The effect of potassium nutrition on pest and disease resistance in plants

Ionomic Approaches for Discovery of Novel Stress-Resilient Genes in Plants

Plants, being sessile, face an array of biotic and abiotic stresses in their lifespan that endanger their survival. Hence, optimized uptake of mineral nutrients creates potential new routes for enhancing plant health and stress resilience. Recently, minerals (both essential and non-essential) have been identified as key players in plant stress biology, owing to their multifaceted functions. However, a realistic understanding of the relationship between different ions and stresses is lacking. In this context, ionomics will provide new platforms for not only understanding the function of the plant ionome during stresses but also identifying the genes and regulatory pathways related to mineral accumulation, transportation, and involvement in different molecular mechanisms under normal or stress conditions. This article provides a general overview of ionomics and the integration of high-throughput ionomic approaches with other "omics" tools. Integrated omics analysis is highly suitable for identification of the genes for various traits that confer biotic and abiotic stress tolerance. Moreover, ionomics advances being used to identify loci using qualitative trait loci and genome-wide association analysis of element uptake and transport within plant tissues, as well as genetic variation within species, are discussed. Furthermore, recent developments in ionomics for the discovery of stress-tolerant genes in plants have also been addressed; these can be used to produce more robust crops with a high nutritional value for sustainable agriculture.

Potassium physiology from Archean to Holocene: A higher-plant perspective

In this paper, we discuss biological potassium acquisition and utilization processes over an evolutionary timescale, with emphasis on modern vascular plants. The quintessential osmotic and electrical functions of the K⁺ ion are shown to be intimately tied to K⁺-transport systems and membrane energization. Several prominent themes in plant K⁺-transport physiology are explored in greater detail, including: (1) channel mediated K⁺ acquisition by roots at low external [K⁺]; (2) K⁺ loading of root xylem elements by active transport; (3) variations on the theme of K⁺ efflux from root cells to the extracellular environment; (4) the veracity and utility of the "affinity" concept in relation to transport systems. We close with a discussion of the importance of plant-potassium relations to our human world, and current trends in potassium nutrition from farm to table.

Elucidating the Response of Crop Plants towards Individual, Combined and Sequentially Occurring Abiotic Stresses

In nature, plants are exposed to an ever-changing environment with increasing frequencies of multiple abiotic stresses. These abiotic stresses act either in combination or sequentially, thereby driving vegetation dynamics and limiting plant growth and productivity worldwide. Plants' responses against these combined and sequential stresses clearly differ from that triggered by an individual stress. Until now, experimental studies were mainly focused on plant responses to individual stress, but have overlooked the complex stress response generated in plants against combined or sequential abiotic stresses, as well as their interaction with each other. However, recent studies have demonstrated that the combined and sequential abiotic stresses overlap with respect to the central nodes of their interacting signaling pathways, and their impact cannot be modelled by swimming in an individual extreme event. Taken together, deciphering the regulatory networks operative between various abiotic stresses in agronomically important crops will contribute towards designing strategies for the development of plants with tolerance to multiple stress combinations. This review provides a brief overview of the recent developments in the interactive effects of combined and sequentially occurring stresses on crop plants. We believe that this study may improve our understanding of the molecular and physiological mechanisms in untangling the combined stress tolerance in plants, and may also provide a promising venue for agronomists, physiologists, as well as molecular biologists.

Elucidating the Response of Crop Plants towards Individual, Combined and Sequentially Occurring Abiotic Stresses

In nature, plants are exposed to an ever-changing environment with increasing frequencies of multiple abiotic stresses. These abiotic stresses act either in combination or sequentially, thereby driving vegetation dynamics and limiting plant growth and productivity worldwide. Plants' responses against these combined and sequential stresses clearly differ from that triggered by an individual stress. Until now, experimental studies were mainly focused on plant responses to individual stress, but have overlooked the complex stress response generated in plants against combined or sequential abiotic stresses, as well as their interaction with each other. However, recent studies have demonstrated that the combined and sequential abiotic stresses overlap with respect to the central nodes of their interacting signaling pathways, and their impact cannot be modelled by swimming in an individual extreme event. Taken together, deciphering the regulatory networks operative between various abiotic stresses in agronomically important crops will contribute towards designing strategies for the development of plants with tolerance to multiple stress combinations. This review provides a brief overview of the recent developments in the interactive effects of combined and sequentially occurring stresses on crop plants. We believe that this study may improve our understanding of the molecular and physiological mechanisms in untangling the combined stress tolerance in plants, and may also provide a promising venue for agronomists, physiologists, as well as molecular biologists.

CBL-interacting protein kinase 31 regulates rice resistance to blast disease by modulating cellular potassium levels

Rice blast disease caused by infection with Magnaporthe oryzae, a hemibiotrophic fungal pathogen, significantly reduces the yield production. However, the rice defense mechanism against blast disease remains elusive. To identify the genes involved in the regulation of rice defense to blast disease, dissociation (Ds) transposon tagging mutant lines were analyzed in terms of their response to M. oryzae isolate Guy11. Among them, CBL-interactingprotein kinase31 (CIPK31) mutants were more susceptible than wild-type plants to blast. The CIPK31 transcript was found to be insensitive to Guy11 infection, and the CIPK31-GFP was localized to the cytosol and nucleus. Overexpression of CIPK31 promoted rice defense to blast. Further analysis indicated that CIPK31 interacts with Calcineurin B-like 2 (CBL2) and CBL6 at the plasma membrane, and cbl2 mutants are more susceptible to blast compared with wild-type plants, suggesting that calcium signaling might partially through the CBL2-CIPK31 signaling regulate rice defense. Yeast two-hybrid results showed that AKT1-like (AKT1L), a potential potassium (K⁺) channel protein, interacted with CIPK31, and the K⁺ level was significantly lower in the cipk31 mutants than in the wild-type control. In addition, exogenous potassium application increased rice resistance to blast, suggesting that CIPK31 might interact with AKT1L to increase K⁺ uptake, thereby promoting resistance to blast. Taken together, the results presented here demonstrate that CBL2-CIPK31-AKT1L is a new signaling pathway that regulates rice defense to blast disease.

Sulfur Deprivation Modulates Salicylic Acid Responses via Nonexpressor of Pathogenesis-Related Gene 1 in Arabidopsis thaliana

Mineral nutrients are essential for plant growth and reproduction, yet only a few studies connect the nutritional status to plant innate immunity. The backbone of plant defense response is mainly controlled by two major hormones: salicylic acid (SA) and jasmonic acid (JA). This study investigated changes in the macronutrient concentration (deficiency/excess of nitrogen, phosphorus, potassium, magnesium, and sulfur) on the expression of PR1, a well-characterized marker in the SA-pathway, and PDF1.2 and LOX2 for the JA-pathway, analyzing plants carrying the promoter of each gene fused to GUS as a reporter. After histochemical GUS assays, we determined that PR1 gene was strongly activated in response to sulfur (S) deficiency. Using RT-PCR, we observed that the induction of PR1 depended on the function of Non-expressor of Pathogenesis-Related gene 1 (NPR1) and SA accumulation, as PR1 was not expressed in npr1-1 mutant and NahG plants under S-deprived conditions. Plants treated with different S-concentrations showed that total S-deprivation was required to induce SA-mediated defense responses. Additionally, bioassays revealed that S-deprived plants, induced resistance to the hemibiotrophic pathogen Pseudomonas syringae pv. DC3000 and increase susceptibility to the necrotrophic Botrytis cinerea. In conclusion, we observed a relationship between S and SA/JA-dependent defense mechanisms in Arabidopsis.

