Potassium Transporter Gene Research Articles

Evolution of polyamine resistance in Staphylococcus aureus through modulation of potassium transport.

Microbes must adapt to diverse biotic and abiotic factors encountered in host environments. Polyamines are an abundant class of aliphatic molecules that play essential roles in fundamental cellular processes across the tree of life. Surprisingly, the bacterial pathogen Staphylococcus aureus is highly sensitive to polyamines encountered during infection, and acquisition of a polyamine resistance locus has been implicated in spread of the prominent USA300 methicillin-resistant S. aureus lineage. At present, alternative pathways of polyamine resistance in staphylococci are largely unknown. Here we applied experimental evolution to identify novel mechanisms and consequences of S. aureus adaption when exposed to increasing concentrations of the polyamine spermine. Evolved populations of S. aureus exhibited striking evidence of parallel adaptation, accumulating independent mutations in the potassium transporter genes ktrA and ktrD. Mutations in either ktrA or ktrD are sufficient to confer polyamine resistance and function in an additive manner. Moreover, we find that ktr mutations provide increased resistance to multiple classes of unrelated cationic antibiotics, suggesting a common mechanism of resistance. Consistent with this hypothesis, ktr mutants exhibit alterations in cell surface charge indicative of reduced affinity and uptake of cationic molecules. Finally, we observe that laboratory-evolved ktr mutations are also present in diverse natural S. aureus isolates, suggesting these mutations may contribute to antimicrobial resistance during human infections. Collectively this study identifies a new role for potassium transport in S. aureus polyamine resistance with consequences for susceptibility to both host-derived and clinically-used antimicrobials.

Genome-Wide Identification, Characterization, and Expression of the HAK/KUP/KT Potassium Transporter Gene Family in Poncirus trifoliata and Functional Analysis of PtKUP10 under Salt Stress

Potassium is an essential mineral nutrient for citrus growth and stress response. In this study, the HAK/KUP/KT gene family was identified from the genome of trifoliate orange (Poncirus trifoliata). The physical and chemical properties, chromosomal location, gene structure, evolutionary relationship, conserved motifs, and tissue expression characteristics were analyzed. The expression characteristics under low potassium and salt stress were analyzed by fluorescence quantitative PCR. The function of PtKUP10 was investigated by heterologous expression in Arabidopsis thaliana. The results showed that at least 18 PtKUPs were distributed in seven chromosomes. Phylogenetic analysis showed that four PtKUPs clustered in clade I, which mediated the high-affinity potassium absorption. Gene expression analysis showed that four PtKUPs were highly expressed in root, seven PtKUPs were up-regulated by low potassium stress, and nine PtKUPs were up-regulated by salt stress. The cis-acting elements on the promoter of PtKUPs were predominantly involved in stress and hormone responses. Overexpression of PtKUP10 in Arabidopsis thaliana could enhance salt tolerance by accumulating more potassium in the shoot and reducing sodium content in the shoots and roots. These results indicated that PtKUPs play important roles in potassium absorption and salt stress response, and PtKUP10 might enhance salt tolerance by maintaining potassium and sodium homeostasis.

Effect of salinity stress on growth, chlorophyll, antioxidant enzymes and nutrient content in Azolla spp.

Azolla is an aquatic fern that has a symbiotic association with nitrogen-fixing cyanobacteria. It is mainly used as a biofertilizer in rice; however, its potential under salt-affected rice cultivated area was compromised. Therefore, the present study was undertaken to understand the effect of salinity stress on morpho-physiological, biochemical characteristics, photosynthetic efficacy, nutrient and High Affinity Potassium Transporter (HKT) genes in Azolla. The results indicated that out of 102, 8 Azolla (A. microphylla, BLCC 5, BLCC 18, BLCC 28, Pa Car WTY, R 18, R 54 and R 59) were found tolerant to 80 mM NaCl. The best species for salt tolerant (80 mM NaCl) was A. microphylla, whereas the least-tolerant was A. rubra. Fresh biomass production, frond length and width in A. microphylla were significantly (p < 0.05) higher in A. microphylla than A. rubra in both 40 and 80 mM NaCl. Moreover, chlorophyll a/b ratio, carotenoids and chlorophyll fluorescence (CHF)-derived FO, Fm, Fv/Fm and root architecture (root length, average root diameter, root volume, projectile and surface area) were higher in A. microphylla than A. rubra under 40 and 80 mM NaCl. Contents of Na+ and Ca2+ increased in both A. microphylla and A. rubra, which can interfere with the uptake of essential macronutrients; however, these were accumulated comparatively less in A. microphylla than A. rubra, whereas a reverse trend was observed in cellular accumulation of K+ content. A. microphylla had higher superoxide dismutase (SOD), ascorbate peroxidase (APX), and proline activities in 40 and 80 mM NaCl than A. rubra. For the first time, twenty six HKT primers were designed as a molecular marker to identify salt-tolerant Azolla. Out of these, three HKT primers (Req 6, Aeq14, and Aeq16) were amplified in A. microphylla under NaCl stress, while their amplifications were not observed in A. rubra (salt susceptible). In A. microphylla, the expression of the Req 6 (HKT) gene were more under NaCl stress. Moreover, further research is needed to discover and validate the biochemical and molecular processes that confer salinity tolerance in Azolla plants.

