Mechanisms of plant saline-alkaline tolerance

Cultivar-specific rhizosphere microbial community responses to cadmium-NaHCO3 stress in relation to cadmium accumulation in rice

Understanding the response of rhizosphere microbial communities to cadmium (Cd)-alkali stress from a cultivar-specific perspective is important for regulating Cd accumulation in rice. Pot experiments were conducted using low-Cd-accumulating Y15 and high-Cd-accumulating Y40, by addition of 0.0 %, 0.3 %, and 0.6 % NaHCO3 (A0, A1, and A2, respectively) to Cd-contaminated (0.62 mg/kg) soil. The plant Cd and soil DTPA-Cd decreased significantly with increasing NaHCO3 dose for Y15, but not for Y40. Cd-NaHCO3 stress reduced the richness and evenness of rhizosphere microbial communities, especially in A1 of Y15 and A2 of Y40. The Y15 rhizosphere shifted from the equal abundance of Proteobacteria and Firmicutes under A0 to the predominance of Proteobacteria and enriched with growth-promoting Alphaproteobacteria (Roseomonas, Brevundimonas), Cd-fixating Firmicute (Bacillus), and nitrogen-cycling Bdellovibrionota (Peredibacter) under A1 and A2. The Y40 rhizosphere contained comparable Proteobacteria and Firmicutes under A0 and A1; under A2, it was dominated by Proteobacteria and enriched with Cd-activating Bacteroidota (Barnesiella, Taibaiella), lignin-degrading Chloroflexi (Anaerolinea), and Cd-fixating or growth-promoting Gammaproteobacteria (Lysobacter, Pseudomonadales, Acinetobacter). The Y40 and Y15 rhizosphere exhibited laziness in multiple FAPROTAX functions, and were activated in 11 and 18 KGEE pathways including amino acid metabolism in A2 and A1, respectively. The results provide new insights into Cd-alkali tolerance in rice.

A large-scale gene co-expression network analysis reveals Glutamate Dehydrogenase 2 (GhGDH2_D03) as a hub regulator of salt and salt-alkali tolerance in cotton

Salt stress and salt-alkali stress significantly inhibit the normal growth and development of plants. Understanding the molecular mechanisms of cotton responses to these stresses is crucial for improve yield and fiber quality. In this study, we conducted a comprehensive analysis of the transcriptome dynamics under salt and salt-alkali stress conditions, utilizing 234 RNA-seq datasets compiled from 11 previous studies. After systematic evaluation and correction for batch effects, we observed that root transcriptomes clustered more consistently than leaf transcriptomes across stress treatment and time points. Weighted gene co-expression network analysis (WGCNA) on 123 root transcriptomes identified three key modules, with their hub genes significantly associated with salt and salt-alkali tolerance. Virus-induced gene silencing assay and RNA-seq analysis indicated that GhGDH2_D03 (Gohir.D03G104800), a module hub gene encoding Glutamate Dehydrogenase 2, positively regulates salt and salt-alkali tolerance in cotton by modulating multiple signaling pathways and metabolic processes, including the ethylene signaling pathway. This study underscores the pivotal role of GhGDH2_D03 in conferring tolerance to salt and salt-alkali stress, in addition to its previous reported involvement in biotic stress defense, providing valuable insights and genetic resources for cotton breeding.

Micro/Nanoplastics in plantation agricultural products: behavior process, phytotoxicity under biotic and abiotic stresses, and controlling strategies

With the extensive utilization of plastic products, microplastics/nanoplastics (MPs/NPs) contamination not only poses a global hazard to the environment, but also induces a new threat to the growth development and nutritional quality of plantation agricultural products. This study thoroughly examines the behavior of MPs/NPs, including their sources, entry routes into plants, phytotoxicity under various biotic and abiotic stresses (e.g., salinity, polycyclic aromatic hydrocarbons, heavy metals, antibiotics, plasticizers, nano oxide, naturally occurring organic macromolecular compounds, invasive plants, Botrytis cinerea mycorrhizal fungi.) and controlling strategies. MPs/NPs in agricultural systems mainly originate from mulch, sewage, compost fertilizer, municipal solid waste, pesticide packaging materials, etc. They enter plants through endocytosis, apoplast pathways, crack-entry modes, and leaf stomata, affecting phenotypic, metabolic, enzymatic, and genetic processes such as seed germination, growth metabolism, photosynthesis, oxidative stress and antioxidant defenses, fruit yield and nutrient quality, cytotoxicity and genotoxicity. MPs/NPs can also interact with other environmental stressors, resulting in synergistic, antagonistic, or neutral effects on phytotoxicity. To address these challenges, this review highlights strategies to mitigate MPs/NPs toxicity, including the development of novel green biodegradable plastics, plant extraction and immobilization, exogenous plant growth regulator interventions, porous nanomaterial modulation, biocatalysis and enzymatic degradation. Finally, the study identifies current limitations and future research directions in this critical field.

