Potassium Starvation Research Articles

DarA-the central processing unit for the integration of osmotic with potassium and amino acid homeostasis in Bacillus subtilis.

Cyclic di-adenosine monophosphate (c-di-AMP) is a second messenger involved in diverse metabolic processes including osmolyte uptake, cell wall homeostasis, as well as antibiotic and heat resistance. This study investigates the role of the c-di-AMP receptor protein DarA in the osmotic stress response in Bacillus subtilis. Through a series of experiments, we demonstrate that DarA plays a central role in the cellular response to osmotic fluctuations. Our findings show that DarA becomes essential under extreme potassium limitation as well as upon salt stress, highlighting its significance in mediating osmotic stress adaptation. Suppressor screens with darA mutants reveal compensatory mechanisms involving the accumulation of osmoprotectants, particularly potassium and citrulline. Mutations affecting various metabolic pathways, including the citric acid cycle as well as glutamate and arginine biosynthesis, indicate a complex interplay between the osmotic stress response and metabolic regulation. In addition, the growth defects of the darA mutant during potassium starvation and salt stress in a strain lacking the high-affinity potassium uptake systems KimA and KtrAB can be rescued by increased affinity of the remaining potassium channel KtrCD or by increased expression of ktrD, thus resulting in increased potassium uptake. Finally, the darA mutant can respond to salt stress by the increased expression of MleN , which can export sodium ions.IMPORTANCEEnvironmental bacteria are exposed to rapidly changing osmotic conditions making an effective adaptation to these changes crucial for the survival of the cells. In Gram-positive bacteria, the second messenger cyclic di-AMP plays a key role in this adaptation by controlling (i) the influx of physiologically compatible organic osmolytes and (ii) the biosynthesis of such osmolytes. In several bacteria, cyclic di-adenosine monophosphate (c-di-AMP) can bind to a signal transduction protein, called DarA, in Bacillus subtilis. So far, no function for DarA has been discovered in any organism. We have identified osmotically challenging conditions that make DarA essential and have identified suppressor mutations that help the bacteria to adapt to those conditions. Our results indicate that DarA is a central component in the integration of osmotic stress with the synthesis of compatible amino acid osmolytes and with the homeostasis of potassium, the first response to osmotic stress.

The superior growth of Kluyveromyces marxianus at very low potassium concentrations is enabled by the high-affinity potassium transporter Hak1.

The non-conventional yeast Kluyveromyces marxianus has recently emerged as a promising candidate for many food, environment, and biotechnology applications. This yeast is thermotolerant and has robust growth under many adverse conditions. Here, we show that its ability to grow under potassium-limiting conditions is much better than that of Saccharomyces cerevisiae, suggesting a very efficient and high-affinity potassium uptake system(s) in this species. The K. marxianus genome contains two genes for putative potassium transporters: KmHAK1 and KmTRK1. To characterize the products of the two genes, we constructed single and double knock-out mutants in K. marxianus and also expressed both genes in an S. cerevisiae mutant, that lacks potassium importers. Our results in K. marxianus and S. cerevisiae revealed that both genes encode efficient high-affinity potassium transporters, contributing to potassium homeostasis and maintaining plasma-membrane potential and cytosolic pH. In K. marxianus, the presence of HAK1 supports growth at low K+ much better than that of TRK1, probably because the substrate affinity of KmHak1 is about 10-fold higher than that of KmTrk1, and its expression is induced ~80-fold upon potassium starvation. KmHak1 is crucial for salt stress survival in both K. marxianus and S. cerevisiae. In co-expression experiments with ScTrk1 and ScTrk2, its robustness contributes to an increased tolerance of S. cerevisiae cells to sodium and lithium salt stress.

Impact of potassium starvation on the uptake, transportation, photosynthesis, and abiotic stress tolerance

Impact of potassium starvation on the uptake, transportation, photosynthesis, and abiotic stress tolerance

Comprehensive Transcriptome Analysis Uncovers Hub Long Non-coding RNAs Regulating Potassium Use Efficiency in Nicotiana tabacum.