Impact of Phytophthora agathidicida infection on canopy and forest floor plant nutrient concentrations and fluxes in a kauri-dominated forest

Kauri dieback, caused by Phytophthora agathidicida, is a biotic disturbance that poses a recent threat to the survival of kauri (Agathis australis) forests in New Zealand. Previous studies have shown that throughfall and stemflow play an important role in the kauri forests' internal nutrient cycle. However, the effects of P. agathidicida infection on canopy and forest floor nutrient fluxes in kauri forests remain unknown. Here, we measured throughfall, stemflow and forest floor water yield, nutrient (potassium, calcium, magnesium, manganese, silicon, sulfur, sodium, iron) concentrations and fluxes of ten kauri trees differing in soil P. agathidicida DNA concentration, and health status. We did not observe an effect of soil P. agathidicida DNA concentration on throughfall, stemflow, and forest floor water yield. Throughfall and forest floor nutrient concentrations and fluxes decreased (up to 50%) with increasing soil P. agathidicida DNA concentration. We found significant effects on potassium and manganese fluxes in throughfall; calcium and silicon fluxes in forest floor leachate. A decline in canopy and forest floor nutrient fluxes may result in soil nutrient imbalances, which in turn may negatively impact forest productivity and may increase the susceptibility of trees to future pathogen infection in these ecologically unique kauri forests. Given our findings and the increasing spread of Phytophthora species worldwide, research on the underlying physiological mechanisms linking dieback and plant-soil nutrient fluxes is critical.

Conventional Soil Management May Promote Nutrients That Lure an Insect Pest to a Toxic Crop

Slow and consistent nutrient release by organic fertilizers can improve plant nutrient balance and defenses, leading to herbivore avoidance of organically managed crops in favor of conventional crops with weaker defenses. We propose that this relative attraction to conventional plants, coupled with the use of genetically modified, insecticidal crops (Bt), has created an unintentional attract-and-kill system. We sought to determine whether Bt and non-Bt corn Zea mays L. plants grown in soil collected from five paired organic and conventional fields differed in attractiveness to European corn borer [Ostrinia nubilalis (Hübner)] moths, by conducting ovipositional choice and flight tunnel assays. We then examined the mechanisms driving the observed differences in attraction by comparing soil nutrient profiles, soil microbial activity, plant nutrition, and plant volatile profiles. Finally, we assessed whether European corn borer abundance near corn fields differed based on soil management. European corn borer preferred plants grown in conventional soil but did not discriminate between Bt and non-Bt corn. Organic management and more alkaline soil were associated with an increased soil magnesium:potassium ratio, which increased plant magnesium, and were linked to reduced European corn borer oviposition. There was an inconsistent trend for higher European corn borer moth activity near conventional fields. Our results extend the mineral balance hypothesis describing conventional plant preference by showing that it can also improve attraction to plants with genetically inserted toxins. Unintentional attract (to conventional) and (Bt) kill is a plausible scenario for pest declines in response to Bt corn adoption, but this effect may be obscured by variation in other management practices and landscape characteristics.

The cross-kingdom roles of mineral nutrient transporters in plant-microbe relations

The regulation of plant physiology by plant mineral nutrient transporter (MNT) is well understood. Recently, the extensive characterization of beneficial and pathogenic plant-microbe interactions has defined the roles for MNTs in such relationships. In this review, we summarize the roles of diverse nutrient transporters in the symbiotic or pathogenic relationships between plants and microorganisms. In doing so, we highlight how MNTs of plants and microbes can act in a coordinated manner. In symbiotic relationships, MNTs play key roles in the establishment of the interaction between the host plant and rhizobium or mycorrhizae as well in the subsequent coordinated transport of nutrients. Additionally, MNTs may also regulate the colonization or degeneration of symbiotic microorganisms by reflecting the nutrient status of the plant and soil. This allows the host plant obtain nutrients from the soil in the most optimal manner. With pathogenic-interactions, MNTs influence pathogen proliferation, the efficacy of the host's biochemical defense and related signal transduction mechanisms. We classify the MNT effects in plant-pathogen interactions as either indirect by influencing the nutrient status and fitness of the pathogen, or direct by initiating host defense mechanisms. While such observations indicate the fundamental importance of MNTs in governing the interactions with a range of microorganisms, further work is needed to develop an integrative understanding of their functions.

FA, Sandoval F. JA. A Medium-Term Field Experiment to Study the Effect of Managing Soil Chemical Properties on Fusarium Wilt in Banana (Musa AAA)

Fusarium oxysporum f. sp. cubense (Foc) is a soil-borne fungus causing Fusarium wilt (FW) in banana. It is practically impossible to eradicate Foc in soils. Our understanding of soil–Foc–banana interactions is hampered by inconsistent research results caused by agro-ecological variability and the complexity of the soil system. This study aimed to evaluate the options to manage soil chemical properties to reduce disease expression and maintain banana production. The expression of FW (Foc Race 1) and the agronomic performance of the Gros Michel (Musa AAA) banana were evaluated in two medium-term factorial field experiments at representative locations in the Costa Rican banana region. In the experiments, five soil chemical properties (pH, N, Ca, Mg, and Mn) were managed to achieve a low and a high level. Plant mortality caused by FW, soil fertility, plant nutrition, and agronomic performance were monitored during four crop cycles. After the first crop cycle, the treatments started to present differences in plant mortality. There was a significant rise of plant mortality after the second crop cycle resulting in a cumulative plant mortality exceeding 60% in both experiments. A lower soil pH consistently resulted in significantly higher plant mortality. The interactions between soil properties (pH-N, pH-CaMg, pH-Mn, N-Mn, and CaMg-Mn) also influenced plant mortality. Soil N was the most significant treatment affecting leaf nutrient concentrations, bunch weight, and clusters per bunch. The experiments confirmed the potential role of soil management in FW expression in banana. Our results suggest that the management of soil chemical properties in the conditions here studied may help to reduce the expression rate of FW, but not to control the disease in the long run.

Enterobacter hormaechei (MF957335) enhanced yield, disease and salinity tolerance in tomato

Soil salinity is one of the major limiting factors for poor crop yield in the world. Increasing salinity in the soil is a challenge for agriculture. In the recent past, plant growth-promoting rhizobacteria (PGPR) are being used to enhance plant growth in various conditions. However, the saline-tolerant PGPR are of great use for plant growth under saline condition. In the present study, saline-tolerant E. hormaechei (MF957335) was isolated from saline water. E. hormaechei (MF957335) was tested for its potassium and calcium solubilizing efficiency using Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM-EDX). E. hormaechei (MF957335) and K-Feldspar treatments significantly increased plant growth as compared to untreated plants (negative control). E. hormaechei (MF957335) significantly increased fresh biomass, shoot and root length of tomato plants. Among all the NaCl treatments, maximum fruits (9.66) were achieved in 250 mM NaCl + E. hormaechei treatment. Similar results with increased fruit numbers were obtained in K-Feldspar-treated plants. Apart from the plant growth, fresh biomass and fruit numbers, tomatoes from K-Feldspar-treated plants were large, fleshy and deep red colored. The study could demonstrate bioavailability of potassium from K-feldspar for tomato cultivation. Control plants tomato were small, non-fleshy, yellowish red, and infected with calcium deficiency disease blossom-end rot. The present study demonstrates the role of E. hormaechei (MF957335) in plant growth, yield promotion and disease tolerance by potassium and calcium solubilization, respectively. The study showed that E. hormaechei (MF957335) could be applied to saline and non-saline soils to enhance tomato yield.

