The rice LATE ELONGATED HYPOCOTYL enhances salt tolerance by regulating Na+/K+ homeostasis and ABA signalling

The circadian clock plays multiple functions in the regulation of plant growth, development and response to various abiotic stress. Here, we showed that the core oscillator component late elongated hypocotyl (LHY) was involved in rice response to salt stress. The mutations of OsLHY gene led to reduced salt tolerance in rice. Transcriptomic analyses revealed that the OsLHY gene regulates the expression of genes related to ion homeostasis and the abscisic acid (ABA) signalling pathway, including genes encoded High-affinity K+ transporters (OsHKTs) and the stress-activated protein kinases (OsSAPKs). We demonstrated that OsLHY directly binds the promoters of OsHKT1;1, OsHKT1;4 and OsSAPK9 to regulate their expression. Moreover, the ossapk9 mutants exhibited salt tolerance under salt stress. Taken together, our findings revealed that OsLHY integrates ion homeostasis and the ABA pathway to regulate salt tolerance in rice, providing insights into our understanding of how the circadian clock controls rice response to salt stress.

Functionalized biochar from waste as a slow-release nutrient source: Application on tomato plants

Licorice processing waste was pyrolyzed at different temperatures (500 and 700 °C) to obtain biochar (BC500 and BC700) for use as a slow-release fertilizer on Solanum lycopersicum. The materials were characterized through BET analysis, SEM, elemental analysis, pHzc, and pyrolysis temperature effect was evaluated. The biochars were functionalized by the impregnation method to enrich them with nitrogen, phosphorus, and potassium (NPK), and desorption tests were performed in aqueous solution at different pHs (5 and 7). The pseudo-second-order model described well the release of all 3 macronutrients tested, BC500 was found to have slower release kinetics due to smaller pore size, reaching adsorption/desorption equilibrium after 14 days, compared with 10 for BC700, Kdes were lower in all 3 cases and NPK content was higher, initial pH did not change the release kinetics. BC500 was selected as an agricultural soil conditioner by testing at both different dosages of BC (0-25 %) and different NPK ratios (3:1:4 and 4:1:3). The treatment significance was evaluated. The best treatment resulted in BC dosage of 25 % nutrient ratio 4:1:3 which increased, compared to the control, total chlorophyll content (+38 %) and carotenoids (+15 %).

Integrative physiology and transcriptome reveal salt-tolerance differences between two licorice species: Ion transport, Casparian strip formation and flavonoids biosynthesis

BACKGROUND

Glycyrrhiza inflata Bat. and Glycyrrhiza uralensis Fisch. are both original plants of 'Gan Cao' in the Chinese Pharmacopoeia, and G. uralensis is currently the mainstream variety of licorice and has a long history of use in traditional Chinese medicine. Both of these species have shown some degree of tolerance to salinity, G. inflata exhibits higher salt tolerance than G. uralensis and can grow on saline meadow soils and crusty saline soils. However, the regulatory mechanism responsible for the differences in salt tolerance between different licorice species is unclear. Due to land area-related limitations, the excavation and cultivation of licorice varieties in saline-alkaline areas that both exhibit tolerance to salt and contain highly efficient active substances are needed. The systematic identification of the key genes and pathways associated with the differences in salt tolerance between these two licorice species will be beneficial for cultivating high-quality salt-tolerant licorice G. uralensis plant varieties and for the long-term development of the licorice industry. In this research, the differences in growth response indicators, ion accumulation, and transcription expression between the two licorice species were analyzed.

RESULTS

This research included a comprehensive comparison of growth response indicators, including biomass, malondialdehyde (MDA) levels, and total flavonoids content, between two distinct licorice species and an analysis of their ion content and transcriptome expression. In contrast to the result found for G. uralensis, the salt treatment of G. inflata ensured the stable accumulation of biomass and total flavonoids at 0.5 d, 15 d, and 30 d and the restriction of Na+ to the roots while allowing for more K+ and Ca2+ accumulation. Notably, despite the increase in the Na+ concentration in the roots, the MDA concentration remained low. Transcriptome analysis revealed that the regulatory effects of growth and ion transport on the two licorice species were strongly correlated with the following pathways and relevant DEGs: the TCA cycle, the pentose phosphate pathway, and the photosynthetic carbon fixation pathway involved in carbon metabolism; Casparian strip formation (lignin oxidation and translocation, suberin formation) in response to Na+; K+ and Ca2+ translocation, organic solute synthesis (arginine, polyamines, GABA) in response to osmotic stresses; and the biosynthesis of the nonenzymatic antioxidants carotenoids and flavonoids in response to antioxidant stress. Furthermore, the differential expression of the DEGs related to ABA signaling in hormone transduction and the regulation of transcription factors such as the HSF and GRAS families may be associated with the remarkable salt tolerance of G. inflata.

CONCLUSION

Compared with G. uralensis, G. inflata exhibits greater salt tolerance, which is primarily attributable to factors related to carbon metabolism, endodermal barrier formation and development, K+ and Ca2+ transport, biosynthesis of carotenoids and flavonoids, and regulation of signal transduction pathways and salt-responsive transcription factors. The formation of the Casparian strip, especially the transport and oxidation of lignin precursors, is likely the primary reason for the markedly higher amount of Na+ in the roots of G. inflata than in those of G. uralensis. The tendency of G. inflata to maintain low MDA levels in its roots under such conditions is closely related to the biosynthesis of flavonoids and carotenoids and the maintenance of the osmotic balance in roots by the absorption of more K+ and Ca2+ to meet growth needs. These findings may provide new insights for developing and cultivating G. uralensis plant species selected for cultivation in saline environments or soils managed through agronomic practices that involve the use of water with a high salt content.

A viral protein competitively bound to rice CIPK23 inhibits potassium absorption and facilitates virus systemic infection in rice

Potassium (K+) plays a crucial role as a macronutrient in the growth and development of plants. Studies have definitely determined the vital roles of K+ in response to pathogen invasion. Our previous investigations revealed that rice plants infected with rice grassy stunt virus (RGSV) displayed a reduction in K+ content, but the mechanism by which RGSV infection subverts K+ uptake remains unknown. In this study, we found that overexpression of RGSV P1, a specific viral protein encoded by viral RNA1, results in enhanced sensitivity to low K+ stress and exhibits a significantly lower rate of K+ influx compared to wild-type rice plants. Further investigation revealed that RGSV P1 interacts with OsCIPK23, an upstream regulator of Shaker K+ channel OsAKT1. Moreover, we found that the P1 protein recruits the OsCIPK23 to the Cajal bodies (CBs). In vivo assays demonstrated that the P1 protein competitively binds to OsCIPK23 with both OsCBL1 and OsAKT1. In the nucleus, the P1 protein enhances the binding of OsCIPK23 to OsCoilin, a homologue of the signature protein of CBs in Arabidopsis, and facilitates their trafficking through these CB structures. Genetic analysis indicates that mutant in oscipk23 suppresses RGSV systemic infection. Conversely, osakt1 mutants exhibited increased sensitivity to RGSV infection. These findings suggest that RGSV P1 hinders the absorption of K+ in rice plants by recruiting the OsCIPK23 to the CB structures. This process potentially promotes virus systemic infection but comes at the expense of inhibiting OsAKT1 activity.

