Plant Abiotic Stress Resistance Research Articles

PLANT-GROWTH-PROMOTING AND ANTIFUNGAL ASSET OF INDIGENOUS DROUGHT-TOLERANT RHIZOBACTERIA ISOLATED FROM OLIVE (Olea europaea L.) RHIZOSPHERE

Faced with global environmental challenges, the quest for sustainable food production has gathered momentum. While abiotic stresses adversely affect plant health and productivity, Verticillium wilt causes considerable yield losses worldwide, particularly in crops such as olive. Recently, drought-tolerant bacteria have been used to alleviate both abiotic stress and pathogen pressure in crops. In this context, our work focuses on the isolation of tolerant indigenous rhizobacteria to mitigate these challenges by investigating their role in biocontrol and abiotic stress tolerance. Thus, a total of 94 rhizobacterial strains were isolated from the rhizospheres of olive trees in southeastern Morocco and characterized to identify tolerant plant growth-promoting rhizobacteria that inhibit Verticillium dahliae. 24 strains demonstrated in vitro suppression of Verticillium dahliae Klebahn, and exhibited tolerance to different abiotic stresses (drought, salinity, and high temperature). In addition, they proved xerotolerant (Aw ≤ 0.91), halotolerant (≥10% NaCl), and thermotolerant (≥ 55°C) capabilities. Beyond, these isolates showcased multifaceted plant growth-promoting traits, such as phosphate solubilization and significant synthesis of essential bioactive compounds like siderophores, indole-3-acetic acid and hydrolytic enzymes. Evaluating outcomes, three standout rhizobacterial isolates emerged due to their exceptional stress tolerance, unique plant growth-promoting qualities, and potent antagonistic potential. Molecular analysis identified them as Bacillus paranthracis (OZ-60) and Bacillus licheniformis (OZ-48 and OZ-77) through 16S rRNA sequencing. Besides enhancing plant abiotic stress resistance, these isolates hold promise in bolstering the sustainability of olive cultivation and fortifying plant defenses against pathogens.

Exogenous citric acid improves growth and yield by concerted modulation of antioxidant defense system in brinjal (Solanum melongena L.) under salt-stress

Brinjal is sensitive to salinity, a common factor responsible for reducing its biomass and yield components. Recent research has demonstrated that citric acid/citrates can provide abiotic stress resistance in plants. In this study, Brinjal variety Pusakranti was treated with four concentrations of CA at 0, 100, 200, and 300 ppm applied foliarly under two levels of salt stress (0 mM and 60 mM NaCl) during spring 2021 with four replication per treatment. Salt stress reduced plant growth and yield attributes, pigments as well as metabolites in plants. Antioxidant enzyme activities of the plant increased compared to the non-stressed plants. While 300 ppm CA concentrations oenhanced the shoot and root fresh biomass (75 % and 71.8 %) and dry biomass (82.5 % and 40.7 %), while 200 ppm CA application increased the fruits count by 50 %, fruit diameter by 49 % and leaf photosynthetic pigments by 61 % compared to only salt-stressed plants. Similarly, CA application enhanced the antioxidants both enzymatic and non-enzymatic such as catalase by 42 %, peroxidase by 66 %, superoxide dismutase by 44 %, polyphenol oxidase by 50 % and Glutathione peroxidase by 37 % compared to only salt stressed plants. Furthermore, 300 ppm CA application also promoted the content of primary metabolites such as total protein content by 75 % and total free amino acids by 32 % as well as improvement in secondary metabolites such as total phenols by 31 % and flavonoids by 96 % compared to only salt treated plants. Overall, the above described results suggested that the foliarly applied CA(200 ppm) is a proficient approach which effectively counteract salt stress in brinjal by improving plant biomass, pigments, primary and secondary metabolites as well as modulating the the antioxidant defense system of the studied plant.