Exogenous spermidine improved the salinity-alkalinity stress tolerance of grapevine (Vitis vinifera) by regulating antioxidant system, Na+/K+ homeostasis and endogenous polyamine contents

Salinity-alkalinity stress severely limits the growth and yield of grapes. Spermidine (Spd), a type of polyamine, has been found to play a critical role in improving plant tolerance against abiotic stresses. However, the effect of exogenous Spd on the tolerance to salinity and alkalinity of grape seedlings and its mechanism are poorly understood. In the present study, we investigated the function of exogenous Spd in the salinity-alkalinity stress response of grape seedlings (Vitis vinifera L.). The results showed that salinity-alkalinity stress led to yellowing and wilting of grape leaves, and a decrease in the photosynthetic rate, while exogenous Spd significantly alleviated the damage of salinity-alkalinity stress and maintained the photosynthetic capacity. Exogenous Spd can improve the activity of antioxidant enzyme, and thereby scavenge the reactive oxygen species (ROS) induced by salinity-alkalinity stress. Moreover, exogenous Spd reduced Na+ accumulation and improved K+ content in grape leaves under salinity-alkalinity stress by upregulated the expression levels of VvNHXP (Na+/H+ antiporter) and VvHKT2 (potassium transporter) genes. In addition, exogenous Spd treatment promoted the accumulation of endogenous free Spd and spermine (Spm), and decreased the free putrescine (Put) content in leaves of grape seedlings under salinity-alkalinity stress. Taken together, these results suggest that exogenous Spd can effectively alleviate the salinity-alkalinity stress suffered by grape seedlings, which may contribute to the development of the grape industry in saline alkali areas.

Identification of the High-Affinity Potassium Transporter Gene Family (HKT) in Brassica U-Triangle Species and Its Potential Roles in Abiotic Stress in Brassica napus L.

Members of the high-affinity potassium transporter (HKT) protein family regulate the uptake and homeostasis of sodium and potassium ions, but little research describes their roles in response to abiotic stresses in rapeseed (Brassica napus L.). In this study, we identified and characterized a total of 36 HKT genes from the species comprising the triangle of U model (U-triangle species): B. rapa, B. nigra, B. oleracea, B. juncea, B. napus, and B. carinata. We analyzed the phylogenetic relationships, gene structures, motif compositions, and chromosomal distributions of the HKT family members of rapeseed. Based on their phylogenetic relationships and assemblage of functional domains, we classified the HKT members into four subgroups, HKT1;1 to HKT1;4. Analysis of the nonsynonymous substitutions (Ka), synonymous substitutions (Ks), and the Ka/Ks ratios of HKT gene pairs suggested that these genes have experienced strong purifying selective pressure after duplication, with their evolutionary relationships supporting the U-triangle theory. Furthermore, the expression profiles of BnaHKT genes varies among potassium, phytohormone and heavy-metal treatment. Their repression provides resistance to heavy-metal stress, possibly by limiting uptake. Our results systematically reveal the characteristics of HKT family proteins and their encoding genes in six Brassica species and lay a foundation for further exploration of the role of HKT family genes in heavy-metal tolerance.