Potassium (K) is the essential element for plant growth. It is one of the critical factors that determine crop yield, quality, and especially leaf development in tobacco. However, the molecular mechanism of potassium use efficiency (KUE), especially non-coding RNA, is still unknown. In this study, tobacco seedlings were employed, and their hydro-cultivation with K treatments of low and sufficient concentrations was engaged. Physiological analysis showed that low potassium treatment could promote malondialdehyde (MDA) accumulation and antioxidant enzyme activities such as peroxidase (POD), ascorbate-peroxidase (APX). After transcriptomic analysis, a total of 10,585 LncRNA transcripts were identified, and 242 of them were significantly differently expressed under potassium starvation. Furthermore, co-expression networks were constructed and generated 78 potential regulation modules in which coding gene and LncRNAs are involved and functional jointly. By further module-trait analysis and module membership (MM) ranking, nine modules, including 616 coding RNAs and 146 LncRNAs, showed a high correlation with K treatments, and 20 hub K-responsive LncRNAs were finally predicted. Following gene ontology (GO) analysis, the results showed potassium starvation inducing the pathway of antioxidative stress which is consistent with the physiology result mentioned above. Simultaneously, a part of detected LncRNAs, such as MSTRG.6626.1, MSTRG.11330.1, and MSTRG.16041.1, were co-relating with a bench of MYB, C3H, and NFYC transcript factors in response to the stress. Overall, this research provided a set of LncRNAs that respond to K concentration from starvation and sufficient supply. Simultaneously, the regulation network and potential co-functioning genes were listed as well. This massive dataset would serve as an outstanding clue for further study in tobacco and other plant species for nutrient physiology and molecular regulation mechanism.

Sustained Control of Pyruvate Carboxylase by the Essential Second Messenger Cyclic di-AMP in Bacillus subtilis.

ABSTRACTIn Bacillus subtilis and other Gram-positive bacteria, cyclic di-AMP is an essential second messenger that signals potassium availability by binding to a variety of proteins. In some bacteria, c-di-AMP also binds to the pyruvate carboxylase to inhibit its activity. We have discovered that in B. subtilis the c-di-AMP target protein DarB, rather than c-di-AMP itself, specifically binds to pyruvate carboxylase both in vivo and in vitro. This interaction stimulates the activity of the enzyme, as demonstrated by in vitro enzyme assays and in vivo metabolite determinations. Both the interaction and the activation of enzyme activity require apo-DarB and are inhibited by c-di-AMP. Under conditions of potassium starvation and corresponding low c-di-AMP levels, the demand for citric acid cycle intermediates is increased. Apo-DarB helps to replenish the cycle by activating both pyruvate carboxylase gene expression and enzymatic activity via triggering the stringent response as a result of its interaction with the (p)ppGpp synthetase Rel and by direct interaction with the enzyme, respectively.

Genome-wide identification of Brassicaceae B-BOX genes and molecular characterization of their transcriptional responses to various nutrient stresses in allotetraploid rapeseed

BackgroundB-box (BBX) genes play important roles in plant growth regulation and responses to abiotic stresses. The plant growth and yield production of allotetraploid rapeseed is usually hindered by diverse nutrient stresses. However, no systematic analysis of Brassicaceae BBXs and the roles of BBXs in the regulation of nutrient stress responses have not been identified and characterized previously.ResultsIn this study, a total of 536 BBXs were identified from nine brassicaceae species, including 32 AtBBXs, 66 BnaBBXs, 41 BoBBXs, 43 BrBBXs, 26 CrBBXs, 81 CsBBXs, 52 BnBBXs, 93 BjBBXs, and 102 BcBBXs. Syntenic analysis showed that great differences in the gene number of Brassicaceae BBXs might be caused by genome duplication. The BBXs were respectively divided into five subclasses according to their phylogenetic relationships and conserved domains, indicating their diversified functions. Promoter cis-element analysis showed that BBXs probably participated in diverse stress responses. Protein-protein interactions between BnaBBXs indicated their functions in flower induction. The expression profiles of BnaBBXs were investigated in rapeseed plants under boron deficiency, boron toxicity, nitrate limitation, phosphate shortage, potassium starvation, ammonium excess, cadmium toxicity, and salt stress conditions using RNA-seq data. The results showed that different BnaBBXs showed differential transcriptional responses to nutrient stresses, and some of them were simultaneously responsive to diverse nutrient stresses.ConclusionsTaken together, the findings investigated in this study provided rich resources for studying Brassicaceae BBX gene family and enriched potential clues in the genetic improvement of crop stress resistance.