A novel PGPR strain homologous to Beijerinckia fluminensis induces biochemical and molecular changes involved in Arabidopsis thaliana salt tolerance

The use of PGPR is widely accepted as a promising tool for a more sustainable agricultural production and improved plant abiotic stress resistance. This study tested the ability of PVr_9, a novel bacterial strain, homologous to Beijerinckia fluminensis, to increase salt stress tolerance in A. thaliana. In vitro plantlets inoculated with PVr_9 and treated with 150 mM NaCl showed a reduction in primary root growth inhibition compared to uninoculated ones, and a leaf area significantly less affected by salt. Furthermore, salt-stressed PVr_9-inoculated plants had low ROS and 8-oxo-dG, osmolytes, and ABA content along with a modulation in antioxidant enzymatic activities. A significant decrease in Na+ in the leaves and a corresponding increase in the roots were also observed in salt-stressed inoculated plants. SOS1, NHX1 genes involved in plant salt tolerance, were up-regulated in PVr_9-inoculated plants, while different MYB genes involved in salt stress signal response were down-regulated in both roots and shoots. Thus, PVr_9 was able to increase salt tolerance in A. thaliana, thereby suggesting a role in ion homeostasis by reducing salt stress rather than inhibiting total Na+ uptake. These results showed a possible molecular mechanism of crosstalk between PVr_9 and plant roots to enhance salt tolerance, and highlighted this bacterium as a promising PGPR for field applications on agronomical crops.

MicroRNA162 regulates stomatal conductance in response to low night temperature stress via abscisic acid signaling pathway in tomato

MicroRNAs (miRNAs) mediate the degradation of target mRNA and inhibit mRNA translation to regulate gene expression at the transcriptional and post-transcriptional levels in response to environmental stress in plants. We characterized the post-transcriptional mechanism by deep sequencing small RNA (sRNA) to examine how miRNAs were involved in low night temperature (LNT) stress in tomato and whether the molecular mechanism depended on the abscisic acid (ABA) signaling pathway. We annotated conserved miRNAs and novel miRNAs with four sRNA libraries composed of wild-type (WT) tomato plants and ABA-deficient mutant (sit) plants under normal growth and LNT stress conditions. Reverse genetics analysis suggested that miR162 participated in LNT resistance and the ABA-dependent signaling pathway in tomato. miR162-overexpressing (pRI-miR162) and miR162-silenced (pRNAi-miR162) transgenic tomato plants were generated to evaluate miR162 functions in response to LNT stress. miR162 deficiency exhibited high photosynthetic capacity and regulated stomatal opening, suggesting negative regulation of miR162 in the ABA-dependent signaling pathway in response to LNT stress. As feedback regulation, miR162 positively regulated ABA to maintain homeostasis of tomato under diverse abiotic stresses. The mRNA of DICER-LIKE1 (DCL1) was targeted by miR162, and miR162 inhibited DCL1 cleavage in LNT response, including the regulation of miRNA160/164/171a and their targets. The DCL1-deficient mutants (dcl1) with CRISPR/Cas9 prevented stomatal opening to influence photosynthesis in the ABA signaling pathway under LNT stress. Finally, we established the regulatory mechanism of ABA-miR162-DCL1, which systematically mediated cold tolerance in tomato. This study suggests that post-transcriptional modulators acted as systemic signal responders via the stress hormone signaling pathway, and the model at the post-transcriptional level presents a new direction for research in plant abiotic stress resistance.

Abiotic stress tolerance in plants: a fascinating action of defense mechanisms.

Climate fluctuation mediated abiotic stress consequences loss in crop yields. These stresses have a negative impact on plant growth and development by causing physiological and molecular changes. In this review, we have attempted to outline recent studies (5years) associated with abiotic stress resistance in plants. We investigated the various factors that contribute to coping with abiotic challenges, such as transcription factors (TFs), microRNAs (miRNAs), epigenetic changes, chemical priming, transgenic breeding, autophagy, and non-coding RNAs. Stress responsive genes are regulated mostly by TFs, and these can be used to enhance stress resistance in plants. Plants express some miRNA during stress imposition that act on stress-related target genes to help them survive. Epigenetic alterations govern gene expression and facilitate stress tolerance. Chemical priming enhances growth in plants by modulating physiological parameters. Transgenic breeding enables identification of genes involved in precise plant responses during stressful situations. In addition to protein coding genes, non-coding RNAs also influence the growth of the plant by causing alterations at gene expression levels. For achieving sustainable agriculture for a rising world population, it is crucial to develop abiotic-resistant crops with anticipated agronomical traits. To achieve this objective, understanding the diverse mechanisms by which plants protect themselves against abiotic stresses is imperative. This review emphasizes on recent progress and future prospects for abiotic stress tolerance and productivity in plants.