Waterlogging restricted cotton fiber elongation by reducing osmolyte accumulation and cell wall biosynthesis

Waterlogging severely threatens the formation of cotton fiber quality, especially the length. However, the underlying mechanism is still incompletely understood. Here, the experiment (control: soil relative water content at (75 ± 5)%; treatment: waterlogging for 6 days) was conducted during the flowering and boll forming stage using two upland cotton cultivars (Dexiamian 1 and Yuzaomian 9110) to investigate the effects of waterlogging on fiber development from both transcriptomic and physiological levels. The transcriptome analysis of 10 days post anthesis cotton fiber showed that waterlogging significantly regulated the expression of genes associated with fiber elongation events including osmotic solutes accumulation, fiber cell wall biosynthesis, and cell wall remodeling and loosening. Waterlogging decreased the sucrose input into cotton fiber, resulting in reduced sucrose and hexose contents. Under waterlogging, the accumulation of malate and K+ in both cultivars was reduced by decreasing phosphoenolpyruvate carboxylase (PEPC) activity and potassium transporter genes (GhPOT) expression, respectively. Thus, the total concentration of osmolytes was reduced, which dampened cotton fiber elongation. Due to reduced sucrose synthase activity and uridine diphosphate glucose content, the cellulose biosynthesis was limited, leading to decreased fiber cell wall accumulation, which was adverse to fiber elongation. Besides, genes responsible for cell wall remodeling and loosening, including xyloglucan endotransglucosylase/hydrolase genes (GhXTH), α-expansin genes (GhEXPA), and pectin methylesterase genes (GhPME) were also responsive to waterlogging, but in different ways between cultivars. Overall, the shortened cotton fiber could be attributed to reduced osmolytes accumulation and cell wall biosynthesis, whilst the effects of waterlogging on cotton fiber cell wall loosening require further exploration.

Structural features and expression regulation analysis of potassium transporter gene GmHAK5 in soybean (Glycine max L.)

Structural features and expression regulation analysis of potassium transporter gene GmHAK5 in soybean (Glycine max L.)

High-affinity potassium transporter from a mangrove tree Avicennia officinalis increases salinity tolerance of Arabidopsis thaliana

Salinity reduces the growth and productivity of crop plants worldwide. Mangroves have evolved efficient ion homeostasis mechanisms to survive under their natural saline growth habitat. Information obtained from them may be utilized for increasing the salt tolerance of crop plants. We identified and characterized a high-affinity potassium transporter gene (AoHKT1) from Avicennia officinalis. The expression of AoHKT1 was induced by NaCl mainly in the leaves. Functional study by heterologous expression of AoHKT1 in Arabidopsis T-DNA insertional mutants athkt1–1 and athkt1–4 revealed that it could enhance the salt tolerance of the mutant plants. This was accompanied by an increase in K+ accumulation in the leaves. AoHKT1 was localized to the plasma membrane in Arabidopsis, and when expressed in yeast, it could complement the functions of both Na+ and K+ transporters. An attempt was made to identify the upstream regulator of AtHKT1, a close homolog of AoHKT1. Using chromatin immunoprecipitation, luciferase assay and yeast one-hybrid assays, WRKY9 was identified as the main transcription factor in the process. Furthermore, this was corroborated by the observation that AtHKT1 levels were significantly reduced in the atwrky9 seedlings. These findings revealed a part of the molecular regulatory mechanism of HKT1 induction in response to salt treatment in Arabidopsis. Our study suggests that AoHKT1 is a potential candidate for generating crop plants with increased salt tolerance.

FveARF2 negatively regulates fruit ripening and quality in strawberry.

Auxin response factors (ARFs) are transcription factors that play important roles in plants. ARF2 is a member of the ARF family and participates in many plant growth and developmental processes. However, the role of ARF2 in strawberry fruit quality remains unclear. In this study, FveARF2 was isolated from the woodland strawberry 'Ruegen' using reverse transcription-polymerase chain reaction (RT-PCR), which showed that FveARF2 expression levels were higher in the stem than in other organs of the 'Ruegen' strawberry. Moreover, FaARF2 was higher in the white fruit stage of cultivated strawberry fruit than in other stage. Subcellular localization analysis showed that FveARF2 is located in the nucleus, while transcriptional activation assays showed that FveARF2 inhibited transcription in yeast. Silencing FveARF2 in cultivated strawberry fruit revealed earlier coloration and higher soluble solid, sugar, and anthocyanin content in the transgenic fruit than in the control fruit, overexpression of FveARF2 in strawberry fruit delayed ripening and lower soluble solid, sugar, and anthocyanin content compared to the control fruit. Gene expression analysis indicated that the transcription levels of the fruit ripening genes FaSUT1, FaOMT, and FaCHS increased in FveARF2-RNAi fruit and decreased in FveARF2-OE fruit, when compared with the control. Furthermore, yeast one-hybrid (Y1H) and GUS activity experiments showed that FveARF2 can directly bind to the AuxRE (TGTCTC) element in the FaSUT1, FaOMT, and FaCHS promoters in vitro and in vivo. Potassium ion supplementation improved the quality of strawberry fruit, while silencing FveARF2 increased potassium ion content in transgenic fruit. The Y1H and GUS activity experiments also confirmed that FveARF2 could directly bind to the promoter of FveKT12, a potassium transporter gene, and inhibited its expression. Taken together, we found that FveARF2 can negatively regulate strawberry fruit ripening and quality, which provides new insight for further study of the molecular mechanism of strawberry fruit ripening.