Effect of maternal infection on progeny growth and resistance mediated by maternal genotype and nutrient availability

Maternal effects of pathogen infection on progeny development and disease resistance may be adaptive and have important consequences for population dynamics. However, these effects are often context-dependent and examples of adaptive transgenerational responses from perennials are scarce, although they may be a particularly important mechanism generating variation in the offspring of long-lived species.Here, we studied the effect of maternal infection of Plantago lanceolata by Podosphaera plantaginis, a fungal parasite, on the growth, flower production and resistance of the progeny of six maternal genotypes in nutrient-rich and nutrient-poor environments. For this purpose, we combined a common garden study with automated phenotyping measurements of early life stages, and an inoculation experiment.Our results show that the effects of infection on the mother plants transcend to impact their progeny. Although maternal infection decreased total leaf and flower production of the progeny by the end of the growing season, it accelerated early growth and enhanced resistance to the pathogen P. plantaginis.We also discovered that the effects of maternal infection affected progeny development and resistance through a three way-interaction between maternal genotype, maternal infection status and nutrient availability. Synthesis. Our results emphasize the importance of maternal effects mediated through genotypic and environmental factors in long-living perennials and suggest that maternal infection can create a layer of phenotypic diversity in resistance. These results may have important implications for both epidemiological and evolutionary dynamics of host-parasite interactions in the wild.

Potassium Control of Plant Functions: Ecological and Agricultural Implications

Potassium, mostly as a cation (K+), together with calcium (Ca2+) are the most abundant inorganic chemicals in plant cellular media, but they are rarely discussed. K+ is not a component of molecular or macromolecular plant structures, thus it is more difficult to link it to concrete metabolic pathways than nitrogen or phosphorus. Over the last two decades, many studies have reported on the role of K+ in several physiological functions, including controlling cellular growth and wood formation, xylem-phloem water content and movement, nutrient and metabolite transport, and stress responses. In this paper, we present an overview of contemporary findings associating K+ with various plant functions, emphasizing plant-mediated responses to environmental abiotic and biotic shifts and stresses by controlling transmembrane potentials and water, nutrient, and metabolite transport. These essential roles of K+ account for its high concentrations in the most active plant organs, such as leaves, and are consistent with the increasing number of ecological and agricultural studies that report K+ as a key element in the function and structure of terrestrial ecosystems, crop production, and global food security. We synthesized these roles from an integrated perspective, considering the metabolic and physiological functions of individual plants and their complex roles in terrestrial ecosystem functions and food security within the current context of ongoing global change. Thus, we provide a bridge between studies of K+ at the plant and ecological levels to ultimately claim that K+ should be considered at least at a level similar to N and P in terrestrial ecological studies.

The effect of potassium fertilization on the metabolite profile of tomato fruit (Solanum lycopersicum L.)

The macronutrient potassium (K) has vital physiological functions in plants and its availability can strongly impact quality of crops like tomato. The impact of K nutrition on conventional tomato fruit quality parameters has been described several times, but detailed investigations on the effect of K supply on the fruit metabolite profile are still rare. To fill this gap, we investigated the influence of K fertilization on the metabolite profile of tomato fruits. For this purpose, an outdoor pot experiment with three different cocktail tomato cultivars was performed. A fertilization regimen with five K levels was applied, ranging from deficiency to sufficient supply. Fruit samples were analyzed by untargeted GC×GC-MS to cover the primary metabolite profile as well as some secondary metabolites. As verified using ICP-OES, fruit K content was highly proportional to the supplied amount of K. At the metabolite profile level, the most prominent and cultivar-independent effect of increased K fertilization was the rise of tricarboxylic acid (TCA) cycle intermediates. Further effects were more cultivar-specific, for example an increase of the mobile nitrogen pool (e.g. amines like putrescine and amides like asparagine), changes in the profile of minor sugars (especially disaccharides) as well as higher levels of some secondary metabolites. Pronounced response patterns were mainly observed in the cultivars Primavera and Yellow Submarine that were recently characterized as higher yielding, demanding a stronger consideration of cultivar differences in future studies.

Lowering Nitrogen and Increasing Potassium Application Level Can Improve the Yield and Quality of Panax notoginseng

Excessive nitrogen (N) application and potassium (K) supplement deficiency is a common problem in Panax notoginseng cultivation. However, synergistic effects of lowering N and increasing K application on yield and quality of P. notoginseng have not been reported. Field experiments in two locations with different N and K combined application were conducted to study the effects on yield and quality. Then, the saponin accumulation mechanisms were explored by pot and hydroponic culture with 2- or 3-year-old seedlings. The investigation showed that 70% of P. notoginseng cultivation fields reached abundant levels of total nitrogen (TN) but had deficient levels of total potassium (TK), which may be detrimental to balance the N/K uptake of P. notoginseng. Moreover, the average biomass was 18.9 g, and P. notoginseng saponin (PNS) content was 6.95%; both were influenced by the N/K values of P. notoginseng. The field experiments indicated that compared to the conventional N and K application (N:K = 2:1), lowering N and increasing K application (N:K = 1:2) decreased root rot rate by 36.4-46.1% and increased survival rate, root biomass, and yield, as well as PNS content by 17.9-18.3, 5.7-32.9, 27.8-57.1, and 5-10%, respectively. The mechanism of lowering N and increasing K application on the PNS content improving was due to the decreasing of N/K value, which promoted photosynthesis, sugar accumulation, and the expression of saponin biosynthesis genes. Therefore, lowering N and increasing K application to the ratio of 1:2 would have great potential to improve the synergistic effect on yield and quality of P. notoginseng cultivation.

Soil fungal and bacterial communities in southern boreal forests of the Greater Khingan Mountains and their relationship with soil properties

Little is known about the relationship between soil microbial communities and soil properties in southern boreal forests. To further our knowledge about that relationship, we compared the soil samples in southern boreal forests of the Greater Khingan Mountains—the southernmost boreal forest biome in the world. The forests can be divided into boardleaf forests dominated by birch (Betula platyphylla) or aspen (Populus davidiana) and coniferous forests dominated by larch (Larix gmelinii) or pine (Pinus sylvestris var. mongolica). Results suggested different soil microbial communities and soil properties between these southern boreal forests. Soil protease activity strongly associated with soil fungal communities in broadleaf and coniferous forests (p < 0.05), but not with soil bacterial communities (p > 0.05). Soil ammonium nitrogen and total phosphorus contents strongly associated with soil fungal and bacterial communities in broadleaf forests (p < 0.05), but not in coniferous forests (p > 0.05). Soil potassium content demonstrated strong correlations with both soil fungal and bacterial communities in broadleaf and coniferous forests (p < 0.05). These results provide evidence for different soil communities and soil properties in southern boreal forest, and further elucidate the explicit correlation between soil microbial communities and soil properties in southern boreal forests.

Plasmopara viticola infection affects mineral elements allocation and distribution in Vitis vinifera leaves

Plasmopara viticola is one of the most important pathogens infecting Vitis vinifera plants. The interactions among P. viticola and both susceptible and resistant grapevine plants have been extensively characterised, at transcriptomic, proteomic and metabolomic levels. However, the involvement of plants ionome in the response against the pathogen has been completely neglected so far. Therefore, this study was aimed at investigating the possible role of leaf ionomic modulation during compatible and incompatible interactions between P. viticola and grapevine plants. In susceptible cultivars, a dramatic redistribution of mineral elements has been observed, thus uncovering a possible role for mineral nutrients in the response against pathogens. On the contrary, the resistant cultivars did not present substantial rearrangement of mineral elements at leaf level, except for manganese (Mn) and iron (Fe). This might demonstrate that, resistant cultivars, albeit expressing the resistance gene, still exploit a pathogen response mechanism based on the local increase in the concentration of microelements, which are involved in the synthesis of secondary metabolites and reactive oxygen species. Moreover, these data also highlight the link between the mineral nutrition and plants' response to pathogens, further stressing that appropriate fertilization strategies can be fundamental for the expression of response mechanisms against pathogens.