Positive Regulatory Roles of Manihot esculenta HAK5 under K+ Deficiency or High Salt Stress

HAK/KUP/KT family members have been identified as playing key roles in K+ uptake and salt tolerance in numerous higher plants. However, their functions in cassava (Manihot esculenta Cantz) remain unknown. In this study, a gene encoding for a high-affinity potassium transporter (MeHAK5) was isolated from cassava and its function was investigated. Subcellular localization analysis showed that MeHAK5 is a plasma membrane-localized transporter. RT-PCR and RT-qPCR indicated that MeHAK5 is predominantly expressed in cassava roots, where it is upregulated by low potassium or high salt; in particular, its highest expression levels separately increased by 2.2 and 2.9 times after 50 µM KCl and 150 mM NaCl treatments. When heterologously expressed in yeast, MeHAK5 mediated K+ uptake within the cells of the yeast strain CY162 and rescued the salt-sensitive phenotype of AXT3K yeast. MeHAK5 overexpression in transgenic Arabidopsis plants exhibited improved growth and increased shoot K+ content under low potassium conditions. Under salt stress, MeHAK5 transgenic Arabidopsis plants accumulated more K+ in the shoots and roots and had reduced Na+ content in the shoots. As a result, MeHAK5 transgenic Arabidopsis demonstrated a more salt-tolerant phenotype. These results suggest that MeHAK5 functions as a high-affinity K+ transporter under K+ starvation conditions, improving K+/Na+ homeostasis and thereby functioning as a positive regulator of salt stress tolerance in transgenic Arabidopsis. Therefore, MeHAK5 may be a suitable candidate gene for improving K+ utilization efficiency and salt tolerance.

The EIN3/EIL-ERF9-HAK5 transcriptional cascade positively regulates high-affinity K+ uptake in Gossypium hirsutum

High-affinity K+ (HAK) transporters play essential roles in facilitating root K+ uptake in higher plants. Our previous studies revealed that GhHAK5a, a member of the HAK family, is crucial for K+ uptake in upland cotton. Nevertheless, the precise regulatory mechanism governing the expression of GhHAK5a remains unclear. The yeast one-hybrid screening was performed to identify the transcription factors responsible for regulating GhHAK5a, and ethylene response factor 9 (GhERF9) was identified as a potential candidate. Subsequent dual-luciferase and electrophoretic mobility shift assays confirmed that GhERF9 binds directly to the GhHAK5a promoter, thereby activating its expression. Silencing of GhERF9 decreased the expression of GhHAK5a and exacerbated K+ deficiency symptoms in leaves, also decreased K+ uptake rate and K+ content in roots. Additionally, it was observed that the application of ethephon (an ethylene-releasing reagent) resulted in a significant upregulation of GhERF9 and GhHAK5a, accompanied by an increased rate of K+ uptake. Expectedly, GhEIN3b and GhEIL3c, the two key components involved in ethylene signaling, bind directly to the GhERF9 promoter. These findings provide valuable insights into the molecular mechanisms underlying the expression of GhHAK5a and ethylene-mediated K+ uptake and suggest a potential strategy to genetically enhance cotton K+ uptake by exploiting the EIN3/EILs-ERF9-HAK5 module.

Chloride, glutathiones, and insect-derived elicitors introduced into the xylem trigger electrical signaling

Ricca assays allow the direct introduction of compounds extracted from plants or the organisms that attack them into the leaf vasculature. Using chromatographic fractionation of Arabidopsis (Arabidopsis thaliana) leaf extracts, we found glutamate was the most active low mass elicitor of membrane depolarization. However, other known elicitors of membrane depolarization are generated in the wound response. These include unstable aglycones generated by glucosinolate (GSL) breakdown. None of the aglycone-derived GSL-breakdown products, including nitriles and isothiocyanates, that we tested using Ricca assays triggered electrical activity. Instead, we found that glutathione and the GSL-derived compound sulforaphane glutathione triggered membrane depolarizations. These findings identify a potential link between GSL breakdown and glutathione in the generation of membrane depolarizing signals. Noting that the chromatographic fractionation of plant extracts can dilute or exchange ions, we found that Cl- caused glutamate receptor-like3.3-dependent membrane depolarizations. In summary, we show that, in addition to glutamate, glutathione derivatives as well as chloride ions will need to be considered as potential elicitors of wound-response membrane potential change. Finally, by introducing aphid (Brevicoryne brassicae) extracts or the flagellin-derived peptide flg22 into the leaf vasculature we extend the use of Ricca assays for the exploration of insect/plant and bacteria/plant interactions.

Occurrence, structure, and function of short cells in maize leaf epidermis

Short cells are specialised epidermal cells of grasses and they include cork and silica cells. The time of occurrence, distribution, and number of short cells differ among plants or tissues of the same plant. The present study aimed to assess the occurrence, structure, and function of short cells in the epidermis of maize (Zea mays L.) leaves from cultivar "Zhengdan 958″ under field and potted experimental conditions. Results showed that short cells occurred synchronously in multiple maize leaves. Few short cells occurred at the base of the fifth leaf; most were found at the middle and base of the sixth leaf, and throughout the seventh leaf. The accumulation of K+ and H2O2 in cork cells changed periodically with stomatal opening and closure, which was consistent with the accumulation of K+ and H2O2 in subsidiary cells; whereas no accumulation was observed in silica cells. Moreover, photosynthetic parameters and stomatal aperture were significantly higher in leaves containing short cells than in those without them in the same parts of different leaves or in different leaves at the same leaf position. Accumulation of K+ and H2O2 in cork cells increased with increasing water stress. In conclusion, short cells not only improved leaf mechanical support and photosynthetic performance, and maize drought resistance, but they also participated in stomatal regulation.

Accumulation, translocation, and fractionation of rare earth elements (REEs) in fern species of hyperaccumulators and non-hyperaccumulators growing in urban areas

The issue of ion-adsorption type rare earth deposits (IADs) in urban areas of South China has garnered significant attention due to its environmental implications. Hyperaccumulator-based phytoremediation is a potentially effective solution for reducing the environmental impact of IADs in urban areas, particularly using ferns as they are known to be REE hyperaccumulators. However, the ability of different fern species to accumulate REEs in urban areas remains unknown. In this study, four fern species, including known hyperaccumulators (Dicranopteris linearis and Blechnum orientale) and other ferns (Pteris ensiformis and Cibotium barometz), were studied to investigate their REE accumulation abilities in the Guangzhou urban area. The aboveground parts of Dicranopteris linearis (848.7 μg g-1) and Blechum orientale (1046.8 μg g-1) have been found to accumulate high concentrations of REEs, demonstrating they probably can be applied for phytoremediation in the natural environments. Despite having lower REE concentrations than REE hyperaccumulators, Pteris ensiformis and Cibotium barometz still probably have the function as phytostabilizers in urban areas, as REEs can be enriched in their roots beyond the normal levels of plants. The enrichment of REEs in ferns is influenced by the availability of various nutrients (K, Ca, Fe, and P), which probably can be associated with different growth processes. The four fern species show LREE enrichment, moderate Eu anomalies and different Ce anomalies. It is difficult to absorb and transfer Ce to the aboveground parts of Blechnum orientale and Cibotium barometz. The study also identified selective enrichment of Ce in Pteris ensiformis, which has potential for comprehensive extraction of REEs when combined with other REE hyperaccumulators. REE fractionations are probably determined by the specific characteristics of different fern parts. Overall, these findings provide insights for addressing potential environmental problems related to IADs and offer guidelines for phytoremediation technology in addressing high REE levels in urban areas.

The Molecular Mechanism of Potassium Absorption, Transport, and Utilization in Rice

Potassium is essential for plant growth and development and stress adaptation. The maintenance of potassium homeostasis involves a series of potassium channels and transporters, which promote the movement of potassium ions (K+) across cell membranes and exhibit complex expression patterns and regulatory mechanisms. Rice is a major food crop in China. The low utilization rate of potassium fertilizer limits the yield and quality of rice. Elucidating the molecular mechanisms of potassium absorption, transport, and utilization is critical in improving potassium utilization efficiency in rice. Although some K+ transporter genes have been identified from rice, research on the regulatory network is still in its infancy. Therefore, this review summarizes the relevant information on K+ channels and transporters in rice, covering the absorption of K+ in the roots, transport to the shoots, the regulation pathways, the relationship between K+ and the salt tolerance of rice, and the synergistic regulation of potassium, nitrogen, and phosphorus signals. The related research on rice potassium nutrition has been comprehensively reviewed, the existing research foundation and the bottleneck problems to be solved in this field have been clarified, and the follow-up key research directions have been pointed out to provide a theoretical framework for the cultivation of potassium-efficient rice.