Freezing transcriptome analysis showed that GhZAT10 regulates freezing tolerance through a partially CBF-dependent pathway in upland cotton (Gossypium hirsutum L.)

Cotton is an important economic crop worldwide, which is mainly distributed in the tropics and subtropics; therefore, it is highly sensitive to low temperatures. ZAT and CBF play important roles in plant growth and stress responses. However, few studies have investigated the role of these genes in freezing tolerance of cotton, and the interaction between these two remains unclear. In this study, KN27–3 cotton with strong freezing tolerance was selected from 17 cotton varieties. RNA-sequencing analysis showed that KN27–3 cotton presented 6747 differentially expressed genes (DEGs), which were mostly upregulated at the early time points after the treatments. Weighted gene co-expression network analysis and Gene Ontology enrichment analysis showed that various DEGs were involved in plant abiotic stress resistance, including SRK2I, ELF3, WRKY70, and TPS6. Moreover, 31 early upregulated transcription factors, including CBF and ZAT, were identified after 15 min of freezing treatment. Such significant upregulation at the early stage suggested that GhCBF4 (Gh_A12G2357) and GhZAT10 (Gh_D05G2011) play important roles in cotton freezing stress. Virus-induced gene silencing indicated that GhCBF4- and GhZAT10-silenced plants exhibit significant freezing-sensitive phenotypes. Biofilm interferometry and dual luciferase experiments showed that GhCBF4 regulated transcription by directly binding to a CRT/DRE motif within the GhZAT10 promoter. In summary, GhZAT10 and GhCBF4 regulated plant freezing tolerance, and GhZAT10 expression was at least partially regulated by CBF. These findings expand our current understanding of the mechanisms underlying GhZAT10- and GhCBF4-mediated freezing stress reactions in cotton, thereby establishing a foundation for further research on the molecular mechanisms underlying cotton freezing tolerance.

Exogenous Melatonin Positively Regulates Rice Root Growth through Promoting the Antioxidant System and Mediating the Auxin Signaling under Root-Zone Hypoxia Stress

Root growth and development is an important indicator of root-zone hypoxia tolerance in rice. Melatonin has been suggested to function as a crucial regulator in modulating root growth and improving plant abiotic stress resistance. To explore the role and potential mechanism of melatonin in regulating the root growth under root-zone hypoxia stress, rice seedlings were treated with hypoxia (oxygen level at 0.9–2.1 mg·L−1), combined with or without a 20 μmol·L−1 melatonin pretreatment under a hydroponic condition. The results showed that the exogenous application of melatonin significantly alleviated the inhibition of the rice root growth that was induced by the hypoxia stress. The morphological–phenotypic analyses showed that after the melatonin pretreatment, the primary root length, lateral root length, and lateral root density increased by 11.6%, 8.2%, and 36.8%, respectively, under hypoxia stress. The physiological–biochemical analyses showed that the exogenous melatonin significantly increased the root activity and O2 influx in the root meristem zone under hypoxia stress to 1.5 times that observed in the hypoxia stress group. The melatonin pretreatment significantly improved the activity of superoxide dismutase (SOD) and decreased the accumulation of superoxide anions (O2•−) in the seedling roots, whereas it increased the content of hydrogen peroxide (H2O2) under hypoxia stress. The exogenous melatonin pretreatment significantly increased the content of indole-3-acetic acid (IAA) by 51.5% in the rice roots compared to the plants without melatonin pretreatment under hypoxia stress. Quantitative real-time PCR (qRT-PCR) analyses revealed that the melatonin pretreatment induced the expression of OsPIN1a~1d, OsPIN8, OsPIN9, OsAUX1, OsARF19, and OsGH3-2 in the rice seedling roots under aerated conditions, whereas it only obviously upregulated the expression of OsPIN1b, OsPIN2, and OsGH3-2 under hypoxia stress. These results indicate that melatonin positively regulates root growth and development under hypoxia stress, through improving the antioxidant system and directly or indirectly activating the auxin signaling pathway. This study demonstrates the important role of melatonin to modulate root growth under hypoxia stress, providing a new strategy for improving hypoxia tolerance.