Vitamin E Is Superior to Vitamin C in Delaying Seedling Senescence and Improving Resistance in Arabidopsis Deficient in Macro-Elements

Nitrogen (N), phosphorus (P), and potassium (K) are three essential macro-elements for plant growth and development. Used to improve yield in agricultural production, the excessive use of chemical fertilizers often leads to increased production costs and ecological environmental pollution. Vitamins C and E are antioxidants that play an important role in alleviating abiotic stress. However, there are few studies on alleviating oxidative stress caused by macro-element deficiency. Here, we used Arabidopsis vitamin E synthesis-deficient mutant vte4 and vitamin C synthesis-deficient mutant vtc1 on which exogenous vitamin E and vitamin C, respectively, were applied at the bolting stage. In the deficiency of macro-elements, the Arabidopsis chlorophyll content decreased, malondialdehyde (MDA) content and relative electric conductivity increased, and reactive oxygen species (ROS) accumulated. The mutants vtc1 and vte4 are more severely stressed than the wild-type plants. Adding exogenous vitamin E was found to better alleviate stress than adding vitamin C. Vitamin C barely affected and vitamin E significantly inhibited the synthesis of ethylene (ETH) and jasmonic acid (JA) genes, thereby reducing the accumulation of ETH and JA that alleviated the senescence caused by macro-element deficiency at the later stage of bolting in Arabidopsis. A deficiency of macro-elements also reduced the yield and germination rate of the seeds, which were more apparent in vtc1 and vte4, and adding exogenous vitamin C and vitamin E, respectively, could restore them. This study reported, for the first time, that vitamin E is better than vitamin C in delaying seedling senescence caused by macro-element deficiency in Arabidopsis.

Performance Comparison of Eichhornia crassipes and Salvinia natans on Azo-Dye (Eriochrome Black T) Phytoremediation

Organic pollutants, such as dyes, have a negative effect on the aqueous environment, therefore, their elimination from water bodies is a high priority. In this work, Eichhornia crassipes and Salvinia natans, both model plants with high phytoremediation efficiency, were exposed to various concentrations (Ci = 50–500 mg/L) of Eriochrome Black T (EBT). Their capacity to assimilate EBT was studied for 16 days of exposure, similar to natural conditions and by spectrophotometric monitoring of the dye concentration (EE. crassipes; 150 mg/L = 33%; ES. natans; 150 mg/L = 71.5%). The changes of the experimental parameters (pH—equalised by day 5, temperature, humidity, light intensity) were followed, and plant growth and biochemical responses to toxic stress effects (photosynthetic pigments, Energy-dispersive X-ray spectroscopy (EDX)—decreased effect of P, Mg, Ca, S and K, Scanning electron microscopy (SEM), defense enzyme) were examined. Furthermore, changes in oxidative- and photo-degradation of EBT in time and the solid-state properties (SEM, EDX, Fourier-transform infrared spectroscopy-FTIR) of the dye were investigated. Our results demonstrate that, despite the toxic stress, both species succeeded in reducing the dye-concentration of the water and S. natans proved to be more efficient in binding and removing organic dyes. With our findings, we proved that both plants alleviated the abiotic stress of dye contamination.

Nitrate Stabilizes the Rhizospheric Fungal Community to Suppress Fusarium Wilt Disease in Cucumber

Nitrogen forms can regulate soil-borne Fusarium wilt suppression, but the related mechanisms are largely unknown, especially possible action via the rhizospheric microbial community. Soil analysis, MiSeq high-throughput sequencing analysis, community diversity, and network analysis were used to characterize the impact of different nitrogen forms (nitrate and ammonium) on rhizospheric fungal communities and the contribution of nitrate to the suppression to Fusarium oxysporum f. sp. cucumerinum compared with ammonium. Nitrate-grown cucumber showed a lower disease index and F. oxysporum f. sp. cucumerinum abundance in the rhizosphere. In comparisons with ammonium nutrients, nitrate-fed plants maintained a higher soil rhizosphere pH, microbial biomass carbon content, microbial biomass nitrogen content, as well as fungal community richness and diversity following F. oxysporum f. sp. cucumerinum incubation. All these factors were negatively related with disease index. Network analysis showed fewer nodes and edges in the ammonium treatments compared with nitrate treatments. The relative abundance of Pathotroph-Saprotroph, Pathotroph-Saprotroph-Symbiotroph, and Saprotroph fungi explained 82% of the variability of rhizosphere F. oxysporum f. sp. cucumerinum abundance. In conclusion, after pathogen inoculation under nitrate nutrition, the less-affected microbial composition, community diversity, and community internal relations, which resulted from the more diverse and robust microbial population, potentially contributed to greater Fusarium wilt suppression.

Estimation of leaf nutrition status in degraded vegetation based on field survey and hyperspectral data

Timely monitoring of global plant biogeochemical processes demands fast and highly accurate estimation of plant nutrition status, which is often estimated based on hyperspectral data. However, few such studies have been conducted on degraded vegetation. In this study, complete combinations of either original reflectance or first-order derivative spectra have been developed to quantify leaf nitrogen (N), phosphorus (P), and potassium (K) contents of tree, shrub, and grass species using hyperspectral datasets from light, moderate, and severely degraded vegetation sites in Helin County, China. Leaf N, P, and K contents were correlated to identify suitable combinations. The most effective combinations were those of reflectance difference (Dij), normalized differences (ND), first-order derivative (FD), and first-order derivative difference (FD(D)). Linear regression analysis was used to further optimize sensitive band-based combinations, which were compared with 43 frequently used empirical spectral indices. The proposed hyperspectral indices were shown to effectively quantify leaf N, P, and K content (R2 > 0.5, p < 0.05), confirming that hyperspectral data can be potentially used for fine scale monitoring of degraded vegetation.

Drones: Innovative Technology for Use in Precision Pest Management

Arthropod pest outbreaks are unpredictable and not uniformly distributed within fields. Early outbreak detection and treatment application are inherent to effective pest management, allowing management decisions to be implemented before pests are well-established and crop losses accrue. Pest monitoring is time-consuming and may be hampered by lack of reliable or cost-effective sampling techniques. Thus, we argue that an important research challenge associated with enhanced sustainability of pest management in modern agriculture is developing and promoting improved crop monitoring procedures. Biotic stress, such as herbivory by arthropod pests, elicits physiological defense responses in plants, leading to changes in leaf reflectance. Advanced imaging technologies can detect such changes, and can, therefore, be used as noninvasive crop monitoring methods. Furthermore, novel methods of treatment precision application are required. Both sensing and actuation technologies can be mounted on equipment moving through fields (e.g., irrigation equipment), on (un)manned driving vehicles, and on small drones. In this review, we focus specifically on use of small unmanned aerial robots, or small drones, in agricultural systems. Acquired and processed canopy reflectance data obtained with sensing drones could potentially be transmitted as a digital map to guide a second type of drone, actuation drones, to deliver solutions to the identified pest hotspots, such as precision releases of natural enemies and/or precision-sprays of pesticides. We emphasize how sustainable pest management in 21st-century agriculture will depend heavily on novel technologies, and how this trend will lead to a growing need for multi-disciplinary research collaborations between agronomists, ecologists, software programmers, and engineers.

