Progress and Applications of Plant Growth-Promoting Bacteria in Salt Tolerance of Crops

Transcriptome analysis reveals the mechanism of mixed oligosaccharides in the response of rice seedlings to abiotic stresses

Salinity and alkalinity stresses severely suppress rice seedling growth and substantially reduce rice yield; whereas the application of oligosaccharides as plant growth regulators has been demonstrated to remarkably enhance crop tolerance to abiotic stresses. To investigate the potential growth-promoting effects of KP-priming (mixed-oligosaccharides, 1.12 mg mL-1) on rice seedlings under salinity (100 mmol L-1 NaCl) and alkalinity (10 mmol L-1 Na2CO3) stresses, plant morphology and physiology assessments, and transcriptome analyses were performed. The KP-priming significantly improved rice seedling tolerance to salinity and alkalinity stresses, evidenced by increases in plant height, dry matter weight, and fresh weight, and improved root morphology (root length, surface area) and vitality by 10.27-89.06%. Leaf cell membrane stability was improved in KP-priming by increasing the soluble sugar content and superoxide dismutase, peroxidase, and catalase activities by 2.74-97.32%, and reducing accumulation of malondialdehyde and hydrogen peroxide by 17.67-49.70%. KP-priming treatment significantly enhanced leaf photosynthetic capacity through promoting photosynthetic pigments and maximum photochemical efficiency by 2.34-135.76%, and enhancing leaf stomatal aperture by 21.58-75.84%. Transcriptomic analysis revealed that differentially expressed genes in response to KP-priming under salt and alkaline stresses were predominantly associated with photosynthetic pathways. Total 4125 (salinity) and 1971 (alkalinity) DEGs were identified under stresses compared to KP-priming. Transcriptional profiling of KP-priming-treated leaves demonstrated significant up-regulation of key photosynthetic genes, including OsRBCS5, PGR5, Se5, OsPORA, GRA78, OsLhcb7, and OsPS1-F. This coordinated gene expression was functionally associated with enhanced leaf photosynthesis capacity and mitigated oxidative damage through improved electron transport and reactive oxygen species scavenging mechanisms. Our findings demonstrated that KP-priming initiated a self-regulatory mechanism in plants, orchestrating a dual protective response that simultaneously mitigated oxidative damage while enhancing photosynthetic efficiency and stress resilience. This study provided initial insights into using KP-priming to alleviate salinity and alkalinity stresses and its underlying molecular mechanisms, which is valuable for both field management practices and understanding rice tolerance to abiotic stresses.

Characterizing Wheat Rhizosphere Bacterial Microbiome Dynamics Under Salinity Stress: Insights from 16S rRNA Metagenomics for Enhancing Stress Tolerance

Salinity is one of the most important abiotic stress factors affecting wheat production. Salt in the soil is a major environmental stressor that can affect the bacterial community in the rhizosphere of wheat. The bacteria in the plant's rhizosphere promote growth and stress tolerance, which vary by variety and location. Nevertheless, the soil harbors some of the most diverse microbial communities, while the rhizosphere selectively recruits according to the needs of plants in a complex harmonic regulation. The microbial composition and diversity under normal and saline conditions were assessed by comparing the rhizosphere of wheat with soil using 16S rRNA gene amplicon sequencing, highlighting the number of operational taxonomic units (OTUs). Taxonomic analyzes showed that the bacterial community was predominantly and characteristically composed of the phyla Proteobacteria, Actinobacteria, Bacteroidetes, Firmicutes, Verrucomicrobia, and Fibrobacteres, representing the usual microbial profile for the rhizosphere of wheat. Idiomarinaceae, Rheinheimera, Halomonas, and Pseudomonas (a strain of Proteobacteria), together with Gracilibacillus (a strain of Firmicutes Bacilli), were recognized as microbial signatures for the rhizosphere microbiome under saline conditions. This was observed even with unchanged soil type and genotype. These patterns occurred despite the same soil type and genotype, with salinity being the only variable. The collective action of these bacterial phyla in the rhizosphere not only improves nutrient availability but also induces systemic resistance in the plants. This synergistic effect improves plant resistance to salt stress and supports the development of salt-tolerant wheat varieties. These microbial signatures could improve our understanding of plant-microbe interactions and support the development of microbiome-based solutions for salt stress.

Stress-tolerant Bacillus strains for enhancing tomato growth and biocontrol of Fusarium oxysporum under saline conditions: functional and genomic characterization