Role of Bacteria-Derived Flavins in Plant Growth Promotion and Phytochemical Accumulation in Leafy Vegetables

Sinorhizobium meliloti 1021 bacteria secretes a considerable amount of flavins (FLs) and can form a nitrogen-fixing symbiosis with legumes. This strain is also associated with non-legume plants. However, its role in plant growth promotion (PGP) of non-legumes is not well understood. The present study evaluated the growth and development of lettuce (Lactuca sativa) and kale (Brassica oleracea var. acephala) plants inoculated with S. meliloti 1021 (FL+) and its mutant 1021ΔribBA, with a limited ability to secrete FLs (FL-). The results from this study indicated that inoculation with 1021 significantly (p < 0.05) increased the lengths and surface areas of the roots and hypocotyls of the seedlings compared to 1021ΔribBA. The kale and lettuce seedlings recorded 19% and 14% increases in total root length, respectively, following inoculation with 1021 compared to 1021ΔribBA. A greenhouse study showed that plant growth, photosynthetic rate, and yield were improved by 1021 inoculation. Moreover, chlorophylls a and b, and total carotenoids were more significantly (p < 0.05) increased in kale plants associated with 1021 than non-inoculated plants. In kale, total phenolics and flavonoids were significantly (p < 0.05) increased by 6% and 23%, respectively, and in lettuce, the increments were 102% and 57%, respectively, following 1021 inoculation. Overall, bacterial-derived FLs enhanced kale and lettuce plant growth, physiological indices, and yield. Future investigation will use proteomic approaches combined with plant physiological responses to better understand host-plant responses to bacteria-derived FLs.

The Sweet Potato K+ Transporter IbHAK11 Regulates K+ Deficiency and High Salinity Stress Tolerance by Maintaining Positive Ion Homeostasis

The K⁺ transporter KT/HAK/KUP (K⁺ transporter/high-affinity K⁺/K⁺ uptake) family has a critical effect on K⁺ uptake and translocation in plants under different environmental conditions. However, the functional analysis of KT/HAK/KUP members in sweet potatoes is still limited. The present work reported the physiological activity of a new gene, IbHAK11, in the KT/HAK/KUP family in sweet potatoes. IbHAK11 expression increased significantly in the low K⁺-tolerant line compared with the low K⁺-sensitive line following treatment with low K⁺ concentrations. IbHAK11 upregulation promoted root growth in Arabidopsis under low K⁺ conditions. Under high saline stress, transgenic lines had superior growth and photosynthetic characteristics compared with the wild-type (WT). As for IbHAK11-overexpressing plants, activation of both the non-enzymatic and enzymatic reactive oxygen species (ROS) scavenging systems was observed. Therefore, IbHAK11-overexpressing plants had lower malondialdehyde (MDA) and ROS levels (including H₂O₂ and O^2-) compared with WT under salt-induced stress. We also found that under both low K⁺ and high salinity conditions, overexpression of IbHAK11 enhanced K⁺ translocation from the root to the shoot and decreased Na⁺ absorption in Arabidopsis. Consequently, IbHAK11 positively regulated K⁺ deficiency and high salinity stresses by regulating K⁺ translocation and Na⁺ uptake, thus maintaining K⁺/Na⁺ homeostasis in plants.

The miR166d/TaCPK7-D Signaling Module Is a Critical Mediator of Wheat (Triticum aestivum L.) Tolerance to K+ Deficiency

It is well established that potassium (K⁺) is an essential nutrient for wheat (Triticum aestivum L.) growth and development. Several microRNAs (miRNAs), including miR166, are reportedly vital roles related to plant growth and stress responses. In this study, a K⁺ starvation-responsive miRNA (miR166d) was identified, which showed increased expression in the roots of wheat seedlings exposed to low-K⁺ stress. The overexpression of miR166d considerably increased the tolerance of transgenic Arabidopsis plants to K⁺ deprivation treatment. Furthermore, disrupting miR166d expression via virus-induced gene silencing (VIGS) adversely affected wheat adaptation to low-K⁺ stress. Additionally, miR166d directly targeted the calcium-dependent protein kinase 7-D gene (TaCPK7-D) in wheat. The TaCPK7-D gene expression was decreased in wheat seedling roots following K⁺ starvation treatment. Silencing TaCPK7-D in wheat increased K⁺ uptake under K⁺ starvation. Moreover, we observed that the miR166d/TaCPK7-D module could affect wheat tolerance to K⁺ starvation stress by regulating TaAKT1 and TaHAK1 expression. Taken together, our results indicate that miR166d is vital for K⁺ uptake and K⁺ starvation tolerance of wheat via regulation of TaCPK7-D.

Aspergillus aculeatus enhances nutrient uptake and forage quality in bermudagrass by increasing phosphorus and potassium availability

Introduction

Potassium and phosphorus are essential macronutrients for plant growth and development. However, most P and K exist in insoluble forms, which are difficult for plants to directly absorb and utilize, thereby resulting in growth retardation of plants under P or K deficiency stress. The Aspergillus aculeatus fungus has growth-promoting characteristics and the ability to dissolve P and K.

Methods

Here, to investigate the physiological effects of A. aculeatus on bermudagrass under P or K deficiency, A. aculeatus and bermudagrass were used as experimental materials.

Results and discussion

The results showed that A. aculeatus could promote tolerance to P or K deficiency stress in bermudagrass, decrease the rate of leaf death, and increase the contents of crude fat as well as crude protein. In addition, A. aculeatus significantly enhanced the chlorophyll a+b and carotenoid contents. Moreover, under P or K deficiency stress, bermudagrass inoculated with A. aculeatus showed higher N, P, and K contents than non-inoculated plants. Furthermore, exogenous A. aculeatus markedly decreased the H2O2 level and CAT and POD activities. Based on our results, A. aculeatus could effectively improve the forage quality of bermudagrass and alleviate the negative effects of P or K deficiency stress, thereby playing a positive economic role in the forage industry.

Transcription factor OsNAC016 negatively regulates phosphate-starvation response in rice

Phosphate (Pi), the main form of inorganic phosphorus that can be absorbed by plants, is one of the most limiting macro-nutrients in plants. However, the underlying molecular mechanism determining how plants sense external Pi levels and reprogram transcriptional and adaptive responses is incompletely understood. At present, few rice NAC members have been reported to be involved in the signaling pathways of Pi homeostasis in plants. Here, our research demonstrated that OsNAC016, a Pi-starvation responsive gene in rice, was regulated by PHOSPHATE STARVATION RESPONSE protein 1 (OsPHR1) and OsPHR4. Under Pi-starvation stress, the root growth of OsNAC016-overexpression lines was inhibited more severely, and overexpression plants had lower Pi content than wild type, while osnac016 mutant was hyposensitive to Pi starvation, indicating that OsNAC016 negatively modulates rice Pi-starvation response. Chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR) analysis and transient transactivation assays indicated that OsNAC016 could activate the SPX-domain-containing protein 2 (OsSPX2) gene through binding to its promoter. Further, we found that Pi starvation enhanced OsNAC016 binding to the OsSPX2 promoter, thus strongly promoting OsSPX2 expression. At the same time, Pi starvation induced OsNAC016 protein accumulation in plants. Moreover, similar to OsSPX2, OsNAC016 negatively regulates leaf inclination by repressing the cell elongation in lamina joint in rice under Pi-starvation stress. Together, our findings demonstrate that OsNAC016 negatively regulates rice phosphate-starvation response and leaf inclination by activating OsSPX2 expression under Pi-starvation conditions. These data provide a strategy to create smart crops with ideal shoot architecture and high phosphorus utilization efficiency.