Transcriptome-Wide Analysis Revealed the Potential of the High-Affinity Potassium Transporter (HKT) Gene Family in Rice Salinity Tolerance via Ion Homeostasis.

The high-affinity potassium transporter (HKT) genes are key ions transporters, regulating the plant response to salt stress via sodium (Na+) and potassium (K+) homeostasis. The main goal of this research was to find and understand the HKT genes in rice and their potential biological activities in response to brassinosteroids (BRs), jasmonic acid (JA), seawater, and NaCl stress. The in silico analyses of seven OsHKT genes involved their evolutionary tree, gene structures, conserved motifs, and chemical properties, highlighting the key aspects of OsHKT genes. The Gene Ontology (GO) analysis of HKT genes revealed their roles in growth and stress responses. Promoter analysis showed that the majority of the HKT genes participate in abiotic stress responses. Tissue-specific expression analysis showed higher transcriptional activity of OsHKT genes in roots and leaves. Under NaCl, BR, and JA application, OsHKT1 was expressed differentially in roots and shoots. Similarly, the induced expression pattern of OsHKT1 was recorded in the seawater resistant (SWR) cultivar. Additionally, the Na+ to K+ ratio under different concentrations of NaCl stress has been evaluated. Our data highlighted the important role of the OsHKT gene family in regulating the JA and BR mediated rice salinity tolerance and could be useful for rice future breeding programs.

Sulfur-Oxidizing Bacteria From Coal Mine Enhance Sulfur Nutrition in Pigeonpea (Cajanus cajan L.)

The present investigation was carried out to isolate, identify, and characterize sulfur-oxidizing bacteria (SOB) from coal mines and to evaluate the efficient strains for their ability to influence plant growth and S uptake in pigeonpea. Thirteen bacterial isolates belonging to Stenotrophomonas maltophilia (2), Stenotrophomonas pavanii (2), Rhizobium pusense (5), Bacillus velezensis (2), and Paenibacillus massiliensis (2) were obtained. Among these, seven strains that could reduce the pH of thiosulfate broth were further characterized for sulfur oxidation, plant growth-promoting (PGP) attributes, and in planta studies. Among the seven strains characterized, maximum sulfate ion was recorded for S. maltophilia DRC-18-7A (311.43 mg L−1) closely followed by S. pavanii DRC-18-7B (273.44 mg L−1) and S. maltophilia DRC-18-10 (265.75 mg L−1) after 21 days of inoculation. Among the PGP attributes quantified, maximum P solubilization was recorded in case of S. maltophilia DRC-18-7A (24.39 μg ml−1), while highest siderophore production and IAA production were recorded in S. maltophilia DRC-18-10 (14.25%) and R. pusense DRC-18-25 (15.21 μg ml−1), respectively. S. maltophilia DRC-18-7A closely followed by S. pavanii DRC-18-7B outperformed others in enhancing seed germination (%) and vigour indices. Results clearly indicated that microbial inoculants colonized the plant roots and developed biofilm on the root surface. It was further observed that plants treated with microbial inoculants induce an early formation of secondary and tertiary roots in the pigeonpea compared to the untreated control which was further confirmed by assessing the root architecture using the root scanner. Inoculation of these two strains to pigeonpea significantly enhanced plant growth parameters, the activity of reactive oxygen scavenging (ROS) enzymes, and accumulation of flavonoids, carotenoids, and proline both under sterilized and non-sterilized growth medium (sand and soil in 1:3 ratio). The application of microbial inoculants significantly increased the uptake of nitrogen, phosphorus, potassium, and sulfur in plant shoots. Further, transcript level of phosphate, potassium, and sulfur transporter genes significantly increases upon microbial inoculation leading to increased uptake and translocation of P, K, and S in the pigeonpea. The results indicate that S. maltophilia DRC-18-7A and S. pavanii DRC-18-7B could be recommended as inoculants for pigeonpea to improve its growth and sulfur nutrition.