Soil salinity is a major limiting factor for agricultural crops, which increases their susceptibility to pathogenic attacks. This is particularly relevant for tomato (Solanum lycopersicum), a salt-sensitive crop. Fusarium wilt, caused by Fusarium oxysporum f. sp. lycopersici, is a significant threat to tomato production in both greenhouse and field environments. This study evaluated the salinity tolerance, biocontrol, and plant growth-promoting properties of Bacillus velezensis AF12 and Bacillus halotolerans AF23, isolated from soil affected by underground fires and selected for their resistance to saline conditions (up to 1000 mM NaCl). In vitro assays confirmed that both strains produced siderophores, indole-3-acetic acid (IAA), and proteases and exhibited phosphate solubilization under saline stress (100-200 mM NaCl). AF23 exhibited synergistic interactions with AF12, and inoculation with either strain individually or in combination significantly improved the growth of the Bonny Best tomato cultivar under 200 mM saline stress, leading to increased shoot and root weight, enhanced chlorophyll content, and higher total biomass. The biocontrol potential of AF12 and AF23 was evaluated in tomato plants infected with F. oxysporum. Both strains, individually or combined, increased shoot and root weight, chlorophyll content, and total biomass under non-saline conditions, promoting growth and reducing infection rates under saline stress (100 mM NaCl). Genomic analysis revealed that both strains harbored genes related to salt stress tolerance, biocontrol, and plant growth promotion. In conclusion, Bacillus strains AF23 and AF12 demonstrated strong potential as bioinoculants for enhancing tomato growth and providing protection against F. oxysporum in saline-affected soils.

Unveiling the role of OsSAP17: Enhancing plant resistance to drought and salt

With the intensification of climate change coupled with the inadequate agricultural management in certain regions, plants face numerous challenges due to various abiotic stresses. Stress associated proteins (SAPs) are essential functional genes in plants for coping with stress. This research provides a functional analysis of OsSAP17, a protein belonging to the SAP family in rice. The expression level of OsSAP17 was induced under drought, salt stress and ABA treatment. Subcellular localization analysis revealed that the OsSAP17 protein was distributed in both the cytoplasm and nucleus. The ectopic expression of OsSAP17 significantly increased the capacity to withstand drought and salt stress in both transgenic yeast and Arabidopsis. Additionally, the ectopic expression of OsSAP17 led to notable changes in the expression of Arabidopsis ABA-related genes, including AtNCED3, AtABA2, and AtSnRK2.2. These results indicated that OsSAP17 was able to positively regulate drought and salt tolerance in plants. The insights from this study provided a fundamental understanding of the role of OsSAP17 in abiotic stress response mechanisms and were potentially valuable for breeding crops with enhanced stress tolerance.

A plant endophytic bacterium Burkholderia seminalis strain 869T2 increases plant growth under salt stress by affecting several phytohormone response pathways

BACKGROUND

Due to global warming and gradual climate change, plants are subjected to a wide range of environmental stresses, adversely affecting plant growth and production worldwide. Plants have developed various mechanisms to overpower these abiotic stresses, including salt stress, drought, and high light intensity. Apart from their own defense strategies, plants can get help from the beneficial endophytic bacteria inside host plants and assist them in enduring severe growth conditions. A previously isolated plant endophytic bacteria, Burkholderia seminalis 869T2, from vetiver grass can produce auxin, synthesize siderophore, and solubilize phosphate. The B. seminalis 869T2 can colonize inside host plants and increase the growth of bananas, Arabidopsis, and several leafy vegetables.

RESULTS

We further demonstrated that different growth parameters of Arabidopsis and pak choi plants were significantly increased after inoculating the B. seminalis 869T2 under normal, salt, and drought stress conditions compared to the mock-inoculated plants. Both transcriptome analysis and quantitative real-time PCR results showed that expression levels of genes related to phytohormone signal transduction pathways, including auxin, gibberellin, cytokinin, and abscisic acid were altered in Arabidopsis plants after inoculated with the strain 869T2 under salt stress, in comparison to the mock-inoculated control with salt treatments. Furthermore, the accumulation levels of hydrogen peroxide (H2O2), electrolyte leakage (EL), and malondialdehyde (MDA) were lower in the 869T2-inoculated Arabidopsis and pak choi plants than in control plants under salt and drought stresses.

CONCLUSIONS

The plant endophytic bacterium strain B. seminalis 869T2 may affect various phytohormone responses and reduce oxidative stress damage to increase salt and drought stress tolerances of host plants.

Using Klebsiella sp. and Pseudomonas sp. to Study the Mechanism of Improving Maize Seedling Growth Under Saline Stress

The increasing salinization of cultivated soil worldwide has led to a significant reduction in maize production. Using saline-alkaline-tolerant growth-promoting bacteria (PGPR) in the rhizosphere can significantly improve the saline tolerance of maize and ensure the stability of maize yields, which has become a global research hotspot. This study screened salt-tolerant microorganisms Klebsiella sp. (GF2) and Pseudomonas sp. (GF7) from saline soil to clarify the mechanism in improving the saline tolerance of maize. In this study, different application treatments (GF2, GF7, and GF2 + GF7) and no application (CK) were set up to explore the potential ecological relationships between the saline tolerance of maize seedlings, soil characteristics, and microorganisms. The results showed that co-occurrence network and Zi-Pi analysis identified Klebsiella and Pseudomonas as core microbial communities in the rhizosphere soil of maize seedlings grown in saline soil. The deterministic process of microbial assembly mainly controlled the bacterial community, whereas bacteria and fungi were governed by random processes. The application of saline-alkaline-resistant PGPR under saline stress significantly promoted maize seedling growth, increased the activity of soil growth-promoting enzymes, and enhanced total nitrogen, soil organic carbon, and microbial carbon and nitrogen contents. Additionally, it reduced soil salt and alkali ion concentrations [electrical conductivity (EC) and exchangeable Na+]. Among them, GF2 + GF7 treatment had the best effect, indicating that saline-alkaline-tolerant PGPR could directly or indirectly improve the saline tolerance of maize seedlings by improving the rhizosphere soil ecological environment. EC was the determining factor to promote maize seedling growth under saline-alkaline stress (5.56%; p < 0.01). The results provided an important theoretical reference that deciphers the role of soil factors and microecology in enhancing the saline tolerance of maize.