Nitrate-responsive OsMADS27 promotes salt tolerance in rice

Salt stress is a major constraint on plant growth and yield. Nitrogen (N) fertilizers are known to alleviate salt stress. However, the underlying molecular mechanisms remain unclear. Here, we show that nitrate-dependent salt tolerance is mediated by OsMADS27 in rice. The expression of OsMADS27 is specifically induced by nitrate. The salt-inducible expression of OsMADS27 is also nitrate dependent. OsMADS27 knockout mutants are more sensitive to salt stress than the wild type, whereas OsMADS27 overexpression lines are more tolerant. Transcriptomic analyses revealed that OsMADS27 upregulates the expression of a number of known stress-responsive genes as well as those involved in ion homeostasis and antioxidation. We demonstrate that OsMADS27 directly binds to the promoters of OsHKT1.1 and OsSPL7 to regulate their expression. Notably, OsMADS27-mediated salt tolerance is nitrate dependent and positively correlated with nitrate concentration. Our results reveal the role of nitrate-responsive OsMADS27 and its downstream target genes in salt tolerance, providing a molecular mechanism for the enhancement of salt tolerance by nitrogen fertilizers in rice. OsMADS27 overexpression increased grain yield under salt stress in the presence of sufficient nitrate, suggesting that OsMADS27 is a promising candidate for the improvement of salt tolerance in rice.

Linking plant diversity-productivity relationships to plant functional traits of dominant species and changes in soil properties in 15-year-old experimental grasslands

Positive plant diversity-productivity relationships are known to be driven by complementary resource use via differences in plant functional traits. Moreover, soil properties related to nutrient availability were shown to change with plant diversity over time; however, it is not well-understood whether and how such plant diversity-dependent soil changes and associated changes in functional traits contribute to positive diversity-productivity relationships in the long run. To test this, we investigated plant communities of different species richness (1, 2, 6, and 9 species) in a 15-year-old grassland biodiversity experiment. We determined community biomass production and biodiversity effects (net biodiversity [NEs], complementarity [CEs], and selection effects [SEs]), as well as community means of plant functional traits and soil properties. First, we tested how these variables changed along the plant diversity gradient and were related to each other. Then, we tested for direct and indirect effects of plant and soil variables influencing community biomass production and biodiversity effects. Community biomass production, NEs, CEs, SEs, plant height, root length density (RLD), and all soil property variables changed with plant diversity and the presence of the dominant grass species Arrhenatherum elatius (increase except for soil pH, which decreased). Plant height and RLD for plant functional traits, and soil pH and organic carbon concentration for soil properties, were the variables with the strongest influence on biomass production and biodiversity effects. Our results suggest that plant species richness and the presence of the dominant species, A. elatius, cause soil organic carbon to increase and soil pH to decrease over time, which increases nutrient availability favoring species with tall growth and dense root systems, resulting in higher biomass production in species-rich communities. Here, we present an additional process that contributes to the strengthening positive diversity-productivity relationship, which may play a role alongside the widespread plant functional trait-based explanation.

Genome-wide identification of Mg2+ transporters and functional characteristics of DlMGT1 in Dimocarpus longan

Longan (Dimocarpus Longan) is one of the most important fruit crops in Southern China. Lack of available Mg in acidic soil conditions is a limitation to further increasing longan yield. Magnesium transporter (MGT/MRS2) mediates the uptake, transport, and redistribution of Mg2+ in higher plants. To understand the role of MGTs family members in longan Mg deficiency. We identified and analyzed the protein characteristics, phylogeny, expression changes, subcellular localization, and transcriptional regulation of DlMGTs members. The results showed that, twelve DlMGTs are localized in the cell membrane, chloroplast, and nucleus. The evolutionary differences in MGTs between herbaceous and woody species in different plants. The DlMGTs promoters contained many cis-acting elements and transcription factor binding sites related to the hormone, environmental, and stress response. Subcellular localization assays showed that DlMGT1 localizes in the cell membrane of Arabidopsis protoplasts. The candidate transcription factor DlGATA16, which may regulate the expression of DlMGT1, was localized in the nucleus of tobacco leaves. Dual luciferase analysis demonstrated that DlGATA16 is a potential factor regulating the transcriptional activity of DlMGT1. In this study, we identified and analyzed DlMGTs on a genome-wide scale and the subcellular localization and interaction of DlMGT1 and DlGATA16, which has important implications for further functional analysis studies of MGTs and the use of MGT for longan genetic improvement.

Nondestructive characterization of diseased Chinese chive leaves using X-ray intensity ratios with microbeam synchrotron radiation X-ray fluorescence spectrometry

The Chinese chive (Allium tuberosum) is a core crop grown in Kochi Prefecture, Japan. However, withering symptoms occur during greenhouse growing, which have a negative impact on crop management Chinese chive leaves with physiological disorders (PD) or necrotic streak disease (ND) present with withering as typical blight symptoms. Excess or deficiency of elements may cause such withering in Chinese chive leaves with PD. Therefore, visualizing the elemental distribution in plant bodies may help clarify the cause of this withering. In this study, using synchrotron radiation X-ray fluorescence (SR-XRF) imaging, we examined the elemental distribution conditions in healthy Chinese chive leaves without withering, those that withered due to PD, and those that withered due to ND. Segmentation analysis of inductively coupled plasma-optical emission spectroscopy (ICP-OES) was performed on the SR-XRF imaged Chinese chive leaves and the data from the two analytical methods were compared. SR-XRF imaging provided more detailed data on elemental distribution compared with segmentation analysis using ICP-OES. Based on the SR-XRF imaging results, the X-ray intensity ratios for Ca/K, Fe/Mn, and Zn/Cu were calculated. These findings support that the Ca/K, Fe/Mn, and Zn/Cu X-ray intensity ratios can be used in the early detection of withered leaves and to predict the factors causing withering.

Combined analysis of mRNA and miRNA reveals the banana potassium absorption regulatory network and validation of miRNA160a

Potassium (K) has an important effect on the growth and development of plants. Banana contains higher K content than many other fruits, and its plant requires more K nutrient in soil. However, the soil in the banana-producing areas in China is generally deficient in K. Therefore, understanding the mechanism of banana K absorption may assist in providing effective strategy to solve this problem. This study used two banana varieties with contrasting K tolerance, 'Guijiao No. 1' (low-K tolerant), and 'Brazilian banana' (low-K sensitive)to investigate K absorption mechanisms in response to low-K stress through miRNA and mRNA sequencing analysis. Under low-K condition, 'Guijiao No.1' showed higher plant height, dry weight, tissue K content and ATPase activity. Analysis of transcription factors showed that they were mainly in the types or classes of MYB, AP-EREBP, bHLH, etc. The sequencing results showed that 'Guijiao No. 1' had 776 differentially expressed genes (DEGs) and 27 differentially expressed miRNAs (DEMs), and 'Brazilian banana' had 71 DEGs and 14 DEMs between normal and low K treatments. RT-qPCR results showed that all miRNAs and mRNAs showed similar expression patterns with RNA-Seq and transcriptome. miRNA regulatory network was constructed by integrated analysis of miRNA-mRNA data. miR160a was screened out as a key miRNA, and preliminary functional validation was performed. Arabidopsis overexpressing miR160a showed reduced tolerance to low K, and inhibited phenotypic traits such as shorter root length, and reduced K accumulation. The overexpressed miR160a had a targeting relationship with ARF10 and ARF16 in Arabidopsis. These results indicate that miR160a may regulate K absorption in bananas through the auxin pathway. This study provides a theoretical basis for further study on the molecular mechanism of banana response to low potassium stress.

SES1 is vital for seedling establishment and post-germination growth under high-potassium stress conditions in Arabidopsis thaliana

Background

The potassium ion (K⁺) plays an important role in maintaining plant growth and development, while excess potassium in the soil can cause stress to plants. The understanding of the molecular mechanism of plant's response to high KCl stress is still limited.

Methods

At the seed stage, wild type (WT) and SENSITIVE TO SALT1 (SES1) mutants were exposed to different concentrations of potassium treatments. Tolerance was assayed as we compared their performances under stress using seedling establishment rate and root length. Na⁺content, K⁺content, and K⁺/Na⁺ ratio were determined using a flame atomic absorption spectrometer. In addition, the expressions of KCl-responding genes and ER stress-related genes were also detected and analyzed using qRT-PCR.