Potassium starvation induces autophagy in yeast

Autophagy is a conserved process that recycles cellular contents to promote survival. Although nitrogen limitation is the canonical inducer of autophagy, recent studies have revealed several other nutrients important to this process. In this study, we used a quantitative, high-throughput assay to identify potassium starvation as a new and potent inducer of autophagy in the yeast Saccharomyces cerevisiae We found that potassium-dependent autophagy requires the core pathway kinases Atg1, Atg5, and Vps34, and other components of the phosphatidylinositol 3-kinase complex. Transmission EM revealed abundant autophagosome formation in response to both stimuli. RNA-Seq indicated distinct transcriptional responses: nitrogen affects transport of ions such as copper, whereas potassium targets the organization of other cellular components. Thus, nitrogen and potassium share the ability to influence molecular supply and demand but do so in different ways. Both inputs promote catabolism through bulk autophagy, but result in distinct mechanisms of cellular remodeling and synthesis.

Two Ways To Convert a Low-Affinity Potassium Channel to High Affinity: Control of Bacillus subtilis KtrCD by Glutamate.

Potassium and glutamate are the major cation and anion, respectively, in every living cell. Due to the high concentrations of both ions, the cytoplasm of all cells can be regarded as a potassium glutamate solution. This implies that the concentrations of both ions need to be balanced. While the control of potassium uptake by glutamate is well established for eukaryotic cells, much less is known about the mechanisms that link potassium homeostasis to glutamate availability in bacteria. Here, we have discovered that the availability of glutamate strongly decreases the minimal external potassium concentration required for the highly abundant Bacillus subtilis potassium channel KtrCD to accumulate potassium. In contrast, the inducible KtrAB and KimA potassium uptake systems have high apparent affinities for potassium even in the absence of glutamate. Experiments with mutant strains revealed that the KtrD subunit responds to the presence of glutamate. For full activity, KtrD synergistically requires the presence of the regulatory subunit KtrC and of glutamate. The analysis of suppressor mutants of a strain that has KtrCD as the only potassium uptake system and that experiences severe potassium starvation identified a mutation in the ion selectivity filter of KtrD (Gly282 to Val) that similarly results in a strongly glutamate-independent increase of the apparent affinity for potassium. Thus, this work has identified two conditions that increase the apparent affinity of KtrCD for potassium, i.e., external glutamate and the acquisition of a single point mutation in KtrD.IMPORTANCE In each living cell, potassium is required for maintaining the intracellular pH and for the activity of essential enzymes. Like most other bacteria, Bacillus subtilis possesses multiple low- and high-affinity potassium uptake systems. Their activity is regulated by the second messenger cyclic di-AMP. Moreover, the pools of the most abundant ions potassium and glutamate must be balanced. We report two conditions under which the low-affinity potassium channel KtrCD is able to mediate potassium uptake at low external potassium concentrations: physiologically, the presence of glutamate results in a severely increased potassium uptake. Moreover, this is achieved by a mutation affecting the selectivity filter of the KtrD channel. These results highlight the integration between potassium and glutamate homeostasis in bacteria.

Potassium mediates coordination of leaf photosynthesis and hydraulic conductance by modifications of leaf anatomy.

Typical symptoms of potassium deficiency, characterized as chlorosis or withered necrosis, occur concomitantly with downregulated photosynthesis and impaired leaf water transport. However, the prominent limitations and mechanisms underlying the concerted decreases of leaf photosynthesis and hydraulic conductance are poorly understood. Monocots and dicots were investigated based on responses of photosynthesis and hydraulic conductance and their components and the correlated anatomical determinants to potassium deficiency. We found a conserved pattern in which leaf photosynthesis and hydraulic conductance concurrently decreased under potassium starvation. However, monocots and dicots showed two different hydraulic-redesign strategies: Dicots tended to show a decreased minor vein density, whereas monocots reduced the size of the bundle sheath and its extensions, rather than the minor vein density; both of these strategies may restrain xylem and outside-xylem hydraulic conductance. Additionally, potassium-deprived leaves developed with fewer mesophyll cell-to-cell connections, leading to a reduced area being available for liquid-phase flow. Further quantitative analysis revealed that mesophyll conductance to CO2 and outside-xylem hydraulic resistance were the major contributors to photosynthetic limitation and increased hydraulic resistance, at more than 50% and 60%, respectively. These results emphasize the importance of potassium in the coordinated regulation of leaf photosynthesis and hydraulic conductance through modifications of leaf anatomy.