Exogenous Proline Improves Salt Tolerance of Alfalfa through Modulation of Antioxidant Capacity, Ion Homeostasis, and Proline Metabolism.

Alfalfa (Medicago sativa L.) is an important forage crop, and its productivity is severely affected by salt stress. Although proline is a compatible osmolyte that plays an important role in regulating plant abiotic stress resistance, the basic mechanism of proline requires further clarification regarding the effect of proline in mitigating the harmful effects of salinity. Here, we investigate the protective effects and regulatory mechanisms of proline on salt tolerance of alfalfa. The results show that exogenous proline obviously promotes seed germination and seedling growth of salt-stressed alfalfa. Salt stress results in stunted plant growth, while proline application alleviates this phenomenon by increasing photosynthetic capacity and antioxidant enzyme activities and decreasing cell membrane damage and reactive oxygen species (ROS) accumulation. Plants with proline treatment maintain a better K+/Na+ ratio by reducing Na+ accumulation and increasing K+ content under salt stress. Additionally, proline induces the expression of genes related to antioxidant biosynthesis (Cu/Zn-SOD and APX) and ion homeostasis (SOS1, HKT1, and NHX1) under salt stress conditions. Proline metabolism is mainly regulated by ornithine-δ-aminotransferase (OAT) and proline dehydrogenase (ProDH) activities and their transcription levels, with the proline-treated plants displaying an increase in proline content under salt stress. In addition, OAT activity in the ornithine (Orn) pathway rather than Δ1-pyrroline-5-carboxylate synthetase (P5CS) activity in the glutamate (Glu) pathway is strongly increased under salt stress, made evident by the sharp increase in the expression level of the OAT gene compared to P5CS1 and P5CS2. Our study provides new insight into how exogenous proline improves salt tolerance in plants and that it might be used as a significant practical strategy for cultivating salt-tolerant alfalfa.

Inhibition of UV-B stress in lettuce through enzyme-like Scutellaria baicalensis carbon dots

Oxidative stress in plants caused by UV-B stress has always been a great challenge to the yield of agricultural products. Carbon dots (CDs) with enzyme-like activity have been developed, and inhibiting oxidative stress in animals has been achieved, but little is known about abiotic stress resistance in plants, especially UV-B stress. In this study, CDs were synthesized from Scutellaria baicalensis via a hydrothermal method. The ability of CDs to scavenge reactive oxygen species (ROS) in vivo and in vitro and to enhance antioxidant resistance in vivo was evaluated. The results show that CDs promoted the nutrient assimilation ability of lettuce seedlings and protected the plants from UV-B stress by increasing the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glutathione reductase (GR), and ascorbate peroxidase (APX). Moreover, the antioxidant metabolism of plants can be activated by CDs and the expression levels of aquaporin (AQP) genes PIP1 and PIP2 are also up-regulated. These results facilitate the design and fabrication of CDs to meet the challenge of abiotic stress in food production.

An apple long-chain acyl-CoA synthase, MdLACS1, enhances biotic and abiotic stress resistance in plants

Epidermal waxes are part of the outermost hydrophobic structures of apples and play a significant role in enhancing apple resistance and improving fruit quality. The biosynthetic precursors of epidermal waxes are very long-chain fatty acids (VLCFAs), which are made into different wax components through various wax synthesis pathways. In Arabidopsis thaliana, the AtLACS1 protein can activate the alkane synthesis pathway to produce very long-chain acyl CoAs (VLC-acyl-CoAs), which provide substrates for wax synthesis, from VLCFAs. The apple protein MdLACS1, encoded by the MdLACS1 gene, belongs to the AMP-binding superfamily and has long-chain acyl coenzyme A synthase activity, but its function in apple remains unclear. Here, we identified MdLACS1 in apple (Malus × domestica) and analyzed its function. Our results suggest that MdLACS1 promotes wax synthesis and improves biotic and abiotic stress tolerance, which were directly or indirectly dependent on wax. Our study further refines the molecular mechanism of wax biosynthesis in apples and elucidates the physiological function of wax in resistance to external stresses. These findings provide candidate genes for the synergistic enhancement of apple fruit quality and stress tolerance.