Results

SES1 mutants exhibited seedling establishment defects under high potassium concentration conditions and exogenous calcium partially restored the hypersensitivity phenotype of ses1 mutants. The expression of some K⁺ transporter/channel genes were higher in ses1-2, and the ratio of potassium to sodium (K⁺/Na⁺) in ses1-2 roots decreased after KCl treatment compared with WT. Further analysis showed that the ER stress marker genes were dramatically induced by high K⁺ treatment and much higher expression levels were detected in ses1-2, indicating ses1-2 suffers a more serious ER stress than WT, and ER stress may influence the seedling establishment of ses1-2 under high KCl conditions.

Conclusion

These results strongly indicate that SES1 is a potassium tolerance relevant molecule that may be related to maintaining the seedling K⁺/Na⁺ balance under high potassium conditions during seedling establishment and post-germination growth. Our results will provide a basis for further studies on the biological roles of SES1 in modulating potassium uptake, transport, and adaptation to stress conditions.

Silicon Supplementation Alleviates Adverse Effects of Ammonium on Ssamchoo Grown in Home Cultivation System

Ssamchoo is recently attracting attention as a household hydroponic vegetable in Korea. It has a refreshing texture and a rich content of vitamins and fiber. Ssamchoo with a wide leaf area is suitable for traditional ssam or vegetable wraps, as well as a vegetable for salads; thus, it can be used in a variety of dishes. However, Ssamchoo plants responds sensitively to the nutrient solution, and it is often difficult to secure sufficient leaf area and robust growth using a commercial nutrient solution for leafy vegetables. This study consisted of three experiments conducted to develop the nutrient solution for Ssamchoo grown in a newly developed home hydroponic cultivation system using light-emitting diodes as the sole source of light. In the first experiment, growth and development of Ssamchoo in a representative commercial nutrient solution, Peters Professional (20-20-20, The Scotts Co., Marysville, OH, USA), was compared with laboratory-prepared nutrient solutions, GNU1 and GNU2. As a result, the Ssamchoo grown in Peters Professional had a high NH₄⁺ content in the tissue, leaf yellowing, darkened root color, and suppressed root hair development. In addition, adverse effects of ammonium such as low fresh weight and shorter shoot length were observed. In the second experiment, Peters Professional was excluded, and the ratio of NO₃^- to NH₄⁺ in the GNU1 and GNU2 nutrient solutions was set to four levels each (100:0, 83.3:16.7, 66.7:33.3, and 50:50). As a result, the fresh weights of 83.3:16.7 and 66.7:33.3 were the greatest, and the leaf color was a healthy green. However, at 100:0 and 50:50 NO₃^-/NH₄⁺ ratios, the fresh weight was low, and leaf yellowing, tip burn, and leaf burn appeared. The nutrient solution with a 83.3:16.7 NO₃^-- to-NH₄⁺ ratio, which gave the greatest fresh weight in the second experiment, was chosen as the control, while the solution with a 50:50 NO₃^-/NH₄⁺ ratio with a lower nitrate content among the two unfavorable treatments was selected as a treatment group for the next experiment. In the third experiment, NH₄⁺ was partially replaced with urea to make four different ratios of NO₃^- to NH₄⁺ to urea (83:17:0, 50:50:0, 50:25:25, and 50:0:50) in combination with two levels of Si (0 and 10.7 mmol·L^-1 Si). The greatest fresh weight was obtained in the treatment in which the NO₃^-/NH₄⁺/urea ratio was 50:25:25. In particular, when Si was added to the solution, there was no decrease in the number of leaves, and plants with the greatest fresh weight, chlorophyll content, and leaf area were obtained. The number of leaves and leaf area are important indicators of high productivity since the Ssamchoo is used in ssam dishes. It can be concluded that a solution with a NO₃^-/NH₄⁺/urea ratio of 50:25:25 and supplemented with 10.7 mmol·L^-1 Si is the most suitable nutrient solution for growing Ssamchoo in the home hydroponic system developed.

Phytomelatonin and plant mineral nutrition

Plant mineral nutrition is critical for agricultural productivity and for human nutrition; however, the availability of mineral elements is spatially and temporally heterogeneous in many ecosystems and agricultural landscapes. Nutrient imbalances trigger intricate signalling networks that modulate plant acclimation responses. One signalling agent of particular importance in such networks is phytomelatonin, a pleiotropic molecule with multiple functions. Evidence indicates that deficiencies or excesses of nutrients generally increase phytomelatonin levels in certain tissues, and it is increasingly thought to participate in the regulation of plant mineral nutrition. Alterations in endogenous phytomelatonin levels can protect plants from oxidative stress, influence root architecture, and influence nutrient uptake and efficiency of use through transcriptional and post-transcriptional regulation; such changes optimize mineral nutrient acquisition and ion homeostasis inside plant cells and thereby help to promote growth. This review summarizes current knowledge on the regulation of plant mineral nutrition by melatonin and highlights how endogenous phytomelatonin alters plant responses to specific mineral elements. In addition, we comprehensively discuss how melatonin influences uptake and transport under conditions of nutrient shortage.

Receptor-like protein kinase BAK1 promotes K+ uptake by regulating H+-ATPase AHA2 under low potassium stress

Potassium (K+) is one of the essential macronutrients for plant growth and development. However, the available K+ concentration in soil is relatively low. Plant roots can perceive low K+ (LK) stress, then enhance high-affinity K+ uptake by activating H+-ATPases in root cells, but the mechanisms are still unclear. Here, we identified the receptor-like protein kinase Brassinosteroid Insensitive 1-Associated Receptor Kinase 1 (BAK1) that is involved in LK response by regulating the Arabidopsis (Arabidopsis thaliana) plasma membrane H+-ATPase isoform 2 (AHA2). The bak1 mutant showed leaf chlorosis phenotype and reduced K+ content under LK conditions, which was due to the decline of K+ uptake capacity. BAK1 could directly interact with the AHA2 C terminus and phosphorylate T858 and T881, by which the H+ pump activity of AHA2 was enhanced. The bak1 aha2 double mutant also displayed a leaf chlorosis phenotype that was similar to their single mutants. The constitutively activated form AHA2Δ98 and phosphorylation-mimic form AHA2T858D or AHA2T881D could complement the LK sensitive phenotypes of both aha2 and bak1 mutants. Together, our data demonstrate that BAK1 phosphorylates AHA2 and enhances its activity, which subsequently promotes K+ uptake under LK conditions.

Transporter NRT1.5/NPF7.3 suppresses primary root growth under low K+ stress by regulating the degradation of PIN-FORMED2

BACKGROUND

The availability of potassium is one of the main environmental factors for modifying the plasticity of root architecture. Many potassium channels and transporters are involved in regulating primary root growth in response to low potassium stress. NRT1.5/NPF7.3 transporter is a NO₃^-/H⁺ and K⁺/H⁺ cotransporter, and participates in NO₃^- and K⁺ translocation from the roots to the shoots. However, the underlying mechanism of NRT1.5-regulated primary root growth under low potassium stress is unclear.

RESULTS

We show that NRT1.5/NPF7.3 inhibited primary root growth under low potassium conditions by regulating the accumulation of PIN2 protein and auxin levels. Under low potassium conditions, the mutants nrt1.5 and lks2 exhibited longer primary roots, longer meristem regions and elongation zones of primary roots, and more cell activity in the meristem region compared to WT plants, revealing the involvement of NRT1.5 in LK (low potassium)-inhibition primary root growth. In addition, exogenous auxin (IAA), auxin analogue (NAA, 2.4-D) or auxin precursor (IBA) promoted the primary root growth of WT and the complementation line NRT1.5 COM plants. In addition, the application of NPA inhibited the primary root growth of the nrt1.5 and lks2 mutants. Auxin accumulation was higher in the root tip of nrt1.5 plants than in WT plants, indicating that NRT1.5 regulates root growth inhibition by regulating auxin distribution. Furthermore, PIN2 was degraded more quickly in nrt1.5 plants under LK stress.