Grafting alleviates potassium stress and improves growth in tobacco

BackgroundPotassium is a nutrient element necessary for tobacco growth. Tobacco leaves with high potassium content are elastic and tough, rich in oil. And the same time, potassium can also improve the scent and aromatic value of flue-cured tobacco by regulating the synthesis of aromatic hydrocarbons in leaves.. It is an important quality indicator for flue-cured tobacco. However, the potassium concentration in tobacco leaves in most areas of China is generally lower than the global standard for high quality tobacco. Two tobacco genotypes were grafted to each other under different potassium levels to test whether potassium content and plant growth can be improved by grafting in tobacco.ResultsThe growth of tobacco in all treatments was inhibited under potassium starvation, and grafting significantly alleviated this potassium stress in ‘Yunyan 87’. The trends in whole plant K+ uptake and K+ transfer efficiency to the leaves corresponded to the growth results of the different grafts. The nutrient depletion test results showed that the roots of ‘Wufeng No.2’ had higher K+ absorption potential, K+ affinity, and K+ inward flow rate. K+ enrichment circles appeared at the endoderm of the root section in the energy dispersive X-ray figure, indicating that the formation of Casparian strips may be partly responsible for the lower rate of lateral movement of K+ in the roots of ‘Yunyan 87’. Gene expression analysis suggested that energy redistribution at the whole plant level might constitute one strategy for coping with potassium starvation. The feedback regulation effects between scion ‘Wufeng No.2’ and rootstock ‘Yunyan 87’ indicated that the transmission of certain signaling substances had occurred during grafting.Conclusions‘Wufeng No.2’ tobacco rootstock grafting can increase the K+ uptake and transport efficiency of ‘Yunyan 87’ and enhance plant growth under potassium stress. The physiological mechanism of the improved performance of grafted tobacco is related to higher K+ uptake and utilization ability, improved xylem K+ loading capacity, and up-regulated expression of genes related to energy supply systems.

Contributions of radiation interception and radiation-use efficiency to biomass decrease due to potassium starvation depend on potassium deficiency intensities

Yield loss due to insufficient potassium fertilizer supply has been well documented; however, the information about the negative effect of potassium deficiency on crop yield caused by ecophysiological determinants is not enough. A field experiment with three K treatments (severe K deficiency treatment, K1; moderate K deficiency treatment, K2; and sufficient K supply treatment, K3) was conducted to (1) assess the effects of potassium deficiency on green leaf area index (GLAI) reduction; (2) quantify the contributions of single leaf area, leaf senescence, and leaf appearance to GLAI reduction under potassium deficiency; (3) reveal the changes in the contributions of accumulated radiation interception (RIacc) and radiation-use efficiency (RUE) to above-ground biomass (AM) decrease of oilseed rape under different K supplies. GLAI was restrained due to potassium deficiency, with a reduction ranging from 10.6 to 45.4%. The reduced single leaf area and accelerated leaf senescence caused by potassium starvation accounted for 5.9–23.7% and 2.4–29.0% reduction in GLAI, but delayed leaf appearance rate contributed little. The RIacc during the seedling stage in the K1, K2, and K3 treatments was 101.2, 110.7, and 120.0 MJ m− 2, respectively, and the RUE in the K1, K2, and K3 treatments was 1.03, 2.22, and 2.98 g MJ− 1, respectively, which caused a 61.7% and 48.2% reduction of the final harvested AM in the K1 and K2 treatments compared with the K3 treatment. When AM reduction was less than 24.8%, RIacc was the main determining factor; however, it transferred to RUE when biomass decreased more. In conclusion, GLAI decreased due to potassium starvation was mainly caused by the reduced single leaf area and accelerated leaf senescence, and the relative contribution of RIacc and RUE to AM decline was related to the degree of potassium deficiency.