Arbuscular mycorrhiza and environmentally biochemicals enhance the nutritional status of Helianthus tuberosus and induce its resistance against Sclerotium rolfsii

Chemical fungicides are effective tools in controlling plant pathogens; however, these chemicals can, on the other hand, distress the ecosystem. Accordingly, the current research investigates the potentiality of substituting traditional chemical fungicides by inducing plant resistance against infection with soil-born pathogens i.e. Sclerotium rolfsii in the presence of mycorrhizae (AMF) as plant inoculants and one of the following amendments: humic acid, sulphex (a mixture of canola oil and diluted sulphuric acid) and paclobutrazol (ABZ). To attain the abovementioned objective, a field (mildly infected with S. rolfsii) was cultivated with Helianthus tuberosus (a perennial plant belongs to the Asteraceae family) for two successive seasons (2014 and 2015) and the above-mentioned treatments were tested for their feasibilities in controlling S. rolfsii infection against the chemical fungicide "Vitavax-200" either solely or in combinations in a complete randomized block design. Inoculating plants with AMF or amending soils with either humic acid, Sulphex or ABZ solely increased significantly the activities of plant defense enzymes by approximately 1.5-2.1 folds higher than the control treatment. These treatments also improved NPK availability in soil and; hence, increased their contents within plant tubers. Consequently, these treatments decreased the disease incidence and severity caused by S. rolfsii while improved shoot biomass and tuber yield. In spite of that, these results stood below the prospective of the fungicide treatment. The integrated treatments i.e. "humic acid + AMF", "Sulphex + AMF" and "ABZ + AMF" caused further significant improvements in both NPK availabilities in soil and plant areal bio-masses. This probably induced further plant resistance against the investigated soil-borne pathogen while recorded insignificant variations in disease incidence and severity when compared with the fungicide treatment. Moreover, the integrated treatments increased the tuber yields beyond those attained for the fungicide treatment. Accordingly, such integrated strategies can completely substitute the chemical fungicides; thus, minimize their negative impacts on the ecosystem.

Potassium deficiency aggravates yield loss in rice by restricting the translocation of non-structural carbohydrates under Sarocladium oryzae infection condition

Sheath rot disease (ShR) caused by Sarocladium oryzae (S. oryzae) infection is an emerging disease that causes severe yield loss by restricting the translocation of non-structural carbohydrates (NSC). Potassium (K) nutrition plays a critical role in disease resistance and the exportation of NSC. However, the physiological mechanisms of K with respect to ShR have not been thoroughly elucidated to date. The objectives of this study were to reveal the mechanisms by which K increases ShR resistance by regulating NSC translocation of rice, therefore, a field experiment combined with an inoculation experiment was conducted. We demonstrate that ShR disease incidence and disease index decreased dramatically with an increasing K application. K deficiency sharply induced the accumulation of NSC in the flag leaf (FL) and flag leaf sheath (FLS) under S. oryzae infection condition, which reduced the contribution of transferred NSC to final yield. A permutational multivariate analysis showed that K deficiency had a greater (49.0%, P < 0.001) effect on the NSC content variation in FL than that of S. oryzae infection (15.0%, P < 0.001). S. oryzae infection dramatically increased the difference in apparent transferred mass of NSC and cell membrane injury of diseased organs between K-deficient and K-sufficient rice. Finally, we demonstrate that cell membrane injury was a limiting factor imposed by K deficiency, which restricts the export of NSC from source organs. This work highlights the importance of K in improving ShR resistance by regulating NSC translocation (particularly the stem NSC).

Secondary metabolites profile and physiological leaf traits in wild and cultivated Corylus avellana under different nutritional status

Leaf secondary metabolites production and physiological leaf traits were analyzed in Corylus avellana wild type (WT) and cultivar (cv. 'Tonda Gentile Trilobata', TGT) under different nutrient supplies. Three treatments were applied: control treatment with no fertilizer supply (WT_C and TGT_C), low nutrient treatment (WT_LN and TGT_LN) and high nutrient treatment (WT_HN and TGT_HN). The analysis of leaf extracts showed a higher concentration of Quercitrin and Myricitrin, with the highest concentrations of both the compounds in WT than TGT. This result can be related to the ecological role of flavonoids, including also antimicrobial properties, which resulted more useful in the understory forest form which hazelnut wild type originates. Therefore, their lower concentration in TGT can be relate to the genetic background of TGT cultivar with a lesser intrinsic need to produce such compounds and justified by a usual growth under more controlled environmental conditions, including also pest and disease control.

Potassium in Root Growth and Development

Potassium is an essential macronutrient that has been partly overshadowed in root science by nitrogen and phosphorus. The current boom in potassium-related studies coincides with an emerging awareness of its importance in plant growth, metabolic functions, stress tolerance, and efficient agriculture. In this review, we summarized recent progress in understanding the role of K+ in root growth, development of root system architecture, cellular functions, and specific plant responses to K+ shortage. K+ transport is crucial for its physiological role. A wide range of K+ transport proteins has developed during evolution and acquired specific functions in plants. There is evidence linking K+ transport with cell expansion, membrane trafficking, auxin homeostasis, cell signaling, and phloem transport. This places K+ among important general regulatory factors of root growth. K+ is a rather mobile element in soil, so the absence of systemic and localized root growth response has been accepted. However, recent research confirms both systemic and localized growth response in Arabidopsis thaliana and highlights K+ uptake as a crucial mechanism for plant stress response. K+-related regulatory mechanisms, K+ transporters, K+ acquisition efficiency, and phenotyping for selection of K+ efficient plants/cultivars are highlighted in this review.

A Role for Zinc in Plant Defense Against Pathogens and Herbivores

Pests and diseases pose a threat to food security, which is nowadays aggravated by climate change and globalization. In this context, agricultural policies demand innovative approaches to more effectively manage resources and overcome the ecological issues raised by intensive farming. Optimization of plant mineral nutrition is a sustainable approach to ameliorate crop health and yield. Zinc is a micronutrient essential for all living organisms with a key role in growth, development, and defense. Competition for Zn affects the outcome of the host-attacker interaction in both plant and animal systems. In this review, we provide a clear framework of the different strategies involving low and high Zn concentrations launched by plants to fight their enemies. After briefly introducing the most relevant macro- and micronutrients for plant defense, the functions of Zn in plant protection are summarized with special emphasis on superoxide dismutases (SODs) and zinc finger proteins. Following, we cover recent meaningful studies identifying Zn-related passive and active mechanisms for plant protection. Finally, Zn-based strategies evolved by pathogens and pests to counteract plant defenses are discussed.