CONCLUSIONS

Our findings reveal that NRT1.5 inhibits primary root growth by modulating the auxin level in the root tip via the degradation of PIN2.

The role of nutritional impairment in carbon-water balance of silver fir drought-induced dieback

Rear-edge populations at the xeric distribution limit of tree species are particularly vulnerable to forest dieback triggered by drought. This is the case of silver fir (Abies alba) forests located in Southwestern Europe. While silver fir drought-induced dieback patterns have been previously explored, information on the role played by nutritional impairment is lacking despite its potential interactions with tree carbon-water balances. We performed a comparative analysis of radial growth, intrinsic water-use efficiency (iWUE), oxygen isotopes (δ¹⁸ O) and nutrient concentrations in leaves of declining (DD) and non-declining (ND) trees in silver fir in four forests in the Spanish Pyrenees. We also evaluated the relationships among dieback predisposition, intraspecific trait variation (wood density and leaf traits) and rhizosphere soil physical-chemical properties. The onset of growth decline in DD trees occurred more than two decades ago, and they subsequently showed low growth resilience against droughts. The DD trees presented consistently lower foliar concentrations of nutrients such as P, K, Cu and Ni than ND trees. The strong effects of foliar nutrient status on growth resilience indices support the key role played by mineral nutrition in tree functioning and growth before, during and after drought. In contrast, variability in wood density and leaf morphological traits, as well as soil properties, showed weak relationships with tree nutritional status and drought performance. At the low elevation, warmer sites, DD trees showed stronger climate-growth relationships and lower δ¹⁸ O than ND trees. The uncoupling between iWUE and δ¹⁸ O, together with the positive correlations between P and K leaf concentrations and δ¹⁸ O, point to deeper soil/bedrock water sources and vertical decoupling between nutrient and water uptake in DD trees. This study provides novel insights into the mechanisms driving silver fir dieback and highlights the need to incorporate tree nutrition into forest dieback studies.

The Sweetpotato Voltage-Gated K+ Channel β Subunit, KIbB1, Positively Regulates Low-K+ and High-Salinity Tolerance by Maintaining Ion Homeostasis

Voltage-gated K⁺ channel β subunits act as a structural component of K_in channels in different species. The β subunits are not essential to the channel activity but confer different properties through binding the T1 domain or the C-terminal of α subunits. Here, we studied the physiological function of a novel gene, KIbB1, encoding a voltage-gated K⁺ channel β subunit in sweetpotato. The transcriptional level of this gene was significantly higher in the low-K⁺-tolerant line than that in the low-K⁺-sensitive line under K⁺ deficiency conditions. In Arabidopsis, KIbB1 positively regulated low-K⁺ tolerance through regulating K⁺ uptake and translocation. Under high-salinity stress, the growth conditions of transgenic lines were obviously better than wild typr (WT). Enzymatic and non-enzymatic reactive oxygen species (ROS) scavenging were activated in transgenic plants. Accordingly, the malondialdehyde (MDA) content and the accumulation of ROS such as H₂O₂ and O²⁻ were lower in transgenic lines under salt stress. It was also found that the overexpression of KIbB1 enhanced K⁺ uptake, but the translocation from root to shoot was not affected under salt stress. This demonstrates that KIbB1 acted as a positive regulator in high-salinity stress resistance through regulating Na⁺ and K⁺ uptake to maintain K⁺/Na⁺ homeostasis. These results collectively suggest that the mechanisms of KIbB1 in regulating K⁺ were somewhat different between low-K⁺ and high-salinity conditions.

Phosphorus Acquisition and Utilization in Plants

Tremendous progress has been made on molecular aspects of plant phosphorus (P) nutrition, often without heeding information provided by soil scientists, ecophysiologists, and crop physiologists. This review suggests ways to integrate information from different disciplines. When soil P availability is very low, P-mobilizing strategies are more effective than mycorrhizal strategies. Soil parameters largely determine how much P roots can acquire from P-impoverished soil, and kinetic properties of P transporters are less important. Changes in the expression of P transporters avoid P toxicity. Plants vary widely in photosynthetic P-use efficiency, photosynthesis per unit leaf P. The challenge is to discover what the trade-offs are of different patterns of investment in P fractions. Less investment may save P, but are costs incurred? Are these costs acceptable for crops? These questions can be resolved only by the concerted action of scientists working at both molecular and physiological levels, rather than pursuing these problems independently.

The potassium channel GhAKT2bD is regulated by CBL-CIPK calcium signaling complexes and facilitates K+ allocation in cotton

Efficient allocation of the essential nutrient potassium (K⁺ ) is a central determinant of plant ion homeostasis and involves AKT2 K⁺ channels. Here, we characterize four AKT2 K⁺ channels from cotton and report that xylem and phloem expressed GhAKT2bD facilitates K⁺ allocation and that AKT2-silencing impairs plant growth and development. We uncover kinase activity-dependent activation of GhAKT2bD-mediated K⁺ uptake by AtCBL4-GhCIPK1 calcium signaling complexes in HEK293T cells. Moreover, AtCBL4-AtCIPK6 complexes known to convey activation of AtAKT2 in Arabidopsis also activate cotton GhAKT2bD in HEK293T cells. Collectively, these findings reveal an essential role for AKT2 in the source-sink allocation of K⁺ in cotton and identify GhAKT2bD as subject to complex regulation by CBL-CIPK Ca²⁺ sensor-kinase complexes.

Soil type and fertilizer rate affect wheat (Triticum aestivum L.) yield, quality and nutrient use efficiency in Ayiba, northern Ethiopia

The blanket NP fertilizer recommendation over the past five decades in Ethiopia did not result in a significant increment of crop productivity. The main lack of success was highly linked to the extrapolating approach of one site success to others without considering the climate, soil, and ecological setting and variations. As a result, a new fertilization approach was desperately needed, and with this premise, new blended fertilizers are now being introduced to replace the conventional approach. Thus, the objective of this study was to examine the effect of NPSZnB blended fertilizer on bread wheat yield attributes, quality traits and use efficiency in two different soil types under rain-fed conditions in Ayiba, northern Ethiopia. Relevant agronomic data were evaluated and recorded from plots of each soil types for analysis. The analysis of variance revealed a significant (p < 0.001) variation on all the agronomic and grain quality traits due to the main and interaction effects of soil type and fertilizer treatment factors. Most agronomic and quality characteristics recorded the highest result in the highest treatment applications (175 and 150 kg NPSZnB ha^-1) in both soils. Yield and grain quality traits of bread wheat was also found better under fertilized plots than unfertilized plots. In both soil types increasing application of the new blended fertilizer rate from 50-175 kg NPSZnB ha^-1 showed an increasing trend in grain yield from 1.6 to 4.3 and 2.5 to 5.4 t ha^-1 in Vertisol and Cambisol soils, respectively. The varied yield as a response of fertilizer treatments across soils signifies soil-specific fertilization approach is critically important for production increment. On the other hand, based on the partial budget analysis the highest net benefit with the highest marginal rate of return in both Vertisol and Cambisol soils were obtained when treated with 100 and 125 kg NPSZnB ha^-1, respectively. Therefore, to produce optimum bread wheat yield under rainfed conditions in Ayiba (northern Ethiopia) fertilizing Vertisols with 100 kg NPSZnB ha^-1 and fertilizing Cambisols with 125 kg NPSZnB ha^-1 is recommended.

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.

Transcriptome-wide identification and expression analysis of the KT/HAK/KUP family in Salicornia europaea L. under varied NaCl and KCl treatments

Background

The KT/HAK/KUP (KUP) transporters play important roles in potassium (K⁺) uptake and translocation, regulation of osmotic potential, salt tolerance, root morphogenesis and plant development. However, the KUP family has not been systematically studied in the typical halophyte Salicornia europaea L., and the specific expression patterns of SeKUPs under NaCl condition and K⁺ deficiency are unknown.