Potassium starvation affects biomass partitioning and sink–source responses in three sweet potato genotypes with contrasting potassium-use efficiency

Rooted single leaves of sweet potato (Ipomoea batatas L.) produce and translocate photosynthates, thus representing an ideal model for characterising the source–sink relationships and responses to various environments. A hydroponics culture study was conducted with rooted single leaves of sweet potato to determine intraspecific variation in growth, biomass partitioning, and associated physiological changes in response to variable potassium (K) supply among genotypes Ji22 (low K-use efficiency), Nan88 (high K-uptake efficiency) and Xu28 (high K-use efficiency). Potassium deficiency suppressed biomass accumulation in blades, petioles and roots in all three genotypes. Root length of diameters <0.25 mm and 0.25–0.5 mm was significantly less for K-deficient than K-sufficient roots of all genotypes, but the difference was proportionally greater in the K-inefficient genotype Ji22 than the other two genotypes. Potassium deficiency also severely inhibited net photosynthesis of blades in Nan88 and Ji22, as well reducing photosynthate translocation, increasing starch, hexose and sucrose concentrations, and decreasing K concentration in blades. The genotypes varied in photosynthesis-related responses to the K deficiency. Xu28 had greater blade K concentration and net photosynthesis as well as stable maximum quantum yield of photosystem II (FV/FM, with FV = FM – F0) under K deficiency, possibly because of a better source–sink balance and more efficient translocation of photosynthates to roots and K to blade compared with genotypes Ji22 and Nan88. Impaired phloem loading during K deficiency was associated with a decline in photosynthetic rate and decreased carbohydrate supply from blades, resulting in restricted root growth.

Lack of 14-3-3 proteins in Saccharomyces cerevisiae results in cell-to-cell heterogeneity in the expression of Pho4-regulated genes SPL2 and PHO84

BackgroundIon homeostasis is an essential property of living organisms. The yeast Saccharomyces cerevisiae is an ideal model organism to investigate ion homeostasis at all levels. In this yeast genes involved in high-affinity phosphate uptake (PHO genes) are strongly induced during both phosphate and potassium starvation, indicating a link between phosphate and potassium homeostasis. However, the signal transduction processes involved are not completely understood. As 14-3-3 proteins are key regulators of signal transduction processes, we investigated the effect of deletion of the 14-3-3 genes BMH1 or BMH2 on gene expression during potassium starvation and focused especially on the expression of genes involved in phosphate uptake.ResultsGenome-wide analysis of the effect of disruption of either BMH1 or BMH2 revealed that the mRNA levels of the PHO genes PHO84 and SPL2 are greatly reduced in the mutant strains compared to the levels in wild type strains. This was especially apparent at standard potassium and phosphate concentrations. Furthermore the promoter of these genes is less active after deletion of BMH1. Microscopic and flow cytometric analysis of cells with GFP-tagged SPL2 showed that disruption of BMH1 resulted in two populations of genetically identical cells, cells expressing the protein and the majority of cells with no detectible expression. Heterogeneity was also observed for the expression of GFP under control of the PHO84 promoter. Upon deletion of PHO80 encoding a regulator of the transcription factor Pho4, the effect of the BMH1 deletion on SPL2 and PHO84 promoter was lost, suggesting that the BMH1 deletion mainly influences processes upstream of the Pho4 transcription factor.ConclusionOur data indicate that that yeast cells can be in either of two states, expressing or not expressing genes required for high-affinity phosphate uptake and that 14-3-3 proteins are involved in the process(es) that establish the activation state of the PHO regulon.

Potassium Starvation Limits Soybean Growth More than the Photosynthetic Processes across CO2 Levels.

Elevated carbon dioxide (eCO2) often enhances plant photosynthesis, growth, and productivity. However, under nutrient-limited conditions the beneficial effects of high CO2 are often diminished. To evaluate the combined effects of potassium (K) deficiency and eCO2 on soybean photosynthesis, growth, biomass partitioning, and yields, plants were grown under controlled environment conditions with an adequate (control, 5.0 mM) and two deficient (0.50 and 0.02 mM) levels of K under ambient CO2 (aCO2; 400 μmol mol−1) and eCO2 (800 μmol mol−1). Results showed that K deficiency limited soybean growth traits more than photosynthetic processes. An ~54% reduction in leaf K concentration under 0.5 mM K vs. the control caused about 45% less leaf area, biomass, and yield without decreasing photosynthetic rate (Pnet). In fact, the steady photochemical quenching, efficiency, and quantum yield of photosystem II, chlorophyll concentration (TChl), and stomatal conductance under 0.5 mM K supported the stable Pnet. Biomass decline was primarily attributed to the reduced plant size and leaf area, and decreased pod numbers and seed yield in K-deficient plants. Under severe K deficiency (0.02 mM K), photosynthetic processes declined concomitantly with growth and productivity. Increased specific leaf weight, biomass partitioning to the leaves, decreased photochemical quenching and TChl, and smaller plant size to reduce the nutrient demands appeared to be the means by which plants adjusted to the severe K starvation. Increased K utilization efficiency indicated the ability of K-deficient plants to better utilize the tissue-available K for biomass accumulation, except under severe K starvation. The enhancement of soybean growth by eCO2 was dependent on the levels of K, leading to a K × CO2 interaction for traits such as leaf area, biomass, and yield. A lack of eCO2-mediated growth and photosynthesis stimulation under severe K deficiency underscored the importance of optimum K fertilization for maximum crop productivity under eCO2. Thus, eCO2 compensated, at least partially, for the reduced soybean growth and seed yield under 0.5 mM K supply, but severe K deficiency completely suppressed the eCO2-enhanced seed yield.