Algal-Mediated Nanoparticles, Phycochar, and Biofertilizers for Mitigating Abiotic Stresses in Plants: A Review

The excessive use of agrochemicals to ensure food security under the conditions of a growing population, global climate change, weather extremes, droughts, wasteful use of freshwater resources, and land degradation has created severe challenges for sustainable crop production. Since the frequent and abrupt environmental changes are outcompeting the existing agricultural technologies of crop production systems to meet food security, the development and use of modern technologies and nature-based solutions are urgently needed. Nanotechnology has shown potential for revolutionizing agri-production and agri-business in terms of nanofertilizers and nanoparticles for crop protection. Furthermore, in the recent past, biochar has been identified as a negative emission technology for carbon sequestration and soil fertility improvement. However, supply chain issues for biochar, due to feedstock availability, challenges its worldwide use and acceptability. Meanwhile progress in algae research has indicated that, algae can be utilized for various agro-ecosystem services. Algae are considered an efficient biological species for producing biomass and phytochemicals because of their high photosynthetic efficiency and growth rate compared to terrestrial plants. In this context, various options for using algae as a nature-based solution have been investigated in this review; for instance, the possibilities of producing bulk algal biomass and algal-based biofertilizers and their role in nutrient availability and abiotic stress resistance in plants. The potential of algae for biochar production (hereafter “phycochar” because of algal feedstock), its elemental composition, and role in bioremediation is discussed. The potential role of agal nanoparticles’ in mitigating abiotic stress in crop plants was thoroughly investigated. This review has effectively investigated the existing literature and improved our understanding that, algae-based agro-solutions have huge potential for mitigating abiotic stresses and improving overall agricultural sustainability. However, a few challenges, such as microalgae production on a large scale and the green synthesis of nanoparticle methodologies, still need further mechanistic investigation.

Exogenous Proline Alleviated Low Temperature Stress in Maize Embryos by Optimizing Seed Germination, Inner Proline Metabolism, Respiratory Metabolism and a Hormone Regulation Mechanism

Proline (Pro) is not only an important osmotic adjustment substance, but it also plays an important role in regulating plant abiotic stress resistance. The maize varieties, Xinxin 2 (low temperature insensitive) and Damin 3307 (low temperature sensitive), were chosen as materials, setting a normal temperature for germination (22 °C/10 °C, 9d), low temperature germination (4 °C/4 °C, 5d) and normal temperature recovery (22 °C/10 °C, 4d), combined with a proline (15 mmol·L−1) soaking treatment, to reveal the seed germination and regulation mechanism in maize embryos. The results showed that proline significantly improved the germination potential, germination rate, germination index and vigor index of seeds under low temperature stress, increasing the length of the coleoptile and radicle, increasing the dry and fresh weight of young buds (coleoptile + radicle), and increasing the activity of α-amylase. Proline enhanced the activities of Δ1-pyrroline-5-carboxylic acid synthetase (P5CS) and ornithine aminotransferase (OAT) in maize embryos under low temperature stress, enhanced the proline synthesis pathways, and further enhanced proline accumulation. Proline induced the activity of proline dehydrogenase (ProDH) in the early stage of low temperature stress and stress relief. Under low temperature stress, the activities of hexokinase (HXK), phosphofructokinase (PFK), pyruvate kinase (PK), isocitrate dehydrogenase (IDH), succinate dehydrogenase (SDH), malate dehydrogenase (MDH) and glucose-6-phosphate dehydrogenase (G-6-PDH) and glucose-6-phosphate dehydrogenase (G-6-PDH and 6-P-GDH) in maize embryos were decreased, resulting in a decrease in the glycolysis (EMP) pathway, tricarboxylic acid (TCA) cycle and pentose phosphate pathway (PPP). Proline alleviated the inhibition of key enzyme activities of the EMP pathway, TCA cycle and PPP of maize embryos under low temperature stress, increased the activities of cytochrome oxidase (COX) and alternative oxidase (AOX), increased the ATP content, alleviated the inhibition of low temperature stress on main cytochrome pathway activity (ρVcyt), while further increasing the total respiratory activity (Vt) and the actual operational activity of the alternative pathway (ρValt) during seed germination at the initial stage of low temperature stress, as well as improving the inhibition of the Vt and ρValt in the middle and late stages of low temperature stress. Under low temperature stress, the content of abscisic acid (ABA) increased significantly, while gibberellin (GA), auxin (IAA) and zeatin nucleoside (ZR) decreased significantly. Proline alleviated the decrease in IAA, ZR and GA contents in maize embryos under low temperature stress, reduced the increase in the ABA content, and reduced the inhibition of low temperature on seed germination.