The Hot QTL Locations for Potassium, Calcium, and Magnesium Nutrition and Agronomic Traits at Seedling and Maturity Stages of Wheat under Different Potassium Treatments

Potassium (K) is one of the most important mineral nutrients for wheat. In this study, the effects of low K (LK) treatments and the quantitative trait loci (QTLs) for K, calcium (Ca), and magnesium (Mg) use efficiency traits, both at the seedling and maturity stages of wheat, were investigated. The set of “Tainong 18 × Linmai 6” recombinant inbred lines (RILs) were used to identify the QTLs under different K treatments using hydroponic culture and field trials. The majority of K concentrations and content-related traits at seedling and maturity stages decreased with reduced K supply, but the K use efficiency-related traits increased. In contrast, with reduced K supply, the contents of Ca and Mg increased, while the Ca and Mg use efficiency decreased. A total of 217 QTLs for seedling traits and 89 QTLs for adult traits were detected. Four relatively high-frequency QTLs (RHF-QTLs) and 18 QTL clusters (colocation of QTLs for more than two traits) were detected. Eight clusters were detected for K-, Ca-, and Mg-related traits simultaneously. This means that these traits might be controlled by the same QTL. In addition, we highlight that 4B might be an important chromosome regulating the nutrition of K, Ca, and Mg in wheat. The 4B chromosome and four hot QTL clusters, which located 45 QTLs, might be important potential targets for further investigation.

Grapevine trunk diseases under thermal and water stresses

Heat and water stresses, individually or combined, affect both the plant (development, physiology, and production) and the pathogens (growth, morphology, dissemination, distribution, and virulence). The grapevine response to combined abiotic and biotic stresses is complex and cannot be inferred from the response to each single stress. Several factors might impact the response and the recovery of the grapevine, such as the intensity, duration, and timing of the stresses. In the heat/water stress-GTDs-grapevine interaction, the nature of the pathogens, and the host, i.e., the nature of the rootstock, the cultivar and the clone, has a great importance. This review highlights the lack of studies investigating the response to combined stresses, in particular molecular studies, and the misreading of the relationship between rootstock and scion in the relationship GTDs/abiotic stresses. Grapevine trunk diseases (GTDs) are one of the biggest threats to vineyard sustainability in the next 30 years. Although many treatments and practices are used to manage GTDs, there has been an increase in the prevalence of these diseases due to several factors such as vineyard intensification, aging vineyards, or nursery practices. The ban of efficient treatments, i.e., sodium arsenite, carbendazim, and benomyl, in the early 2000s may be partly responsible for the fast spread of these diseases. However, GTD-associated fungi can act as endophytes for several years on, or inside the vine until the appearance of the first symptoms. This prompted several researchers to hypothesise that abiotic conditions, especially thermal and water stresses, were involved in the initiation of GTD symptoms. Unfortunately, the frequency of these abiotic conditions occurring is likely to increase according to the recent consensus scenario of climate change, especially in wine-growing areas. In this article, following a review on the impact of combined thermal and water stresses on grapevine physiology, we will examine (1) how this combination of stresses might influence the lifestyle of GTD pathogens, (2) learnings from grapevine field experiments and modelling aiming at studying biotic and abiotic stresses, and (3) what mechanistic concepts can be used to explain how these stresses might affect the grapevine plant status.

Differences in Distribution of Potassium-Solubilizing Bacteria in Forest and Plantation Soils in Myanmar

Potassium (K) has been recognized as an essential element in intensive agricultural production systems, and deficiency of K usually results in a decrease in crop yields. The utilization of potassium-solubilizing bacteria (KSB) to increase the soluble K content in soil has been regarded as a desirable pathway to increase plant yields. Following the inoculation of KSB in the soil, potassium can be released (in the form of K⁺) and consumed by plants. This study aims to investigate and compare the distribution characteristics of potassium-solubilizing bacteria between forest and plantation soils in Myanmar. In this study, 14 KSB strains were isolated from rhizosphere samples collected from forest soil, as well as fertilized rubber tree rhizosphere soil and fertilized bare soil from a plantation. Broadleaf forests with high levels of canopy cover mainly comprised the forest environment, and rubber trees were planted in the plantation environment. The Chao and abundance-based coverage estimator (ACE) indices showed that the microbial abundance of the plantation soil was higher than that of the forest soil. According to the Illumina MiSeq sequencing analysis results, the Shannon index of the forest soil was lower while the Simpson index was higher, which demonstrated that the microbial diversity of the forest soil was higher than that of the plantation soil. Potassium-solubilizing test results showed that the strains E, I, M, and N were the most effective KSB under liquid cultivation conditions. Additionally, KSB only accounted for less than 5.47% of the total bacteria detected in either of the sample types, and the distribution of dominant KSB varied with the soil samples. As another result, the abundance of Pseudomonas spp. in S1 was higher than in S2 and S3, indicating a negative impact on the growth of Pseudomonas in the fertilized rubber tree rhizosphere soil. The significance of our research is that it proves that the increasing use of KSB for restoring soil is a good way to reduce the use of chemical fertilizers, which could further provide a relatively stable environment for plant growth.

The combination of K+ deficiency with other environmental stresses: What is the outcome?

Potassium (K⁺ ) is a macronutrient known for its high mobility and positive charge, which allows efficient and fast control of the electrical balance and osmotic potential in plant cells. Such features allow K⁺ to remarkably contribute to plant stress adaptation. Some agricultural lands are deficient in K⁺ , imposing a stress that reduces crop yield and makes fertilization a common practice. However, individual stress conditions in the field are rare, and crops usually face a combination of different stresses. As plant response to a stress combination cannot always be deduced from individual stress action, it is necessary to gain insights into the specific mechanisms that connect K⁺ homeostasis with other stress effects to improve plant performance in the context of climate change. Surprisingly, plant responses to environmental stresses under a K⁺ -limiting scenario are poorly understood. In the present review, we summarize current knowledge and find substantial gaps regarding specific outcomes of K⁺ deficiency in addition to other environmental stresses. In this regard, combined nutrient deficiencies of K⁺ and other macronutrients are covered in the first part of the review and interactions arising from K⁺ deficiency with salinity, drought and biotic factors in the second part. Information available so far suggests a prominent role of potassium and nitrate transport systems and their regulatory proteins in the response of plants to several stress combinations. Thus, such molecular pathways, which are located at the crossroad between K⁺ homeostasis and environmental stresses, could be considered biotechnological targets in future studies.

Contrasting nutrient-disease relationships: Potassium gradients in barley leaves have opposite effects on two fungal pathogens with different sensitivities to jasmonic acid

Understanding the interactions between mineral nutrition and disease is essential for crop management. Our previous studies with Arabidopsis thaliana demonstrated that potassium (K) deprivation induced the biosynthesis of jasmonic acid (JA) and increased the plant's resistance to herbivorous insects. Here, we addressed the question of how tissue K affects the development of fungal pathogens and whether sensitivity of the pathogens to JA could play a role for the K-disease relationship in barley (Hordeum vulgare cv. Optic). We report that K-deprived barley plants showed increased leaf concentrations of JA and other oxylipins. Furthermore, a natural tip-to-base K-concentration gradient within leaves of K-sufficient plants was quantitatively mirrored by the transcript levels of JA-responsive genes. The local leaf tissue K concentrations affected the development of two economically important fungi in opposite ways, showing a positive correlation with powdery mildew (Blumeria graminis) and a negative correlation with leaf scald (Rhynchosporium commune) disease symptoms. B. graminis induced a JA response in the plant and was sensitive to methyl-JA treatment whereas R. commune initiated no JA response and was JA insensitive. Our study challenges the view that high K generally improves plant health and suggests that JA sensitivity of pathogens could be an important factor in determining the exact K-disease relationship.