Effects of coupled application of magnetoelectric activated water and amendments on photosynthetic physiological characteristics and yield of maize in arid regions

Seeking effective improvement agent control measures to enhance the photosynthetic physiological traits and yield levels of spring maize is crucial for efficient green agriculture in arid regions. Therefore, this study was conducted to clarify the effects of coupling improvement agents under magnetoelectric activated water irrigation conditions on the photosynthetic physiological traits, grain nutrients, and yield of spring maize in the arid region of northwest China. Field experiments were set up with three concentrations of growth regulators: 400 times (G1), 500 times (G2), and 600 times (G3), and three amounts of Bacillus subtilis: 15 kg/ha (R1), 45 kg/ha (R2), and 75 kg/ha (R3), along with a control group CK, making a total of 10 treatments applied in the field experiment. The results indicate that under magnetoelectric activated water irrigation, coupling improvement agents significantly enhance the photosynthetic traits, grain nutrients, and yield of spring maize in arid areas. With the coupling of improvement agents, the rectangular hyperbola correction model showed a good fit for the light response curve (R2 >0.992). Pnmax was significantly increased (7.37%~37.46%) and was highly correlated with yield (P<0.01). The entropy-weight TOPSIS comprehensive evaluation analysis found that the G2R2 treatment is the optimal improvement agent coupling measure for efficient production of spring maize in arid regions. This treatment yielded 12.68 t/ha and increased 100-kernel weight, grains per spike, and soluble sugar content by 21.3%, 8.22%, and 63.81%, respectively, representing the best balance of quality and high yield. The results of this study provide theoretical references and technical support for the high-quality and efficient production of spring maize in China's arid regions.

Effects of salt stress on plant and rhizosphere bacterial communities, interaction patterns, and functions

Introduction

Salt stress significantly affects plant growth, and Na+ has gained attention for its potential to enhance plant adaptability to saline conditions. However, the interactions between Na+, plants, and rhizosphere bacterial communities remain unclear, hindering a deeper understanding of how Na+ contributes to plant resilience under salt stress.

Methods

This study aimed to investigate the mechanisms through which Na+ promotes alfalfa's adaptation to salt stress by modifying rhizosphere bacterial communities. We examined the metabolic activity and community composition of both plant and rhizosphere bacteria under Na+ treatment.

Results and discussion

Our results revealed significant changes in the metabolism and community composition of both plant and rhizosphere bacteria following Na+ addition. Na+ not only promoted the growth of rhizosphere bacteria but also induced shifts in the plant-associated bacterial community, increasing the abundance of bacterial species linked to alfalfa's resistance to salt stress. Furthermore, the chemical characteristics of alfalfa were strongly correlated with the composition and network complexity of both plant and rhizosphere bacterial communities. These interactions suggest that Na+ plays a crucial role in enhancing alfalfa's adaptability to salt stress by fostering beneficial bacterial communities in the rhizosphere. This finding highlights the potential of leveraging Na+ interactions with plant-microbe systems to improve crop resilience and productivity in saline agricultural environments.

Plant Growth-Promoting and Herbicidal Bacteria as Potential Bio-Based Solutions for Agriculture in Desertic Regions

The region of Arica and Parinacota hosts unexplored remote sites with unique characteristics suitable for developing novel agricultural bioproducts. Notable locations include Jurasi Hot Springs, Polloquere Hot Springs, and Amuyo Lagoons, featuring open pools fed by thermal mountain springs. These geothermal sites harbor bacteria with plant growth-promoting activities, particularly interesting to the strains J19, TP22, A20, and A3. These bacteria possess in vitro plant growth-promoting traits, the ability to produce hydrolytic enzymes, and the capacity to inhibit phytopathogenic fungi. Moreover, they can tolerate different concentrations of NaCl and boron, making them suitable for developing new agricultural bioproducts for arid environments. The bacterial strains A3 and A20 have a positive effect on the growth of the aerial part of tomato plants (increased stem length, fresh and dry weight), with a significant increment in proline concentration and chlorophyll A and B content under saline conditions. Meanwhile, the strains J19 and TP22 exhibit herbicidal activity against Cenchrus echinatus by reducing root elongation and germination of the weed. These strains possess plant growth-promoting traits and improve plant resistance to salinity stress. They are promising candidates for developing innovative bio-based agricultural products suited to arid and semi-arid regions.