Identification and functional characterization of a cystathionine β-lyase (CBL) enzyme for H2S production in Arabidopsis thaliana

Sulfide or sulfur metabolism plays an important role in the growth and development of plants. Cystathionine β-lyase (CBL) is an important enzyme in methionine synthesis, but a comprehensive understanding of CBL functions is limited. As the third gasotransmitter, hydrogen sulfide (H2S) plays important physiological roles in plants. In this study, we found that the endogenous H2S content in Arabidopsis thaliana cbl mutants was lower than that in the wild type. Under PEG-based osmotic stress conditions, the H2S contents of CBL-overexpression (OE-CBL) plants increased significantly compared with the wild type. Additionally, the OE-CBL plants increased their tolerance to osmotic stress by increasing the transcription levels of drought-related genes and their relative water-loss rates. Compared with cbl and wild type, OE-CBL plants resisted drought stress by significantly closing their stomata, resulting in improved survival rates. Root tip-bending experiments showed that CBL overexpression relieved osmotic, heavy metal and cold stresses in Arabidopsis. The recombinant CBL activity in vitro revealed that CBL produced H2S using L-cysteine as a substrate. Thus, CBL had a very strong cysteine desulfhydrase activity that could produce endogenous H2S using L-cysteine as a substrate, and it played an important role in plant abiotic stress resistance.

Genome-Wide Identification and Analysis of bZIP Gene Family and Resistance of TaABI5 (TabZIP96) under Freezing Stress in Wheat (Triticum aestivum).

The basic leucine zipper (bZIP) regulates plant growth and responds to stress as a key transcription factor of the Abscisic acid (ABA) signaling pathway. In this study, TabZIP genes were identified in wheat and the gene structure, physicochemical properties, cis-acting elements, and gene collinearity were analyzed. RNA-Seq and qRT-PCR analysis showed that ABA and abiotic stress induced most TabZIP genes expression. The ectopic expression of TaABI5 up-regulated the expression of several cold-responsive genes in Arabidopsis. Physiological indexes of seedlings of different lines under freezing stress showed that TaABI5 enhanced the freezing tolerance of plants. Subcellular localization showed that TaABI5 is localized in the nucleus. Furthermore, TaABI5 physically interacted with cold-resistant transcription factor TaICE1 in yeast two-hybrid system. In conclusion, this study identified and analyzed members of the TabZIP gene family in wheat. It proved for the first time that the gene TaABI5 affected the cold tolerance of transgenic plants and was convenient for us to understand the cold resistance molecular mechanism of TaABI5. These results will provide a new inspiration for further study on improving plant abiotic stress resistance.