A Novel High-Affinity Potassium Transporter IbHKT-like Gene Enhances Low–Potassium Tolerance in Transgenic Roots of Sweet Potato (Ipomoea batatas (L.) Lam.)

The high-affinity potassium transporters (HKT) mediate K+-Na+ homeostasis in plants. However, the function of enhancing low-potassium tolerance in sweet potato [Ipomoea batatas (L.) Lam.] remains unrevealed. In this study, a novel HKT transporter homolog IbHKT-like gene was cloned from sweet potato, which was significantly induced by potassium deficiency stress. IbHKT-like overexpressing transgenic roots were obtained from a sweet potato cultivar Xuzishu8 using an Agrobacterium rhizogenes-mediated root transgenic system in vivo. Compared with the CK, whose root cells did not overexpress the IbHKT-like gene, overexpression of the IbHKT-like gene protected cell ultrastructure from damage, and transgenic root meristem cells had intact mitochondria, endoplasmic reticulum, and Golgi dictyosomes. The steady-state K+ influx increased by 2.2 times in transgenic root meristem cells. Overexpression of the IbHKT-like gene also improved potassium content in the whole plant, which increased by 63.8% compared with the CK plants. These results could imply that the IbHKT-like gene, as a high-affinity potassium transporter gene, may play an important role in potassium deficiency stress responses.

Comparative genetic, biochemical and physiological analysis of sodium and chlorine in wheat.

Plant with a great diversity shows several responses towards the biotic and abiotic stresses. Among these abiotic stresses, salinity is the main damaging factor as it reduces the yield of wheat plant with moderate salt tolerance. For its survival, plant undergoes through some genetic, biochemical and physiological changes to tackle the stress. This review mainly describes the conditions where various ions present in the soil, especially sodium and chlorine, enter into the plant and the genes or proteins involved with survival mechanism against the damage in plants. Salt stress causes alteration in enzymatic activity and Photosynthesis, oxidative stress, damage of cellular structure and components and ionic imbalance. Ion toxicity stress occur due to accumulation of excessive sodium ion and chloride ion. Transcriptional factors TaPIMP, TaSRG and TaMYBsdu 1 play key role in gene expression mechanism to overcome the stress. High affinity potassium transporter gene family is responsible for salt tolerance in wheat plant. HKT1;4 and HKT1;5 genes are responsible for Na exclusion in Triticum monococcum. Forty QTLs were found with the marker assisted selection in bread wheat for salinity tolerance and some morphological traits, 5 QTLs were related to sodium ion exclusion. In bread wheat, salt stress tolerance mechanism is mainly an exclusion of Na+ ions but also include K+ ion concentration. The salinity tolerant germplasm MW#293 provides an opportunity for the development of future salinity tolerant bread wheat.

Ethylene-induced potassium transporter AcKUP2 gene is involved in kiwifruit postharvest ripening

BackgroundPotassium (K) is important in the regulation of plant growth and development. It is the most abundant mineral element in kiwifruit, and its content increases during fruit ripening. However, how K+ transporter works in kiwifruit postharvest maturation is not yet clear.ResultsHere, 12 K+ transporter KT/HAK/KUP genes, AcKUP1 ~ AcKUP12, were isolated from kiwifruit, and their phylogeny, genomic structure, chromosomal location, protein properties, conserved motifs and cis-acting elements were analysed. Transcription analysis revealed that AcKUP2 expression increased rapidly and was maintained at a high level during postharvest maturation, consistent with the trend of K content; AcKUP2 expression was induced by ethylene, suggesting that AcKUP2 might play a role in ripening. Fluorescence microscopy showed that AcKUP2 is localised in the plasma membrane. Cis-elements, including DER or ethylene response element (ERE) responsive to ethylene, were found in the AcKUP2 promoter sequence, and ethylene significantly enhanced the AcKUP2 promoter activity. Furthermore, we verified that AcERF15, an ethylene response factor, directly binds to the AcKUP2 promoter to promote its expression. Thus, AcKUP2 may be an important potassium transporter gene which involved in ethylene-regulated kiwifruit postharvest ripening.ConclusionsTherefore, our study establishes the first genome-wide analysis of the kiwifruit KT/HAK/KUP gene family and provides valuable information for understanding the function of the KT/HAK/KUP genes in kiwifruit postharvest ripening.