The Microbial Diversity of Biological Moss Crust: Application in Saline-Alkali Soil Management

Soil salinization poses a substantial threat to global food security, particularly under the influence of climate change, and is recognized as one of the most urgent challenges in land degradation. This study aims to elucidate the challenges associated with managing arid and semi-arid saline-alkali lands in China's Ningxia province and propose feasible solutions. To assess moss crust colonization, we measured changes in organic matter and chlorophyll levels. Additionally, we investigated the impact of an interlayer composed of Goji berry root bark using liquid chromatography-mass spectrometry analysis, biological enzyme activity analysis, and metagenomic sequencing. A total of 45 endophytes were isolated from the moss crust. The most significant colonization of moss crusts was observed when the Goji berry root bark was used as the interlayer, resulting in a significant increase in chlorophyll content. Several responses were identified as pivotal factors facilitating moss crust growth when the Goji berry root bark was used as the interlayer. In saline-alkali soil, the Goji berry root bark interlayer increased the activities of sucrase, urease, and alkaline phosphatase. Metagenomic data analysis revealed variations in the relative abundance of microorganisms at the phylum level, although these differences were not statistically significant. Evaluation of the impact of physical isolation and moss crust transplantation on the ecological restoration of saline-alkali soil using liquid chromatography-tandem mass spectrometry and metagenomic sequencing indicated that the Goji berry root bark as a physical isolation method promotes moss crust colonization in saline-alkali soil and increases soil organic matter and nutrient elements, offering valuable insights for the ecological management of saline-alkali land and serving as a reference for future research in this field.

Improving plant salt tolerance through Algoriphagus halophytocola sp. nov., isolated from the halophyte Salicornia europaea

Salicornia europaea, commonly known as glasswort, thrives in reclaimed land and coastal areas with high salinity, demonstrating remarkable adaptation to the arid conditions of such environments. Two aerobic, Gram-stain-negative, non-motile, rod-shaped bacterial strains, designated TR-M5T and TR-M9, were isolated from the root of Salicornia europaea plants. These bacteria exhibit plant growth-promoting and salt tolerance-enhancing abilities, which have not been reported in other species of the genus. Both strains produce indole-3-acetic acid (IAA), a plant growth hormone, and synthesize proline, which functions as an osmoprotectant. Additionally, they possess gelatinase and cellulase activities. Cells grow in temperatures from 4 to 42°C (optimum 25°C), pH levels from 6.0 to 9.0 (optimum 7.0), and NaCl concentrations from 0 to 8.0% (optimum 6.0%). The average nucleotide identity and digital DNA-DNA hybridization values of strain TR-M5T with the most closely related type strains for which whole genomes are publicly available were 74.05-77.78% and 18.6-23.1%, respectively. Phylogenetic analysis of their 16S rRNA gene sequences revealed that strains TR-M5T and TR-M9 belong to the genus Algoriphagus. A. locisalis exhibited the highest similarity, sharing a sequence identity of 98.1%. The genomes of TR-M5T and TR-M9 exhibit a G + C content of 43 mol%. This study specifically focuses on the identification and characterization of strain TR-M5T as a novel species within the genus Algoriphagus, which we propose to name Algoriphagus halophytocola sp. nov., highlighting its potential role in enhancing plant growth and salt tolerance in saline environments. The type strain is TR-M5T (KCTC 92720T = GDMCC 1.3797T).

Role of organic amendments in improving the morphophysiology and soil quality of Setaria italica under salinity

Salinity negatively impacts soil fertility by impairing the development and physiological functions of foxtail millet plants. Organic amendments have emerged as a viable solution in the reclamation and management of salinity inflicted soils and improve the performance of crop. In this regard, a pot experiment was carried out to examine the effect of organic amendments (OAs) on soil quality and its influence on the growth and physiology of foxtail millet under saline and non-saline condition. The findings indicated that under salt stress conditions, the levels of proline, hydrogen peroxide (H2O2), and electrolyte leakage (EL) risen, whilst other physiological parameters decrease in foxtail millet. However, the addition of OAs, particularly dhaincha and biochar (BC), has shown a promising salt tolerant amendment among others. Its addition improved the growth performance of salinity-stressed plants, including plant height, fresh and dry biomass, simultaneously decreased sodium ion (Na+) and improved calcium (Ca2+), potassium (K+), and nitrate ion (NO3 -). They also increased proline build up by 6-17 %, reduced H2O2 (19-38 %) and malondialdehyde (16-18 %). Furthermore, they elevated the relative water content (RWC) (25 %), chlorophyll content, and reduced EL (29-50 %). Once more, dhaincha and BC enhanced the number of rhizobia, phosphorus-solubilizing bacteria (PSB) and overall bacterial population in the soil. In saline soil, daincha and BC could enhance soil organic matter (628 %), total nitrogen (1630 %), available phosphorus (32-38 %), and exchangeable potassium (54-73 %). A potential strategy for improving setaria italica performance under salt is suggested to be the following order, dhaincha > biochar > vermicompost > duckweed. The study would assist stakeholders in these salinity-prone areas in strategizing the use of OAs to their fallow land for cultivation and agricultural activities.

