth theory.

MdVHP1 encodes an apple vacuolar H(+)-PPase and enhances stress tolerance in transgenic apple callus and tomato

Vacuolar H(+)-translocating inorganic pyrophosphatase (VHP, EC 3.6.1.1) is an electrogenic proton pump, which is related to growth as well as abiotic stress tolerance in plants. In this study, a VHP gene MdVHP1 was isolated from apple. The alignment of nucleotide and amino acid sequences showed that it encoded a type I VHP protein. It expressed in vegetative and reproductive organs, and its expression was induced by salt, PEG-mediated osmotic stress, cold and heat in apple in vitro shoot cultures. MdVHP1 expression showed a similar pattern in different apple tissues, but different change dynamics in response to abiotic stresses, compared with MdVHP2 (another MdVHP gene in apple). MdVHP1 overexpression enhanced tolerance to salt, PEG-mimic drought, cold and heat in transgenic apple calluses, which was related to an increased accumulation of proline and decreased MDA content compared with control calluses. In addition, MdVHP1 overexpression confers improved tolerance to salt and drought in transgenic tomato, along with an increased ion accumulation, high RWC and low solute potential compared with wild type. These results indicate that MdVHP1 is an important regulator for plant tolerance to abiotic stresses by modulating internal stores of ions and solutes.

Sodium transport in plants: a critical review

Sodium (Na) toxicity is one of the most formidable challenges for crop production world-wide. Nevertheless, despite decades of intensive research, the pathways of Na(+) entry into the roots of plants under high salinity are still not definitively known. Here, we review critically the current paradigms in this field. In particular, we explore the evidence supporting the role of nonselective cation channels, potassium transporters, and transporters from the HKT family in primary sodium influx into plant roots, and their possible roles elsewhere. We furthermore discuss the evidence for the roles of transporters from the NHX and SOS families in intracellular Na(+) partitioning and removal from the cytosol of root cells. We also review the literature on the physiology of Na(+) fluxes and cytosolic Na(+) concentrations in roots and invite critical interpretation of seminal published data in these areas. The main focus of the review is Na(+) transport in glycophytes, but reference is made to literature on halophytes where it is essential to the analysis.