Effects of Potassium Fertilizer Rates on Soybean Looper (Lepidoptera: Noctuidae) Development

Potassium (K) has an important impact on physiological and biochemical processes in plants. Soybean, Glycine max (L.) Merrill, requires high K availability for optimal yield. However, changes in nutrient availability in plants may also affect herbivore population size and/or development. Soybean looper, Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae), is one of the most destructive pests of soybean in the southern United States. In this study, we evaluated the effects of different K fertilization rates on soybean looper development, soybean seed weight, and soybean seed nutritional quality. Soybean plants were supplied with six different rates of K fertilizer (0, 33.6, 67.3, 100.9, 134.5, and 168.1 kg/ha as K2O). Soybean leaves were sampled at R1, R3, R5, and R6 stages and fed to soybean looper in laboratory bioassays. Soybean looper mortality, fecundity, and fertility were not significantly affected by feeding on leaf tissues of soybean treated with different potassium fertilizer rates. However, soybean looper consumed more leaf tissue and spent less time completing larval development when fed on foliage from treatments of 134.5 and 168.1 kg/ha. Pupal weight significantly increased at 134.5 and 168.1 kg/ha. There was no significant difference in percentage of protein, oil, and fiber in soybean seeds among six K fertilizer rates. Percentage of K in soybean seeds and 100 seed weight were significantly enhanced at 168.1 kg/ha. Nitrogen (N) content of foliage was not affected by applying K fertilizer at different rates. Our results indicate that higher K fertilizer rates can enhance soybean seed weight but also facilitate soybean looper development.

Canola Nutrition and Variety Affect Oviposition and Offspring Performance in the Generalist Herbivore, Mamestra configurata (Lepidoptera: Noctuidae)

Bertha armyworm Mamestra configurata Walker (Lepidoptera: Noctuidae) is a generalist herbivore that feeds on several crops in different plant families. Canola Brassica napus L. (Capparales: Brassicaceae) is one of the most favored host plants making the bertha armyworm a significant insect pest in the Canadian Prairie Provinces. The performance of the bertha armyworm on canola may vary with the quality of the canola plant. We tested the impact of plant nutrition and canola variety on oviposition and subsequent larval development of the bertha armyworm. A range of fertilization levels (0.0, 1.0, 3.0, and 5.0 g/pot) were applied to three different canola varieties: Clearfield 5535 CL, Roundup Ready hybrid 6060RR, and Q2. The total number of eggs laid on plants in a no-choice experiment increased with fertilizer level but a similar number of eggs were laid on plants that received moderate and high fertilizer treatments. Larvae reared on plants that received the moderate fertilizer application yielded heavier pupae than those reared on plants with low and high fertilizer treatments. Most eggs were laid on the Q2 variety when compared to Clearfield 5535 CL and Roundup Ready 6060 RR. Bertha armyworm females preferred to lay eggs on plants that received moderate or high fertilization over plants with the low fertilizer treatment. Plant leaf tissue nutrient content and plant growth were highest in plants that received moderate and high fertilizer treatment. We conclude that bertha armyworm oviposition behavior and larval performance are influenced by fertilizer treatment and canola variety.

Potassium-induced plant resistance against soybean cyst nematode via root exudation of phenolic acids and plant pathogen-related genes

Soybean cyst nematode (SCN) is a severe soil borne disease. The control of this disease is still a worldwide problem in agriculture. In this study, we found that application of potassium (K) fertilizer could decrease the occurrence of SCN at two field sites. Furthermore, the application of K could suppress Heterodera glycines with the activation of Phenylalanine Ammonia Lyase (PAL) and Polyphenol Oxidase (PPO) expression via pot experiments in a greenhouse. The release of cinnamic, ferulic and salicylic acids was significantly enhanced by K application of 3 mM, and each of three acids can dramatically constrain Heterodera glycines in vitro. This research indicated that K induce multiple mechanisms to improve the resistance of soybean against SCN and provide a new strategy to control SCN in fields with nutrient application.

The fungal pathogen Magnaporthe oryzae suppresses innate immunity by modulating a host potassium channel

Potassium (K⁺) is required by plants for growth and development, and also contributes to immunity against pathogens. However, it has not been established whether pathogens modulate host K⁺ signaling pathways to enhance virulence and subvert host immunity. Here, we show that the effector protein AvrPiz-t from the rice blast pathogen Magnaporthe oryzae targets a K⁺ channel to subvert plant immunity. AvrPiz-t interacts with the rice plasma-membrane-localized K⁺ channel protein OsAKT1 and specifically suppresses the OsAKT1-mediated K⁺ currents. Genetic and phenotypic analyses show that loss of OsAKT1 leads to decreased K⁺ content and reduced resistance against M. oryzae. Strikingly, AvrPiz-t interferes with the association of OsAKT1 with its upstream regulator, the cytoplasmic kinase OsCIPK23, which also plays a positive role in K⁺ absorption and resistance to M. oryzae. Furthermore, we show a direct correlation between blast disease resistance and external K⁺ status in rice plants. Together, our data present a novel mechanism by which a pathogen suppresses plant host immunity by modulating a host K⁺ channel.

Plant nutritional status can greatly influence plant immunity in response to pathogen invasion. Rice blast, a devastating rice disease caused by the hemibiotrophic fungus Magnaporthe oryzae, causes a significant reduction in yield and affects food security. In this study, we demonstrate that the M. oryzae secreted protein AvrPiz-t interacts with rice OsAKT1, a potassium (K⁺) channel protein, and suppresses OsAKT1-mediated inward K⁺ currents, possibly by competing with the OsAKT1 upstream regulator, OsCIPK23. We also show that both OsAKT1 and OsCIPK23 are required for K⁺ uptake and resistance against M. oryzae infection in rice. This study provides new insights into the molecular basis of pathogen-mediated perturbation of a plant nutrition pathway.

Potassium improves photosynthetic tolerance to and recovery from episodic drought stress in functional leaves of cotton (Gossypium hirsutum L.)

To investigate whether potassium (K) application enhances the potential of cotton (Gossypium hirsutum L.) plants to maintain physiological functions during drought and recovery, low K-sensitive (Siza 3) and -tolerant (Simian 3) cotton cultivars were exposed to three K rates (0, 150, and 300 K₂O kg ha^-1) and either well-watered conditions or severe drought stress followed by a recovery period. Under drought stress, cotton plants showed a substantial decline in leaf water potential, stomatal conductance, photosynthetic rate, and the maximum and actual quantum yield of PSII, resulting in greater non-photochemical quenching and lipid peroxidation as compared to well-watered plants. However, plants under K application not only showed less of a decline in these traits but also displayed greater potential to recover after rewatering as compared to the plants without K application. Plants receiving K application showed lower lipid peroxidation, higher antioxidant enzyme activities, and increased proline accumulation as compared to plants without K application. Significant relationships between rates of photosynthetic recovery and K application were observed. The cultivar Siza 3 exhibited a more positive response to K application than Simian 3. The results suggest that K application enhances the cotton plant's potential to maintain functionality under drought and facilitates recovery after rewatering.

MicroRNA-mediated responses to long-term magnesium-deficiency in Citrus sinensis roots revealed by Illumina sequencing

Background

Magnesium (Mg)-deficiency occurs most frequently in strongly acidic, sandy soils. Citrus are grown mainly on acidic and strong acidic soils. Mg-deficiency causes poor fruit quality and low fruit yield in some Citrus orchards. For the first time, we investigated Mg-deficiency-responsive miRNAs in ‘Xuegan’ (Citrus sinensis) roots using Illumina sequencing in order to obtain some miRNAs presumably responsible for Citrus Mg-deficiency tolerance.