Methods

In this study, SeKUPs were screened from PacBio transcriptome data of Salicornia europaea L. using bioinformatics. The identification, phylogenetic analysis and prediction of conserved motifs of SeKUPs were extensively explored. Moreover, the expression levels of 24 selected SeKUPs were assayed by real-time quantitative polymerase chain reaction (RT-qPCR).

Results

In this study, a total of 24 putative SeKUPs were identified in S. europaea. Nineteen SeKUPs with the fixed domain EA[ML]FADL were used to construct the phylogenetic tree, and they were divided into four clusters (clusters I-IV). MEME analysis identified 10 motifs in S. europaea, and the motif analysis suggested that 19 of the identified SeKUPs had at least four K⁺ transporter motifs existed in all SeKUPs (with the exception of SeKUP-2). The RT-qPCR analysis showed that the expression levels of most SeKUPs were significantly up-regulated in S. europaea when they were exposed to K⁺ deficiency and high salinity, implying that these SeKUPs may play a key role in the absorption and transport of K⁺ and Na⁺ in S. europaea.

Discussions

Our results laid the foundation for revealing the salt tolerance mechanism of SeKUPs, and provided key candidate genes for further studies on the function of KUP family in S. europaea.

Comparisons of Anatomical Characteristics and Transcriptomic Differences between Heterografts and Homografts in Pyrus L

Pear (Pyrus L.) is an important temperate fruit worldwide, and grafting is widely used in pear vegetative propagation. However, the mechanisms of graft healing or incompatibility remain poorly understood in Pyrus. To study the differences in graft healing in Pyrus, the homograft "Qingzhen D1/Qingzhen D1" and the heterograft "QAUP-1/Qingzhen D1" as compatibility and incompatibility combinations were compared. Anatomical differences indicated the healing process was faster in homografts than in heterografts. During the healing process, four critical stages in graft union formation were identified in the two types of grafts. The expression of the genes associated with hormone signaling (auxin and cytokinins), and lignin biosynthesis was delayed in the healing process of heterografts. In addition, the PbBglu13 gene, encoded β-glucosidase, was more highly up-regulated in heterografts than in homografts to promote healing. Meanwhile, the most of DEGs related starch and sucrose metabolism were found to be up-regulated in heterografts; those results indicated that cellulose and sugar signals were also involved in graft healing. The results of this study improved the understanding of the differences in the mechanisms of graft healing between homografts and heterografts.

Integrated Analysis of miRNAs Associated With Sugarcane Responses to Low-Potassium Stress

Sugarcane is among the most important global crops and a key bioenergy source. Sugarcane production is restricted by limited levels of available soil potassium (K⁺). The ability of plants to respond to stressors can be regulated by a range of microRNAs (miRNAs). However, there have been few studies regarding the roles of miRNAs in the regulation of sugarcane responses to K⁺-deficiency. To understand how these non-coding RNAs may influence sugarcane responses to low-K⁺ stress, we conducted expression profiling of miRNAs in sugarcane roots under low-K⁺ conditions via high-throughput sequencing. This approach led to the identification of 324 and 42 known and novel miRNAs, respectively, of which 36 were found to be differentially expressed miRNAs (DEMs) under low-K⁺ conditions. These results also suggested that miR156-x/z and miR171-x are involved in these responses as potential regulators of lateral root formation and the ethylene signaling pathway, respectively. A total of 705 putative targets of these DEMs were further identified through bioinformatics predictions and degradome analyses, and GO and KEGG enrichment analyses revealed these target mRNAs to be enriched for catalytic activity, binding functions, metabolic processes, plant hormone signal transduction, and mitogen-activated protein kinase (MAPK) signaling. In summary, these data provide an overview of the roles of miRNAs in the regulation of sugarcane response to low-K⁺ conditions.

STOP1 Regulates LKS1 Transcription and Coordinates K+/NH4+ Balance in Arabidopsis Response to Low-K+ Stress

Potassium and nitrogen are essential mineral elements for plant growth and development. The protein kinase LKS1/CIPK23 is involved in both K⁺ and NH₄⁺ uptake in Arabidopsis root. The transcripts of LKS1 can be induced by low K⁺ (0.1 mM) and high NH₄⁺ (30 mM); however, the molecular mechanism is still unknown. In this study, we isolated the transcription factor STOP1 that positively regulates LKS1 transcription in Arabidopsis responses to both low-K⁺ and high-NH₄⁺ stresses. STOP1 proteins can directly bind to the LKS1 promoter, promoting its transcription. The stop1 mutants displayed a leaf chlorosis phenotype similar to lks1 mutant when grown on low-K⁺ and high-NH₄⁺ medium. On the other hand, STOP1 overexpressing plants exhibited a similar tolerant phenotype to LKS1 overexpressing plants. The transcript level of STOP1 was only upregulated by low K⁺ rather than high NH₄⁺; however, the accumulation of STOP1 protein in the nucleus was required for the upregulation of LKS1 transcripts in both low-K⁺ and high-NH₄⁺ responses. Our data demonstrate that STOP1 positively regulates LKS1 transcription under low-K⁺ and high-NH₄⁺ conditions; therefore, LKS1 promotes K⁺ uptake and inhibits NH₄⁺ uptake. The STOP1/LKS1 pathway plays crucial roles in K⁺ and NH₄⁺ homeostasis, which coordinates potassium and nitrogen balance in plants in response to external fluctuating nutrient levels.

Comparing the Effects of N and P Deficiency on Physiology and Growth for Fast- and Slow-Growing Provenances of Fraxinus mandshurica

With the continuous increase in atmospheric carbon dioxide emissions, nitrogen (N) and phosphorus (P) as mineral elements increasingly restrict plant growth. To explore the effect of deficiency of P and N on growth and physiology, Fraxinus mandshurica (hereafter “F. mandshurica”) Rupr. annual seedlings of Wuchang (WC) provenance with fast growth and Dailing (DL) provenance with slow growth were treated with complete nutrition or starvation of N (N-), P (P-) or both elements (NP-). Although P- and N- increased the use efficiency of P (PUE) and N (NUE), respectively, they reduced the leaf area, chlorophyll content and activities of N assimilation enzymes (NR, GS, GOGAT), which decreased the dry weight and P or N amount. The free amino acid content and activities of Phosphoenolpyruvate carboxylase (PEPC) and acid phosphatase enzymes were reduced by N-. The transcript levels of NRT2.1, NRT2.4, NRT2.5, NRT2.7, AVT1, AAP3, NIA2, PHT1-3, PHT1-4 and PHT2-1 in roots were increased, but those of NRT2.1, NRT2.4, NRT2.5, PHT1-3, PHT1-4, PHT2-1 and AAP3 in leaves were reduced by P-. WC was significantly greater than DL under P- in dry weight, C amount, N amount, leaf area, PUE, NUE, which related to greater chlorophyll content, PEPC enzyme activity, N assimilation enzyme activities, and transcript levels of N and P transporter genes in roots and foliage, indicating a greater ability of WC to absorb, transport and utilize N and P under P-. WC was also greater than DL under N- in terms of the above indicators except the transcript levels of N and P assimilation genes, but most of the indicators did not reach a significant level, indicating that WC might be more tolerant to N- than DL, which requires further verification. In summary, WC was identified as a P-efficient provenance, as the growth rate was greater for the genetic type with high than low tolerance to P-.

Association between plant nutrients, the development of Huanglongbing and abnormal growth symptoms in navel orange

Huanglongbing (HLB) causes extensive damage in citrus orchards worldwide. Symptoms include blotchy mottle leaf (BML) and little leaf chlorosis (LLC), and nutrient deficiency usually occurs concurrently. However, the relationship between plant mineral content and infection with Candidatus Liberibacter asiaticus (CLas) is not clearly established. We sampled 7-month-old autumn shoots with three characteristic phenotypes, asymptomatic leaf (AL), BML and LLC, representing HLB disease progression, and further divided samples into CLas-infected and uninfected based on PCR analysis. HLB infection decreased transfer coefficients of Mg and K from leaf to phloem tissues through regulation of the transporter genes Cs3g03790.1 and PtrMGT5, increasing the content of leaf Mg and K. HLB infection also decreased leaf Zn, xylem Ca and phloem Ca and Zn content. Leaf Ca, Mg, Zn and B content decreased while leaf K content increased significantly as symptoms progressed from AL to LLC. The transport of P from leaf to phloem tissue, as evaluated by the transfer coefficient, was regulated by the transporter CsiPT2, resulting in irregular levels of leaf P. Our results provide insights into the nutrient dynamics in Citrus in response to CLas infection and the progression of HLB symptoms.