De novo transcriptome analysis of tobacco seedlings and identification of the early response gene network under low-potassium stress.

Tobacco is an economically important crop, and its potassium content can greatly affect the quality of tobacco leaves. However, the molecular mechanism involved in potassium starvation in tobacco has not been elucidated to date. In this study, Illumina (Solexa) sequencing technology was used to analyze the transcriptome of tobacco seedlings under low-potassium stress for 6, 12, and 24 h. After analysis, 107,824 assembled unigenes were categorized into 57 GO functional groups, and 31,379 unigenes (29.08%) were clustered into 25 COG categories. A total of 9945 genes were classified into 233 KEGG pathways, and 15,209 SSRs were found among the 107,824 unigenes. Between the two samples, 1034 genes were differentially expressed. Twelve randomly selected gene expression levels were analyzed by quantitative RT-PCR, and the results were highly consistent with those obtained by Solexa sequencing. Our results provide a comprehensive analysis of the gene-regulatory network of tobacco seedlings under low-potassium stress.

Potassium and Sodium Transport in Yeast.

As the proper maintenance of intracellular potassium and sodium concentrations is vital for cell growth, all living organisms have developed a cohort of strategies to maintain proper monovalent cation homeostasis. In the model yeast Saccharomyces cerevisiae, potassium is accumulated to relatively high concentrations and is required for many aspects of cellular function, whereas high intracellular sodium/potassium ratios are detrimental to cell growth and survival. The fact that S. cerevisiae cells can grow in the presence of a broad range of concentrations of external potassium (10μM-2.5M) and sodium (up to 1.5M) indicates the existence of robust mechanisms that have evolved to maintain intracellular concentrations of these cations within appropriate limits. In this review, current knowledge regarding potassium and sodium transporters and their regulation will be summarized. The cellular responses to high sodium and potassium and potassium starvation will also be discussed, as well as applications of this knowledge to diverse fields, including antifungal treatments, bioethanol production and human disease.

De novo characterization of the alligator weed (Alternanthera philoxeroides) transcriptome illuminates gene expression under potassium deprivation.

As one of the three macronutrients, potassium participates in many physiological processes in plant life cycle. Recently, potassium-dependent transcriptome analysis has been reported in Arabidopsis, rice and soybean. Alligator weed is well known, particularly for its strong ability to accumulate potassium. However, the molecular mechanism that underlies potassium starvation responses has not yet been described. In this study, we used Illumina (Solexa) sequencing technology to analyse the root transcriptome information of alligator weed under low potassium stress. Further analysis suggested that 9253 differentially expressed genes (DEGs) were upregulated, and 2138 DEGs were downregulated after seven days of potassium deficiency. These factors included 121 transcription factors, 108 kinases, 136 transporters and 178 genes that were related to stress. Twelve transcription factors were randomly selected for further analysis. The expression level of each transcription factor was confirmed by quantitative RT-PCR, and the results of this secondary analysis were consistent with the results of Solexa sequencing. Enrichment analysis indicated that 10,993 DEGs were assigned to 54 gene ontology terms and 123 KEGG pathways. Approximately 24% of DEGs belong to the metabolic, ribosome and biosynthesis of secondary metabolite KEGG pathways. Our results provide a comprehensive analysis of the gene regulatory network of alligator weed under low potassium stress, and afford a valuable resource for genetic and genomic research on plant potassium deficiency.