Genome-wide analysis of HAK/KUP/KT potassium transporter genes in banana (Musa acuminata L.) and their tissue-specific expression profiles under potassium stress

Potassium is one of the most essential inorganic cations for plant growth and development. The high affinity K+ (HAK)/K+ uptake (KUP)/K+ transporter (KT) family plays essential roles in the regulation of cellular K+ levels and the maintenance of osmotic balance. However, the roles of these genes in the responses of bananas to low-potassium stress are unclear. In this study, 24 HAK/KUP/KT (MaHAK) genes were identified from banana. These genes were further classified into four groups based on phylogenetic analysis, gene structure and conserved domain analysis. Segmental duplication events played an important role in the expansion of the MaHAK gene family. Transcriptome analysis revealed the expression patterns of MaHAKs in various tissues under different K+ conditions. MaHAK14b was upregulated under both short- and long-term K+-deficient conditions, suggesting that it plays crucial roles in K+ uptake at low K+ concentrations. Furthermore, MaHAK14b mediated K+ uptake when it was heterologously expressed in the yeast mutant R5421 on low K+ medium. Collectively, these findings provide a foundation for further functional analysis of MaHAK genes, which may be used to improve potassium stress resistance in bananas.

Elucidating morpho‐anatomical, physio‐biochemical and molecular mechanism imparting salinity tolerance in oats (Avena sativa)

AbstractSoil salinization drastically affects crop growth, development and yield. In order to tackle salinity, knowledge about stress tolerance mechanism is important to expedite the development of salt‐tolerant cultivars. In this study, 20 oat genotypes consisting of 11 cultivated and nine wild Avena species were evaluated at different levels of salinity with 1:1 NaCl and Na2SO4 salts mixtures under hydroponics and pot experimental set‐up. Drastic reduction was observed in chlorophyll, relative water and K+/Na+ contents, along with yield traits in sensitive genotypes (HFO‐103, Kent and JHO‐2000‐4) when compared with tolerant (HJ‐8, JHO‐99‐2, HFO‐873 and HFO‐878) under elevated salinity. Root anatomical section studies were also critical to screen salinity tolerance among the oat genotypes. Furthermore, the effect of salinity at the transcriptomic level resulted in upregulation of sodium/hydrogen exchanger and potassium transporter genes along with WRKY17 transcription factor, regulating the signalling and osmotic roles in tolerant genotypes (HJ‐8 and HFO‐873). The identified salt‐tolerant oat genotypes reflected wide genetic diversity using SSR markers which can serve as a crucial donor for salt tolerance in oat breeding programmes.

Identification and characterization of HAK/KUP/KT potassium transporter gene family in barley and their expression under abiotic stress

BackgroundHAK/KUP/KT (High-affinity K+ transporters/K+ uptake permeases/K+ transporters) is the largest potassium transporter family in plants, and plays pivotal roles in K+ uptake and transport, as well as biotic and abiotic stress responses. However, our understanding of the gene family in barley (Hordeum vulgare L.) is quite limited.ResultsIn the present study, we identified 27 barley HAK/KUP/KT genes (hereafter called HvHAKs) through a genome-wide analysis. These HvHAKs were unevenly distributed on seven chromosomes, and could be phylogenetically classified into four clusters. All HvHAK protein sequences possessed the conserved motifs and domains. However, the substantial difference existed among HAK members in cis-acting elements and tissue expression patterns. Wheat had the most orthologous genes to barley HAKs, followed by Brachypodium distachyon, rice and maize. In addition, six barley HAK genes were selected to investigate their expression profiling in response to three abiotic stresses by qRT-PCR, and their expression levels were all up-regulated under salt, hyperosmotic and potassium deficiency treatments.ConclusionTwenty seven HAK genes (HvHAKs) were identified in barley, and they differ in tissue expression patterns and responses to salt stress, drought stress and potassium deficiency.