Bacillus subtilis Strain YJ-15, Isolated from the Rhizosphere of Wheat Grown under Saline Conditions, Increases Soil Fertility and Modifies Microbial Community Structure

Soil salinization during wheat cultivation considerably diminishes soil fertility and impedes wheat growth, primarily due to rhizosphere microbial community changes. Our study investigates the application of Bacillus subtilis YJ-15, a strain isolated from the rhizosphere of wheat cultivated in salinized soil, as a soil remediation agent. This strain has demonstrated significant salt tolerance, disease suppression capabilities, and growth-promoting attributes in previous studies. The wheat rhizosphere was examined to assess the impact of Bacillus subtilis YJ-15 on microbial community composition and soil fertility. Fertility of soil in saline soil was significantly increased by inoculating wheat with YJ-15. The microbial community structure within the wheat rhizosphere inoculated with Bacillus subtilis YJ-15 was analyzed through sequencing on the Illumina MiSeq platform. Phyla Proteobacteria and Acidobacteria were identified as the dominant bacteria. Basidiomycota, Mortierellomycota, and Ascomycota dominated the fungal phyla. Among the bacterial genera, Pseudomonas, Arthrobacter, and Bacillus were predominant. The predominant fungal genera included Alternaria, Cephalotrichum, Mortierella, and Chaetomium. A significant increase in Gaiella and Haliangium levels was observed in the YJ group compared to the control group. Additionally, the fungal genera Epicoccum, Sporidiobolus, and Lecythophora have significantly increased in YJ abundance. One of the potential benefits of Bacillus subtilis YJ-15 in the cultivation of wheat on salinized land is its ability to enhance the rhizosphere microbial community structure and improve soil fertility.

Physiological and Molecular Mechanisms of Rice Tolerance to Salt and Drought Stress: Advances and Future Directions

Rice, a globally important food crop, faces significant challenges due to salt and drought stress. These abiotic stresses severely impact rice growth and yield, manifesting as reduced plant height, decreased tillering, reduced biomass, and poor leaf development. Recent advances in molecular biology and genomics have uncovered key physiological and molecular mechanisms that rice employs to cope with these stresses, including osmotic regulation, ion balance, antioxidant responses, signal transduction, and gene expression regulation. Transcription factors such as DREB, NAC, and bZIP, as well as plant hormones like ABA and GA, have been identified as crucial regulators. Utilizing CRISPR/Cas9 technology for gene editing holds promise for significantly enhancing rice stress tolerance. Future research should integrate multi-omics approaches and smart agriculture technologies to develop rice varieties with enhanced stress resistance, ensuring food security and sustainable agriculture in the face of global environmental changes.

Growth and protein response of rice plant with plant growth-promoting rhizobacteria inoculations under salt stress conditions

Soil salinity has been one of the significant barriers to improving rice production and quality. According to reports, Bacillus spp. can be utilized to boost plant development in saline soil, although the molecular mechanisms behind the interaction of microbes towards salt stress are not fully known. Variations in rice plant protein expression in response to salt stress and plant growth-promoting rhizobacteria (PGPR) inoculations were investigated using a proteomic method and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Findings revealed that 54 salt-responsive proteins were identified by mass spectrometry analysis (LC-MS/MS) with the Bacillus spp. interaction, and the proteins were functionally classified as gene ontology. The initial study showed that all proteins were labeled by mass spectrometry analysis (LC-MS/MS) with Bacillus spp. interaction; the proteins were functionally classified into six groups. Approximately 18 identified proteins (up-regulated, 13; down-regulated, 5) were involved in the photosynthetic process. An increase in the expression of eight up-regulated and two down-regulated proteins in protein synthesis known as chaperones, such as the 60 kDa chaperonin, the 70 kDa heat shock protein BIP, and calreticulin, was involved in rice plant stress tolerance. Several proteins involved in protein metabolism and signaling pathways also experienced significant changes in their expression. The results revealed that phytohormones regulated the manifestation of various chaperones and protein abundance and that protein synthesis played a significant role in regulating salt stress. This study also described how chaperones regulate rice salt stress, their different subcellular localizations, and the activity of chaperones.

Plant growth-promoting rhizobacteria Pseudomonas aeruginosa HG28-5 improves salt tolerance by regulating Na+/K+ homeostasis and ABA signaling pathway in tomato