Rice RCN1/OsABCG5 mutation alters accumulation of essential and nonessential minerals and causes a high Na/K ratio, resulting in a salt-sensitive phenotype

Mineral balance and salt stress are major factors affecting plant growth and yield. Here, we characterized the effects of rice (Oryza sativa L.) reduced culm number1 (rcn1), encoding a G subfamily ABC transporter (OsABCG5) involved in accumulation of essential and nonessential minerals, the Na/K ratio, and salt tolerance. Reduced potassium and elevated sodium in field-grown plants were evident in rcn1 compared to original line ‘Shiokari’ and four independent rcn mutants, rcn2, rcn4, rcn5 and rcn6. A high Na/K ratio was evident in the shoots and roots of rcn1 under K starvation and salt stress in hydroponically cultured plants. Downregulation of SKC1/OsHKT1;5 in rcn1 shoots under salt stress demonstrated that normal function of RCN1/OsABCG5 is essential for upregulation of SKC1/OsHKT1;5 under salt stress. The accumulation of various minerals in shoots and roots was also altered in the rcn1 mutant compared to ‘Shiokari’ under control conditions, potassium starvation, and salt and d-sorbitol treatments. The rcn1 mutation resulted in a salt-sensitive phenotype. We concluded that RCN1/OsABCG5 is a salt tolerance factor that acts via Na/K homeostasis, at least partly by regulation of SKC1/OsHKT1;5 in shoots.

Transcriptional response of Saccharomyces cerevisiae to potassium starvation.

BackgroundIon homeostasis is essential for every cell and aberrant cation homeostasis is related to diseases like Alzheimer’s disease and epilepsy. The mechanisms responsible for cation homeostasis are only partly understood. The yeast Saccharomyces cerevisiae is an excellent organism to study fundamental aspects of cation homeostasis. In this study we investigated the transcriptional response of this yeast to potassium starvation by using Serial Analysis of Gene Expression (SAGE)-tag sequencing.ResultsComparison of transcript levels in cells grown for 60 min in media without potassium with those in cells grown under standard potassium concentrations showed that the mRNA levels of 105 genes were significantly (P < 0.01) up-regulated more than 2.0-fold during potassium starvation and the mRNA levels of 172 genes significantly down-regulated. These genes belong to several functional categories. Genes involved in stress response including HSP30, YRO2 and TPO2 and phosphate metabolism including PHO84, PHO5 and SPL2 were highly up-regulated. Analysis of the promoter of PHO84 encoding a high affinity phosphate transporter, revealed that increased PHO84 RNA levels are caused by both increased Pho4-dependent transcription and decreased RNA turnover. In the latter process antisense transcription may be involved. Many genes involved in cell cycle control, and to a lesser extent genes involved in amino acid transport, were strongly down-regulated.ConclusionsOur study showed that yeast cells respond to potassium starvation in a complex way and reveals a direct link between potassium homeostasis and phosphate metabolism.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-1040) contains supplementary material, which is available to authorized users.

Comparative transcriptome profiling of potassium starvation responsiveness in two contrasting watermelon genotypes

Potassium (K) is one of the essential nutrients for crops, and K⁺ deficiency highly restricts crop yield and quality. Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] is an economically important crop that often suffers from K⁺ deficiency. To elucidate the underlying tolerance mechanism of watermelon to K⁺ deficiency and to improve K efficiency of watermelon and other crops in the future, two watermelon genotypes, namely, YS and 8424, that exhibit contrasting K efficiencies were studied to compare their response mechanisms to K⁺ deficiency. YS was more tolerant of K⁺ deficiency and displayed less inhibited root growth than 8424. Roots of YS and 8424 seedlings with or without K⁺ supply were harvested at 6 and 120 h after treatment (HAT), and their transcriptomes were analyzed by Illumina RNA sequencing. Different regulation mechanisms of the root K⁺-uptake genes for short- and long-term stress were observed. Genes involved in jasmonic acid and reactive oxygen species production; Ca²⁺ and receptor-like kinase signaling; lignin biosynthesis; and other stress-related genes were repressed in YS, whereas a large number of such stress-related genes were induced in 8424 at 120 HAT. These results suggested that repressed defense and stress response can save energy for better root growth in YS, which can facilitate K⁺ uptake and increase K efficiency and tolerance to K⁺ deficiency. This study presents the first global root transcriptome in watermelon and provides new insights into the molecular mechanisms underlying tolerance to K⁺ deficiency of K-efficient watermelon genotypes.