Genome-Wide Identification, Genomic Organization, and Characterization of Potassium Transport-Related Genes in Cajanus cajan and Their Role in Abiotic Stress

Potassium is the most important and abundant inorganic cation in plants and it can comprise up to 10% of a plant's dry weight. Plants possess complex systems of transporters and channels for the transport of K+ from soil to numerous parts of plants. Cajanus cajan is cultivated in different regions of the world as an economical source of carbohydrates, fiber, proteins, and fodder for animals. In the current study, 39 K+ transport genes were identified in C. cajan, including 25 K+ transporters (17 carrier-like K+ transporters (KUP/HAK/KTs), 2 high-affinity potassium transporters (HKTs), and 6 K+ efflux transporters (KEAs) and 14 K+ channels (9 shakers and 5 tandem-pore K+ channels (TPKs). Chromosomal mapping indicated that these genes were randomly distributed among 10 chromosomes. A comparative phylogenetic analysis including protein sequences from Glycine max, Arabidopsis thaliana, Oryza sativa, Medicago truncatula Cicer arietinum, and C. cajan suggested vital conservation of K+ transport genes. Gene structure analysis showed that the intron/exon organization of K+ transporter and channel genes is highly conserved in a family-specific manner. In the promoter region, many cis-regulatory elements were identified related to abiotic stress, suggesting their role in abiotic stress response. Abiotic stresses (salt, heat, and drought) adversely affect chlorophyll, carotenoids contents, and total soluble proteins. Furthermore, the activities of catalase, superoxide, and peroxidase were altered in C. cajan leaves under applied stresses. Expression analysis (RNA-seq data and quantitative real-time PCR) revealed that several K+ transport genes were expressed in abiotic stress-responsive manners. The present study provides an in-depth understanding of K+ transport system genes in C. cajan and serves as a basis for further characterization of these genes.

MYB77 regulates high-affinity potassium uptake by promoting expression of HAK5

In Arabidopsis, the high-affinity K⁺ transporter HAK5 is the major pathway for root K⁺ uptake when below 100 µM; HAK5 responds to Low-K⁺ (LK) stress by strongly and rapidly increasing its expression during K⁺ -deficiency. Therefore, positive regulators of HAK5 expression have the potential to improve K⁺ uptake under LK. Here, we show that mutants of the transcription factor MYB77 share a LK-induced leaf chlorosis phenotype, lower K⁺ content, and lower Rb⁺ uptake of the hak5 mutant, but not the shorter root growth, and that overexpression of MYB77 enhanced K⁺ uptake and improved tolerance to LK stress. Furthermore, we demonstrated that MYB77 positively regulates the expression of HAK5, by binding to the HAK5 promoter and enhances high-affinity K⁺ uptake of roots. As such, our results reveal a novel pathway for enhancing HAK5 expression under LK stress, and provides a candidate for increasing the tolerance of plants to LK.

Gibberellin biosynthesis inhibitor mepiquat chloride enhances root K+ uptake in cotton by modulating plasma membrane H+-ATPase

Potassium deficiency causes severe losses in yield and quality in crops. Mepiquat chloride, a plant growth regulator, can increase K+ uptake in cotton (Gossypium hirsutum), but the underlying physiological mechanisms remain unclear. In this study, we used a non-invasive micro-test technique to measure K+ and H+ fluxes in the root apex with or without inhibitors of K+ channels, K+ transporters, non-selective cation channels, and plasma membrane H+-ATPases. We found that soaking seeds in mepiquat chloride solution increased the K+ influx mediated by K+ channels and reduced the K+ efflux mediated by non-selective cation channels in cotton seedlings. Mepiquat chloride also increased negative membrane potential (Em) and the activity of plasma membrane H+-ATPases in roots, due to higher levels of gene expression and protein accumulation of plasma membrane H+-ATPases as well as phosphorylation of H+-ATPase 11 (GhAHA11). Thus, plasma membrane hyperpolarization mediated by H+-ATPases was able to stimulate the activity of K+ channels in roots treated with mepiquat chloride. In addition, reduced K+ efflux under mepiquat chloride treatment was associated with reduced accumulation of H2O2 in roots. Our results provide important insights into the mechanisms of mepiquat chloride-induced K+ uptake in cotton and hence have the potential to help in improving K nutrition for enhancing cotton production.

The Highs and Lows of P Supply in Medical Cannabis: Effects on Cannabinoids, the Ionome, and Morpho-Physiology

Environmental conditions, including the availability of mineral nutrients, affect secondary metabolism in plants. Therefore, growing conditions have significant pharmaceutical and economic importance for Cannabis sativa. Phosphorous is an essential macronutrient that affects central biosynthesis pathways. In this study, we evaluated the hypothesis that P uptake, distribution and availability in the plant affect the biosynthesis of cannabinoids. Two genotypes of medical "drug-type" cannabis plants were grown under five P concentrations of 5, 15, 30, 60, and 90 mg L-1 (ppm) in controlled environmental conditions. The results reveal several dose-dependent effects of P nutrition on the cannabinoid profile of both genotypes, as well as on the ionome and plant functional physiology, thus supporting the hypothesis: (i) P concentrations ≤15 mg L-1 were insufficient to support optimal plant function and reduced photosynthesis, transpiration, stomatal conductance and growth; (ii) 30-90 mg L-1 P was within the optimal range for plant development and function, and 30 mg L-1 P was sufficient for producing 80% of the maximum yield; (iii) Ionome: about 80% of the plant P accumulated in the unfertilized inflorescences; (iv) Cannabinoids: P supply higher than 5 mg L-1 reduced Δ9-tetrahydrocannabinolic acid (THCA) and cannabidiolic acid (CBDA) concentrations in the inflorescences by up to 25%. Cannabinoid concentrations decreased linearly with increasing yield, consistent with a yield dilution effect, but the total cannabinoid content per plant increased with increasing P supply. These results reveal contrasting trends for effects of P supply on cannabinoid concentrations that were highest under <30 mg L-1 P, vs. inflorescence biomass that was highest under 30-90 mg L-1 P. Thus, the P regime should be adjusted to reflect production goals. The results demonstrate the potential of mineral nutrition to regulate cannabinoid metabolism and optimize pharmacological quality.

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.

Effect of Micronutrient and Hormone on Microalgae Growth Assessment for Biofuel Feedstock

The individual and combined effects of micronutrients and hormones on freshwater-borne microalgae growth were investigated for biofuel feedstock in this experimental study. Five algal strains of Chlorella sp., Chlorococcum sp., Phormidium sp., Chlorella sp. and Cosmarium sp., AZH, AZS, ZAA1, ZAA2, and ZAA3, respectively, have been investigated. These strains were treated using different concentrations of micronutrients (iron chloride, manganese chloride, and sodium molybdenum oxide) and hormone (salicylic acid). The different treatments’ growth effects were as follows: iron chloride > sodium molybdenum oxide ˃ manganese chloride > salicylic acid. The order of the increases in the number of microalgal strain cells achieved by the application of the micronutrients and hormone was AZH > AZS > ZAA3 > ZAA2 > ZAA1. The combined treatments produced higher growth rates than the individual treatments, with the order of their effects being micronutrients + hormone > all three micronutrients > hormone alone. The increase in the number of microalgal strain cells under combined treatment was ZAA3 > AZH > AZS > ZAA2 and assessed using one-way ANOVA.