Salinity stress badly restricts the growth, yield and quality of vegetable crops. Plant growth-promoting rhizobacteria (PGPR) is a friendly and effective mean to enhance plant growth and salt tolerance. However, information on the regulatory mechanism of PGPR on vegetable crops in response to salt stress is still incomplete. Here, we screened a novel salt-tolerant PGPR strain Pseudomonas aeruginosa HG28-5 by evaluating the tomatoes growth performance, chlorophyll fluorescence index, and relative electrolyte leakage (REL) under normal and salinity conditions. Results showed that HG28-5 colonization improved seedling growth parameters by increasing the plant height (23.7%), stem diameter (14.6%), fresh and dry weight in the shoot (60.3%, 91.1%) and root (70.1%, 92.5%), compared to salt-stressed plants without colonization. Likewise, HG28-5 increased levels of maximum photochemical efficiency of PSII (Fv/Fm) (99.3%), the antioxidant enzyme activities as superoxide dismutase (SOD, 85.5%), peroxidase (POD, 35.2%), catalase (CAT, 20.6%), and reduced the REL (48.2%), MDA content (41.3%) and ROS accumulation in leaves of WT tomatoes under salt stress in comparison with the plants treated with NaCl alone. Importantly, Na+ content of HG28-5 colonized salt-stressed WT plants were decreased by15.5% in the leaves and 26.6% in the roots in the corresponding non-colonized salt-stressed plants, which may be attributed to the higher K+ concentration and SOS1, SOS2, HKT1;2, NHX1 transcript levels in leaves of colonized plants under saline condition. Interestingly, increased abscisic acid (ABA) content and upregulation of ABA pathway genes (ABA synthesis-related genes NCED1, NCED2, NCED4, NECD6 and signal genes ABF4, ABI5, and AREB) were observed in HG28-5 inoculated salt-stressed WT plants. ABA-deficient mutant (not) with NCED1 deficiency abolishes the effect of HG28-5 on alleviating salt stress in tomato, as exhibited by the substantial rise of REL and ROS accumulation and sharp drop of Fv/Fm in the leaves of not mutant plants. Notably, HG28-5 colonization enhances tomatoes fruit yield by 54.9% and 52.4% under normal and saline water irrigation, respectively. Overall, our study shows that HG28-5 colonization can significantly enhance salt tolerance and improved fruit yield by a variety of plant protection mechanism, including reducing oxidative stress, regulating plant growth, Na+/K+ homeostasis and ABA signaling pathways in tomato. The findings not only deepen our understanding of PGPR regulation plant growth and salt tolerance but also allow us to apply HG28-5 as a microbial fertilizer for agricultural production in high-salinity areas.

Mechanisms on salt tolerant of Paenibacillus polymyxa SC2 and its growth-promoting effects on maize seedlings under saline conditions

Soil salinity negatively affects microbial communities, soil fertility, and agricultural productivity and has become a major agricultural problem worldwide. Plant growth-promoting rhizobacteria (PGPR) with salt tolerance can benefit plant growth under saline conditions and diminish the negative effects of salt stress on plants. In this study, we aimed to understand the salt-tolerance mechanism of Paenibacillus polymyxa at the genetic and metabolic levels and elucidate the mechanism of strain SC2 in promoting maize growth under saline conditions. Under salt stress, we found that strain SC2 promoted maize seedling growth, which was accompanied by a significant upregulation of genes encoding for the biosynthesis of peptidoglycan, polysaccharide, and fatty acid, the metabolism of purine and pyrimidine, and the transport of osmoprotectants such as trehalose, glycine betaine, and K+ in strain SC2. To further enhance the salt resistance of strain SC2, three mutants (SC2-11, SC2-13, and SC2-14) with higher capacities for salt resistance and exopolysaccharide synthesis were obtained via atmospheric and room-temperature plasma mutagenesis. In saline-alkaline soil, the mutants showed better promoting effect on maize seedlings than wild-type SC2. The fresh weight of maize seedlings was increased by 68.10% after treatment with SC2-11 compared with that of the control group. The transcriptome analysis of maize roots demonstrated that SC2 and SC2-11 could induce the upregulation of genes related to the plant hormone signal transduction, starch and sucrose metabolism, reactive oxygen species scavenging, and auxin and ethylene signaling under saline-alkaline stress. In addition, various transcription factors, such as zinc finger proteins, ethylene-responsive-element-binding protein, WRKY, myeloblastosis proteins, basic helix-loop-helix proteins, and NAC proteins, were up-regulated in response to abiotic stress. Moreover, the microbial community composition of maize rhizosphere soil after inoculating with strain SC2 was varied from the one after inoculating with mutant SC2-11. Our results provide new insights into the various genes involved in the salt resistance of strain SC2 and a theoretical basis for utilizing P. polymyxa in saline-alkaline environments.

Halophytic Bacterial Endophyte Microbiome from Coastal Desert-Adapted Wild Poaceae Alleviates Salinity Stress in the Common Wheat Triticum aestivum L

Abiotic stresses threaten the strategic crops of Poaceae (Gramineae) worldwide. Habitat-adapted microbiome of wild plants has the potential to alleviate abiotic stresses in alternate hosts. Persian Gulf's coastal deserts are colonized by halophyte plants hosting habitat-adapted halophytic microbiota. Here, endophytic bacteria from wild Poaceae in coastal deserts of the north Persian Gulf at Hormozgan province, Iran, were isolated and screened for mitigating salinity stress in wheat. Accordingly, seven dominant species of wild Poaceae in the region, i.e., Aeloropus lagopoides, Aeloropus litiralis, Chrysopogon aucheri, Cymbopogon olivieri, Desmostachya sp., Halopayrum mucronatum, and Sporbuls arabicus, were explored. In total, 367 endophytic bacteria were isolated, 90 of which tolerated 2.5-M NaCl. Of these, 38 strains were selected based on their bioactivity and applied for in vitro wheat-interaction assays under 250-mM NaCl stress. Five superior strains promoted seed germination and growth indices in rain-fed winter wheat cv. Sardari, i.e., Bacillus subtilis B14, B19, & B27, Bacillus sp. B21, and Bacillus licheniformis Ba38. In planta assays in saline soil (2.7 dS m-1) using the superior strains indicated that Bacillus sp. B21 and Bacillus licheniformis Ba38 increased germination and root and shoot lengths and their dry and fresh weights in wheat seedlings. Moreover, phenolics and flavonoids contents of wheat seedlings were influenced by endophyte application. Thus, the coastal desert-adapted microbiome of wild Poaceae could alleviate abiotic stress and promote growth in cultivated species of Poaceae, such as wheat.