Results

We obtained 101 (69) miRNAs with increased (decreased) expression from Mg-starved roots. Our results suggested that the adaptation of Citrus roots to Mg-deficiency was related to the several aspects: (a) inhibiting root respiration and related gene expression via inducing miR158 and miR2919; (b) enhancing antioxidant system by down-regulating related miRNAs (miR780, miR6190, miR1044, miR5261 and miR1151) and the adaptation to low-phosphorus (miR6190); (c) activating transport-related genes by altering the expression of miR6190, miR6485, miR1044, miR5029 and miR3437; (d) elevating protein ubiquitination due to decreased expression levels of miR1044, miR5261, miR1151 and miR5029; (e) maintaining root growth by regulating miR5261, miR6485 and miR158 expression; and (f) triggering DNA repair (transcription regulation) by regulating miR5176 and miR6485 (miR6028, miR6190, miR6485, miR5621, miR160 and miR7708) expression. Mg-deficiency-responsive miRNAs involved in root signal transduction also had functions in Citrus Mg-deficiency tolerance.

Conclusions

We obtained several novel Mg-deficiency-responsive miRNAs (i.e., miR5261, miR158, miR6190, miR6485, miR1151 and miR1044) possibly contributing to Mg-deficiency tolerance. These results revealed some novel clues on the miRNA-mediated adaptation to nutrient deficiencies in higher plants.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3999-5) contains supplementary material, which is available to authorized users.

Ecology and Genomic Insights into Plant-Pathogenic and Plant-Nonpathogenic Endophytes

Plants are colonized on their surfaces and in the rhizosphere and phyllosphere by a multitude of different microorganisms and are inhabited internally by endophytes. Most endophytes act as commensals without any known effect on their plant host, but multiple bacteria and fungi establish a mutualistic relationship with plants, and some act as pathogens. The outcome of these plant-microbe interactions depends on biotic and abiotic environmental factors and on the genotype of the host and the interacting microorganism. In addition, endophytic microbiota and the manifold interactions between members, including pathogens, have a profound influence on the function of the system plant and the development of pathobiomes. In this review, we elaborate on the differences and similarities between nonpathogenic and pathogenic endophytes in terms of host plant response, colonization strategy, and genome content. We furthermore discuss environmental effects and biotic interactions within plant microbiota that influence pathogenesis and the pathobiome.

Induction of Barley Silicon Transporter HvLsi1 and HvLsi2, increased silicon concentration in the shoot and regulated Starch and ABA Homeostasis under Osmotic stress and Concomitant Potassium Deficiency

Drought is one of the major stress factors reducing cereal production worldwide. There is ample evidence that the mineral nutrient status of plants plays a critical role in increasing plant tolerance to different biotic and abiotic stresses. In this regard, the important role of various nutrients e.g., potassium (K) or silicon (Si) in the mitigation of different stress factors, such as drought, heat or frost has been well documented. Si application has been reported to ameliorate plant nutrient deficiency. Here, we used K and Si either solely or in combination to investigate whether an additive positive effect on barley growth can be achieved under osmotic stress and which mechanisms contribute to a better tolerance to osmotic stress. To achieve this goal, barley plants were subjected to polyethylene glycol (PEG)-induced osmotic stress under low or high K supply and two Si regimes. The results showed that barley silicon transporters HvLsi1 and HvLsi2 regulate the accumulation of Si in the shoot only when plant suffered from K deficiency. Si, in turn, increased the starch level under both osmotic stress and K deficiency and modulated the glycolytic and TCA pathways. Hormone profiling revealed that the beneficial effect of Si is most likely mediated also by ABA homeostasis and active cytokinin isopentenyl adenine (iP). We conclude that Si may effectively improve stress tolerance under K deficient condition in particular when additional stress like osmotic stress interferes.

Higher Fertilizer Inputs Increase Fitness Traits of Brown Planthopper in Rice

Rice (Oryza sativa L.) is the primary staple food source for more than half of the world's population. In many developing countries, increased use of fertilizers is a response to increase demand for rice. In this study, we investigated the effects of three principal fertilizer components (nitrogen, phosphorus and potassium) on the development of potted rice plants and their effects on fitness traits of the brown planthopper (BPH) [Nilaparvata lugens (Stål) (Homoptera: Delphacidae)], which is a major pest of rice in Bangladesh and elsewhere. Compared to low fertilizer inputs, high fertilizer treatments induced plant growth but also favored BPH development. The BPH had higher survival, developed faster, and the intrinsic rate of natural increase (r _m ) was higher on well-fertilized than under-fertilized plants. Among the fertilizer inputs, nitrogen had the strongest effect on the fitness traits of BPH. Furthermore, both the "Plant vigor hypothesis" and the "Plant stress hypothesis" were supported by the results, the former hypothesis more so than the latter. These hypotheses suggest that the most suitable/attractive hosts for insect herbivores are the most vigorous plants. Our findings emphasized that an exclusive focus on yield increases through only enhanced crop fertilization may have unforeseen, indirect, effects on crop susceptibility to pests, such as BPH.

The receptor-like pseudokinase MRH1 interacts with the voltage-gated potassium channel AKT2

The potassium channel AKT2 plays important roles in phloem loading and unloading. It can operate as inward-rectifying channel that allows H+-ATPase-energized K+ uptake. Moreover, through reversible post-translational modifications it can also function as an open, K+-selective channel, which taps a 'potassium battery', providing additional energy for transmembrane transport processes. Knowledge about proteins involved in the regulation of the operational mode of AKT2 is very limited. Here, we employed a large-scale yeast two-hybrid screen in combination with fluorescence tagging and null-allele mutant phenotype analysis and identified the plasma membrane localized receptor-like kinase MRH1/MDIS2 (AT4G18640) as interaction partner of AKT2. The phenotype of the mrh1-1 knockout plant mirrors that of akt2 knockout plants in energy limiting conditions. Electrophysiological analyses showed that MRH1/MDIS2 failed to exert any functional regulation on AKT2. Using structural protein modeling approaches, we instead gathered evidence that the putative kinase domain of MRH1/MDIS2 lacks essential sites that are indispensable for a functional kinase suggesting that MRH1/MDIS2 is a pseudokinase. We propose that MRH1/MDIS2 and AKT2 are likely parts of a bigger protein complex. MRH1 might help to recruit other, so far unknown partners, which post-translationally regulate AKT2. Additionally, MRH1 might be involved in the recognition of chemical signals.

LSU network hubs integrate abiotic and biotic stress responses via interaction with the superoxide dismutase FSD2

In natural environments, plants often experience different stresses simultaneously, and adverse abiotic conditions can weaken the plant immune system. Interactome mapping revealed that the LOW SULPHUR UPREGULATED (LSU) proteins are hubs in an Arabidopsis protein interaction network that are targeted by virulence effectors from evolutionarily diverse pathogens. Here we show that LSU proteins are up-regulated in several abiotic and biotic stress conditions, such as nutrient depletion or salt stress, by both transcriptional and post-translational mechanisms. Interference with LSU expression prevents chloroplastic reactive oxygen species (ROS) production and proper stomatal closure during sulphur stress. We demonstrate that LSU1 interacts with the chloroplastic superoxide dismutase FSD2 and stimulates its enzymatic activity in vivo and in vitro. Pseudomonas syringae virulence effectors interfere with this interaction and preclude re-localization of LSU1 to chloroplasts. We demonstrate that reduced LSU levels cause a moderately enhanced disease susceptibility in plants exposed to abiotic stresses such as nutrient deficiency, high salinity, or heavy metal toxicity, whereas LSU1 overexpression confers significant disease resistance in several of these conditions. Our data suggest that the network hub LSU1 plays an important role in co-ordinating plant immune responses across a spectrum of abiotic stress conditions.