Multiple functions of exogenous melatonin in cucumber seed germination, seedling establishment, and alkali stress resistance

BACKGROUND

Exogenous melatonin plays a crucial role in various plant developmental processes and stress responses and has considerable potential for future agricultural applications. However, its effects on early cucumber seedling growth and resistance to alkaline stress have not been adequately explored. This study investigated the role of exogenous melatonin during the early growth stages of cucumber, specifically focusing on seed germination, post-germination seedling growth, and 1-leaf stage seedling growth, with particular emphasis on its influence on alkali stress resistance. These findings are intended to enhance the application of melatonin in cucumber seedling cultivation and provide a theoretical basis for promoting growth and improving stress tolerance in agricultural production.

RESULTS

Exogenous melatonin enhanced cucumber seed germination and early seedling growth with promoting and inhibitory effects at low and high concentrations, respectively. However, the effects of exogenous melatonin on cucumber growth varied at different developmental stages. Additionally, alkali stress significantly hampered the growth of cucumber seedlings; however, the external application of melatonin mitigated the damage caused by this stress. This protective effect was evidenced by a marked increase in the survival rate, stem diameter, and biomass of cucumber seedlings, along with a significant reduction in malondialdehyde content and electrolyte leakage rate. Further investigation revealed that exogenous melatonin promotes the accumulation of osmoregulatory substances, specifically soluble sugars, and proline, under alkaline stress. It also enhances the activities of antioxidant enzymes, including peroxidase, superoxide dismutase, catalase, and dehydroascorbate reductase, while significantly decreasing the accumulation of reactive oxygen species such as H2O2 and O2⋅-. Furthermore, exogenous melatonin increased the activities of PM-H+-ATPase and V-H+-ATPase and stimulated the expression of stress-related genes, thereby regulating Na+ and K+ homeostasis under alkali stress. Additionally, exogenous melatonin promoted the synthesis of endogenous melatonin in cucumbers subjected to alkaline stress by inducing the expression of melatonin synthase genes, namely, CsASMT, CsCOMT, CsTDC, and CsSNAT.

CONCLUSIONS

Exogenous melatonin promoted cucumber seed germination and seedling establishment and enhanced cucumber alkali stress tolerance by mediating osmotic adjustment, reactive oxygen species scavenging, ion homeostasis maintenance, endogenous melatonin synthesis, and expression of stress-related genes.

Differences in growth, ionomic and antioxidative enzymes system responded to neutral and alkali salt exposure in halophyte Haloxylon ammodendron seedlings

Soil salinity and alkalinity severely suppress plant growth and crop yields. This study compared the effects of neutral and alkaline salt exposure, both individually and mixed, on metal content and morphophysiological responses in halophyte Haloxylon ammodendron. Our results showed that alkaline salt exposure more considerably inhibited the growth and photosynthesis of H. ammodendron than neutral salt exposure. Under neutral salt conditions, Na accumulated significantly, while K and Fe absorption was hindered. In contrast, under alkaline salt stress, Na accumulation was more pronounced, leading to a greater inhibition of K absorption. Additionally, Ca accumulation was promoted, while the transport of Fe, Mg, and Cu from root to shoot was suppressed. Alkaline salt stress also induced more severe osmotic stress, triggering a stronger accumulation of soluble sugars to counteract it. Furthermore, seedlings under alkaline stress showed higher levels of REL, H2O2, and MDA, but lower activities of SOD, POD, CAT, and APX, indicating increased oxidative damage. These findings suggest that H. ammodendron can adapt well to neutral salt stress through efficient antioxidant enzyme systems and osmotic stress regulation. In contrast, alkaline stress severely inhibits the absorption and transport of mineral elements and disrupts the balance of antioxidant enzymes. Besides, the deleterious effects of neutral-alkaline salt mixed stress were significantly less than those of alkaline stress alone, indicating a reciprocal enhancement between neutral and alkaline salt stress was occurred.