Role of Glycine Betaine in the Thermotolerance of Plants

As global warming progresses, agriculture will likely be impacted enormously by the increasing heat stress (HS). Hence, future crops, especially in the southern Mediterranean regions, need thermotolerance to maintain global food security. In this regard, plant scientists are searching for solutions to tackle the yield-declining impacts of HS on crop plants. Glycine betaine (GB) has received considerable attention due to its multiple roles in imparting plant abiotic stress resistance, including to high temperature. Several studies have reported GB as a key osmoprotectant in mediating several plant responses to HS, including growth, protein modifications, photosynthesis, gene expression, and oxidative defense. GB accumulation in plants under HS differs; therefore, engineering genes for GB accumulation in non-accumulating plants is a key strategy for improving HS tolerance. Exogenous application of GB has shown promise for managing HS in plants, suggesting its involvement in protecting plant cells. Even though overexpressing GB in transgenics or exogenously applying it to plants induces tolerance to HS, this phenomenon needs to be unraveled under natural field conditions to design breeding programs and generate highly thermotolerant crops. This review summarizes the current knowledge on GB involvement in plant thermotolerance and discusses knowledge gaps and future research directions for enhancing thermotolerance in economically important crop plants.

NRT1.1 Dual-Affinity Nitrate Transport/Signalling and its Roles in Plant Abiotic Stress Resistance.

NRT1.1 is the first nitrate transport protein cloned in plants and has both high- and low-affinity functions. It imports and senses nitrate, which is modulated by the phosphorylation on Thr101 (T101). Structural studies have revealed that the phosphorylation of T101 either induces dimer decoupling or increases structural flexibility within the membrane, thereby switching the NRT1.1 protein from a low- to high-affinity state. Further studies on the adaptive regulation of NRT1.1 in fluctuating nitrate conditions have shown that, at low nitrate concentrations, nitrate binding only at the high-affinity monomer initiates NRT1.1 dimer decoupling and priming of the T101 site for phosphorylation activated by CIPK23, which functions as a high-affinity nitrate transceptor. However, nitrate binding in both monomers retains the unmodified NRT1.1, maintaining the low-affinity mode. This NRT1.1-mediated nitrate signalling and transport may provide a key to improving the efficiency of plant nitrogen use. However, recent studies have revealed that NRT1.1 is extensively involved in plant tolerance of several adverse environmental conditions. In this context, we summarise the recent progress in the molecular mechanisms of NRT1.1 dual-affinity nitrate transport/signalling and focus on its expected and unexpected roles in plant abiotic stress resistance and their regulation processes.

Vacuolar membrane H+-ATPase cˋˋ subunit gene (ThVHAcˋˋ1) from Tamarix hispida Willd improves salt stress tolerance

The plant vacuolar H+-ATPase (V-ATPase) is a multisubunit complex. In addition to performing basic housekeeping functions, this complex is also involved in abiotic stress resistance in plants. In this study, a V-ATPase cˋˋ subunit gene (ThVHAcˋˋ1) from Tamarix hispida Willd was cloned with a 534-bp ORF. Sequence analysis showed that the ThVHAcˋˋ1 protein contains four transmembrane helices and lacks a signal peptide. qRT-PCR results showed that ThVHAcˋˋ1 was primarily induced by treatments of NaCl, NaHCO3, PEG6000, CdCl2 or ABA in roots, stems and leaves of T. hispida. The expression pattern of ThVHAcˋˋ1 was significantly different from that of ThVHAc1 (a V-ATPase c subunit in T. hispida). Furthermore, the cell survival rates and density (OD600) results showed that the transgenic yeast overexpressing ThVHAcˋˋ1 exhibited increased tolerance to the above-mentioned abiotic stresses. In addition, the overexpression of ThVHAcˋˋ1 confers salt tolerance to transgenic Arabidopsis plants by improving the ROS content and decreasing the accumulation of O2− and H2O2. Similarly, the homologous transformation of the ThVHAcˋˋ1 gene into T. hispida also improved salt tolerance. Our results suggest that the ThVHAcˋˋ1 gene plays an important role in plant stress tolerance.