Bioinformatic analysis of promoter, motifs and CpG islands of genes encoding potassium transporters in crop plants

ABSTRACT Potassium transporter genes are essential for plant salt stress tolerance. Identification of gene regulatory elements is vital for the recognition of gene expression patterns. Thus, understanding gene regulatory systems of potassium transporter genes is useful to improve the salt tolerance of crop plants. The present study was aimed at in silico analysis of promoter and regulatory elements of potassium transporter genes in coffee, peanut, soybean, maize, sorghum and potato crops. A total of 19 potassium transporter genes were identified, and the transcription start site (TSS), conserved motif, CpG islands were analysed using various computational tools. The highest promoter prediction score (1) was obtained in one gene sequence (LOC113728271) for Coffea arabica transcription start site, whereas the lowest score (0.8) was recorded in one gene sequence (LOC8065633) for Sorghum bicolor transcription start site. The analysis also showed that 66% of the genes contained more than one transcription start site whereas 63.16% had only one transcription start site. Five motifs were identified. Motif 1 was found as the common promoter motif residing on 78.95% of potassium transporter promoter sequences with an E-value of 3.4e − 002.C2H2 zinc finger transcription factors are predicted to bind to these conserved motifs with high statistical probability (2.28e − 03). Very few CpG islands were observed both in the promoter and body region of the gene sequences using two algorithms. The present study could contribute for better understanding of gene expression and the improvement of crops’ tolerance to environmental stresses through molecular assisted breeding or genetic engineering techniques.

Temporal salt stress-induced transcriptome alterations and regulatory mechanisms revealed by PacBio long-reads RNA sequencing in Gossypium hirsutum

BackgroundCotton (Gossypium hirsutum) is considered a fairly salt tolerant crop however, salinity can still cause significant economic losses by affecting the yield and deteriorating the fiber quality. We studied a salt-tolerant upland cotton cultivar under temporal salt stress to unfold the salt tolerance molecular mechanisms. Biochemical response to salt stress (400 mM) was measured at 0 h, 3 h, 12 h, 24 h and 48 h post stress intervals and single-molecule long-read sequencing technology from Pacific Biosciences (PacBio) combined with the unique molecular identifiers approach was used to identify differentially expressed genes (DEG).ResultsAntioxidant enzymes including, catalase (CAT), peroxidase (POD), superoxide dismutase (SOD) were found significantly induced under temporal salt stress, suggesting that reactive oxygen species scavenging antioxidant machinery is an essential component of salt tolerance mechanism in cotton. We identified a wealth of novel transcripts based on the PacBio long reads sequencing approach. Prolonged salt stress duration induces high number of DEGs. Significant numbers of DEGs were found under key terms related to stress pathways such as “response to oxidative stress”, “response to salt stress”, “response to water deprivation”, “cation transport”, “metal ion transport”, “superoxide dismutase”, and “reductase”. Key DEGs related to hormone (abscisic acid, ethylene and jasmonic acid) biosynthesis, ion homeostasis (CBL-interacting serine/threonine-protein kinase genes, calcium-binding proteins, potassium transporter genes, potassium channel genes, sodium/hydrogen exchanger or antiporter genes), antioxidant activity (POD, SOD, CAT, glutathione reductase), transcription factors (myeloblastosis, WRKY, Apetala 2) and cell wall modification were found highly active in response to salt stress in cotton. Expression fold change of these DEGs showed both positive and negative responses, highlighting the complex nature of salt stress tolerance mechanisms in cotton.ConclusionCollectively, this study provides a good insight into the regulatory mechanism under salt stress in cotton and lays the foundation for further improvement of salt stress tolerance.

The bacterial potassium transporter gene MbtrkH improves K+ uptake in yeast and tobacco.

K+ is an essential nutrient for plant growth and is responsible for many important physiological processes. K+ deficiency leads to crop yield losses, and overexpression of K+ transporter genes has been proven to be an effective way to resolve this problem. However, current research on the overexpression of K+ transporter genes is limited to plant sources. TrkH is a bacterial K+ transporter whose function generally depends on the regulation of TrkA. To date, whether TrkH can improve K+ uptake in eukaryotic organisms is still unknown. In this study, a novel MbtrkH gene was cloned from marine microbial metagenomic DNA. Functional complementation and K+-depletion analyses revealed that MbTrkH functions in K+ uptake in the K+-deficient yeast strain CY162. Moreover, K+-depletion assays revealed that MbtrkH overexpression improves plant K+ uptake. K+ hydroponic culture experiments showed that, compared with WT tobacco lines, MbtrkH transgenic tobacco lines had significantly greater fresh weights, dry weights and K+ contents. These results indicate that MbTrkH promotes K+ uptake independently of TrkA in eukaryotes and provide a new strategy for improving K+-use efficiency in plants.