Biological roles of soil microbial consortium on promoting safe crop production in heavy metal(loid) contaminated soil: A systematic review

Heavy metal(loid) (HM) pollution of agricultural soils is a growing global environmental concern that affects planetary health. Numerous studies have shown that soil microbial consortia can inhibit the accumulation of HMs in crops. However, our current understanding of the effects and mechanisms of inhibition is fragmented. In this review, we summarise extant studies and knowledge to provide a comprehensive view of HM toxicity on crop growth and development at the biological, cellular and the molecular levels. In a meta-analysis, we find that microbial consortia can improve crop resistance and reduce HM uptake, which in turn promotes healthy crop growth, demonstrating that microbial consortia are more effective than single microorganisms. We then review three main mechanisms by which microbial consortia reduce the toxicity of HMs to crops and inhibit HMs accumulation in crops: 1) reducing the bioavailability of HMs in soil (e.g. biosorption, bioaccumulation and biotransformation); 2) improving crop resistance to HMs (e.g. facilitating the absorption of nutrients); and 3) synergistic effects between microorganisms. Finally, we discuss the prospects of microbial consortium applications in simultaneous crop safety production and soil remediation, indicating that they play a key role in sustainable agricultural development, and conclude by identifying research challenges and future directions for the microbial consortium to promote safe crop production.

Integrated Genomics and Transcriptomics Provide Insights into Salt Stress Response in Bacillus subtilis ACP81 from Moso Bamboo Shoot (Phyllostachys praecox) Processing Waste

Salt stress is detrimental to the survival of microorganisms, and only a few bacterial species produce hydrolytic enzymes. In this study, we investigated the expression of salt stress-related genes in the salt-tolerant bacterial strain Bacillus subtilis ACP81, isolated from bamboo shoot processing waste, at the transcription level. The results indicate that the strain could grow in 20% NaCl, and the sub-lethal concentration was 6% NaCl. Less neutral protease and higher cellulase and β-amylase activities were observed for B. subtilis ACP81 under sub-lethal concentrations than under the control concentration (0% NaCl). Transcriptome analysis showed that the strain adapted to high-salt conditions by upregulating the expression of genes involved in cellular processes (membrane synthesis) and defense systems (flagellar assembly, compatible solute transport, glucose metabolism, and the phosphotransferase system). Interestingly, genes encoding cellulase and β-amylase-related (malL, celB, and celC) were significantly upregulated and were involved in starch and sucrose metabolic pathways, and the accumulated glucose was effective in mitigating salt stress. RT-qPCR was performed to confirm the sequencing data. This study emphasizes that, under salt stress conditions, ACP81 exhibits enhanced cellulase and β-amylase activities, providing an important germplasm resource for saline soil reclamation and enzyme development.

Unraveling lipid peroxidation-mediated regulation of redox homeostasis for sustaining plant health

Lipid peroxidation (LPO) is a complex process that, depending on the context, can either result in oxidative injury or promote redox homeostasis. LPO is a series of reactions in which polyunsaturated fatty acids are attacked by free radicals that result in the synthesis of lipid peroxides. LPO can alter membrane fluidity and operation and produce secondary products that amplify oxidative stress. LPO can activate cellular signaling pathways that promote antioxidant defense mechanisms that provide oxidative stress protection by elevating antioxidant enzyme action potentials. Enzymatic and nonenzymatic mechanisms tightly regulate LPO to prevent excessive LPO and its adverse consequences. This article emphasizes the dual nature of LPO as a mechanism that can both damage cells and regulate redox homeostasis. In addition, it also highlights the major enzymatic and nonenzymatic mechanisms that tightly regulate LPO to prevent excessive oxidative damage. More importantly, it emphasizes the importance of understanding the cellular and biochemical complexity of LPO for developing strategies targeting this process for efficient management of plant stress.

Advances in Identifying the Mechanisms by Which Microorganisms Improve Barley Salt Tolerance

As the global human population continues to increase, the use of saline-alkali land for food production is an important consideration for food security. In addition to breeding or cultivating salt-tolerant crop varieties, microorganisms are increasingly being evaluated for their ability to improve plant salt tolerance. Barley is one of the most important and salt-tolerant cereal crops and is a model system for investigating the roles of microorganisms in improving plant salt tolerance. However, a comprehensive review of the mechanisms by which microorganisms improve barley salt tolerance remains lacking. In this review, the mechanisms of barley salt tolerance improvement by microorganisms are summarized, along with a discussion of existing problems in current research and areas of future research directions. In particular, with the development of sequencing technology and the great reduction of prices, the use of omics can not only comprehensively evaluate the role of microorganisms but also evaluate the impact of the microbiome on plants, which will provide us with many opportunities and challenges in this research area.