Effects of exopolysaccharide derived from Pantoea alhagi NX-11 on drought resistance of rice and its efficient fermentation preparation

Exopolysaccharide (EPS) plays an important role in plant growth-promoting bacteria (PGPB)-mediated enhancement of plant abiotic stress resistance. In this study, it is found that EPS from Pantoea alhagi NX-11 foliar sprayed at 20, 50, and 100 ppm could significantly enhance drought resistance of rice seedlings. The fresh weight and relative water content of EPS sprayed were increased. In addition, malondialdehyde content reduced while total chlorophyll, proline and soluble sugar content, prominent enhanced. Meanwhile, the antioxidant enzymes, CAT, POD and SOD, were also significantly increased. The drought resistance of rice was most pronounced at the 50 ppm EPS dose. For the sake of commercializing the gram-negative EPS-producing PGPB which were difficult to preserve, it is vital to improve the EPS yield. First, the carbon source, nitrogen source and inorganic salt were optimized. Subsequently, the effect of three oxygen vectors, which could increase the efficiency of oxygen mass transfer, on EPS yield was studied by response surface methodology. The maximum EPS yield (19.27 g/L) was obtained, which is 51.7% higher than the initial yield of 12.7 g/L. Overall, it may provide a new way for the industrialization of PGPB to increase the yield of EPS.

The Calcium Sensor CBL2 and Its Interacting Kinase CIPK6 Are Involved in Plant Sugar Homeostasis via Interacting with Tonoplast Sugar Transporter TST2.

Calcineurin B-like protein (CBL) and CBL-interacting protein kinase (CIPK)-mediated calcium signaling has been widely reported to function in plant development and various stress responses, particularly in ion homeostasis. Sugars are the most important primary metabolites, and thus sugar homeostasis requires precise regulation. Here, we describe a CBL2-CIPK6-Tonoplast-Localized Sugar Transporter2 (TST2) molecular module in cotton (Gossypium hirsutum) that regulates plant sugar homeostasis, in particular Glc homeostasis. GhCIPK6 is recruited to the tonoplast by GhCBL2 and interacts with the tonoplast-localized sugar transporter GhTST2. Overexpression of either GhCBL2, GhCIPK6, or GhTST2 was sufficient to promote sugar accumulation in transgenic cotton, whereas RNAi-mediated knockdown of GhCIPK6 expression or CRISPR-Cas9-mediated knockout of GhTST2 resulted in significantly decreased Glc content. Moreover, mutation of GhCBL2 or GhTST2 in GhCIPK6-overexpressing cotton reinstated sugar contents comparable to wild-type plants. Heterologous expression of GhCIPK6 in Arabidopsis (Arabidopsis thaliana) also promoted Glc accumulation, whereas mutation of AtTST1/2 in GhCIPK6-overexpressing Arabidopsis similarly reinstated wild-type sugar contents, thus indicating conservation of CBL2-CIPK6-TST2-mediated sugar homeostasis among different plant species. Our characterization of the molecular players behind plant sugar homeostasis may be exploited to improve sugar contents and abiotic stress resistance in plants.

Bacillus subtilis strain GOT9 confers enhanced tolerance to drought and salt stresses in Arabidopsis thaliana and Brassica campestris

Soil is a primary source of water and inorganic nutrients vital for plant growth. In particular, the rhizosphere, a microecological region around the plant roots, is enriched with root exudates that enable beneficial microbial communities to form. Plant growth-promoting rhizobacteria (PGPR) are rhizosphere bacteria that contribute to the improvement of plant growth through diverse physiological mechanisms. Identifying PGPR is beneficial for agriculture because their use can effectively increase the productivity of plants without the harmful side effects of chemical fertilizers. To further enrich the pool of PGPR that contribute to abiotic stress resistance in plants, we screened roughly 491 bacteria that had previously been isolated in soil from Gotjawal in Jeju island, South Korea. Among several candidates, the application of Bacillus subtilis strain GOT9, led to the enhancement of drought and salt stress tolerance in Arabidopsis. In agreement with the increased stress tolerance phenotypes, its application resulted in increases in the transcripts of various drought stress- and salt stress-inducible genes in the absence or presence of the stresses. Furthermore, the treatment resulted in improved lateral root growth and development in Arabidopsis. GOT9 also led to enhanced tolerance against drought and salt stresses and to upregulation of drought-inducible genes in Brassica, a closely related crop to Arabidopsis. Taken together, these results show that GOT9 could be utilized as a biotic resource that effectively minimizes damage to plants from environmental stresses.