Exo-polysaccharide producing bacteria can induce maize plant growth and soil health under saline conditions

Salt tolerant plant growth boosting rhizobacteria can play an important function in plant salinity stress mitigation. In the current investigation, only two rhizobacterial isolates out of 68 produced exo-polysaccharide at the fastest rate and exhibited plant growth promoting properties such as IAA, CAT, APX production, and phosphate solubilization at 6% NaCl (w/v) concentration. Both isolates had synergistic PGP features and were compatible with one another. Isolate SP-20 was identified as Kluyvera sp. and SP-203 was identified as Enterobacter sp. -by 16SrDNA sequencing. After 30, 60, and 90 days, the combination of SP-20 and SP-203 enhanced the physicochemical parameters in the maize plant in comparison to the control. By increasing soil enzymes like DHA and PPO, both isolates significantly improved the soil health matrix. When a group of these isolates were inoculated into 1% and 2% NaCl (w/v) supplemented soil, the absorption of Na in the shoot and root of maize plants was inhibited by around 50%. The BCF values for all treatments were less than TF, and the values of BCF and TF were less than one. Therefore, the present study illustrated that the novel native isolates play a remarkable role to mitigate salinity stress in maize plant.

Deciphering the potential of a plant growth promoting endophyte Rhizobium sp. WYJ-E13, and functional annotation of the genes involved in the metabolic pathway

Plant growth-promoting rhizobacteria (PGPR) are well-acknowledged root endophytic bacteria used for plant growth promotion. However, which metabolites produced by PGPR could promote plant growth remains unclear. Additionally, which genes are responsible for plant growth-promoting traits is also not elucidated. Thus, as comprehensive understanding of the mechanism of endophyte in growth promotion is limited, this study aimed to determine the metabolites and genes involved in plant growth-promotion. We isolated an endophytic Rhizobium sp. WYJ-E13 strain from the roots of Curcuma wenyujin Y.H. Chen et C. Ling, a perennial herb and medicinal plant. The tissue culture experiment showed its plant growth-promoting ability. The bacterium colonization in the root was confirmed by scanning electron microscopy and paraffin sectioning. Furthermore, it was noted that the WYJ-E13 strain produced cytokinin, anthranilic acid, and L-phenylalanine by metabolome analysis. Whole-genome analysis of the strain showed that it consists of a circular chromosome of 4,350,227 bp with an overall GC content of 60.34%, of a 2,149,667 bp plasmid1 with 59.86% GC, and of a 406,180 bp plasmid2 with 58.05% GC. Genome annotation identified 4,349 putative protein-coding genes, 51 tRNAs, and 9 rRNAs. The CDSs number allocated to the Kyoto Encyclopedia of Genes and Genomes, Gene Ontology, and Clusters of Orthologous Genes databases were 2027, 3,175 and 3,849, respectively. Comparative genome analysis displayed that Rhizobium sp. WYJ-E13 possesses the collinear region among three species: Rhizobium acidisoli FH23, Rhizobium gallicum R602 and Rhizobium phaseoli R650. We recognized a total set of genes that are possibly related to plant growth promotion, including genes involved in nitrogen metabolism (nifU, gltA, gltB, gltD, glnA, glnD), hormone production (trp ABCDEFS), sulfur metabolism (cysD, cysE, cysK, cysN), phosphate metabolism (pstA, pstC, phoB, phoH, phoU), and root colonization. Collectively, these findings revealed the roles of WYJ-E13 strain in plant growth-promotion. To the best of our knowledge, this was the first study using whole-genome sequencing for Rhizobium sp. WYJ-E13 associated with C. wenyujin. WYJ-E13 strain has a high potential to be used as Curcuma biofertilizer for sustainable agriculture.

Organic Amendments for Mitigation of Salinity Stress in Plants: A Review

Natural and/or human-caused salinization of soils has become a growing problem in the world, and salinization endangers agro-ecosystems by causing salt stress in most cultivated plants, which has a direct effect on food quality and quantity. Several techniques, as well as numerous strategies, have been developed in recent years to help plants cope with the negative consequences of salt stress and mitigate the impacts of salt stress on agricultural plants. Some of them are not environmentally friendly. In this regard, it is crucial to develop long-term solutions that boost saline soil productivity while also protecting the ecosystem. Organic amendments, such as vermicompost (VC), vermiwash (VW), biochar (BC), bio-fertilizer (BF), and plant growth promoting rhizobacteria (PGPR) are gaining attention in research. The organic amendment reduces salt stress and improves crops growth, development and yield. The literature shows that organic amendment enhances salinity tolerance and improves the growth and yield of plants by modifying ionic homeostasis, photosynthetic apparatus, antioxidant machineries, and reducing oxidative damages. However, the positive regulatory role of organic amendments in plants and their stress mitigation mechanisms is not reviewed adequately. Therefore, the present review discusses the recent reports of organic amendments in plants under salt stress and how stress is mitigated by organic amendments. The current assessment also analyzes the limitations of applying organic amendments and their future potential.