Microbial functional genes play crucial roles in enhancing soil nutrient availability of halophyte rhizospheres in salinized grasslands

Land degradation due to salinization threatens ecosystem health. Phytoremediation, facilitated by functional microorganisms, has gained attention for improving saline-alkali soils. However, the relationship between the functional potential of rhizosphere microbes involved in multi-element cycling and soil nutrient pools remain unclear. This study focused on the changes in functional genes related to carbon (C), nitrogen (N), and phosphorus (P) cycling in the rhizospheres of various halophytes and bulk soil in the grassland ecosystem of Chaka Salt Lake, Qinghai Province, China. Our evaluation of plant and soil characteristics revealed that halophyte growth increased soil hydrolase activity and nutrient levels, particularly available N. Significant differences were observed in foliage and root nutrients, rhizosphere soil properties, and microbial functional gene composition among plant species. Halophytes significantly altered the abundance of genes involved in C fixation (Calvin and DC/4-HB cycles), C degradation (starch, hemicellulose, cellulose, and pectin degradation), dissimilatory nitrate reduction (nirB), ammonification (ureC), organic P mineralization (phoA and ugpQ), P transport (phnE), and inorganic P dissolution (ppk1). C, N, and P cycling processes were closely related to soil N nutrients, available nutrient ratios, and C/N-cycling enzyme activities. Partial least squares path modeling (PLS-PM) analysis showed that microbial functional genes were directly associated with soil nutrient availability, with soil and plant variables indirectly affecting nutrient pools through the regulation of these genes. These findings enhance our understanding of the biochemical cycling in halophyte rhizospheres and highlight the role of microbial functional genes in saline-alkali soil restoration.

Brassinosteroid Enhances Cucumber Stress Tolerance to NaHCO3 by Modulating Nitrogen Metabolism, Ionic Balance and Phytohormonal Response

Under NaHCO3 stress, exogenous 24-epibrassinolide (EBR) markedly alleviated Na+ accumulation in cucumber plants, thereby decreasing the Na+/K+, Na+/Mg2+, and Na+/Ca2+ ratios. This mitigation was accompanied by elevated concentrations of K+, Ca2+, and Mg2+, as well as enhanced expression of the NHX and SOS1 genes. In addition, the activities of plasma membrane H+-ATPase, vesicular membrane H+-ATPase, and vesicular membrane H+-PPase were significantly increased, contributing to the maintenance of ionic balance in cucumber plants. NaHCO3 stress disrupted nitrogen metabolism, as evidenced by reductions in the activities of NR, GS, GOGAT, GOT, and GPT, along with altered GDH activity. These disruptions led to an accumulation of NH4+ and substantial decreases in NO3--N and total nitrogen content. Exogenous EBR alleviated these effects by enhancing the activities of NR, GS, GOGAT, GOT, and GPT, countering the prolonged suppression of GDH activity, and restoring NO3--N and total nitrogen levels. Consequently, EBR application reduced NH4+ toxicity induced by alkali stress. Additionally, NaHCO3 stress increased ABA accumulation while decreasing IAA and GA3 content in cucumber seedlings. In contrast, exogenous EBR application elevated IAA and GA3 levels and increased the IAA/ABA and GA3/ABA ratios, thus maintaining hormonal equilibrium under alkali stress. Collectively, these findings highlight that exogenous EBR enhances the alkaline tolerance of cucumber plants by regulating nitrogen metabolism, ion homeostasis, and phytohormonal responses.

The Impact of Alkaline Stress on Plant Growth and Its Alkaline Resistance Mechanisms

Alkaline stress can induce significant injury to plants, resulting in a range of negative effects, including ion toxicity, oxidative stress, and damage from high pH values. These stress factors can substantially affect normal plant growth and development, as well as yield and quality loss. To counteract alkaline stress, plants have developed a range of defense strategies, enabling them to adapt and thrive in challenging environments. These defense mechanisms operate at multiple levels such as morphological, physiological, biochemical, and molecular. The continuous advancement of genetic engineering has enabled significant breakthroughs in enhancing plant alkali resistance through human intervention. This research provides a scientific basis for crop production and ecological environment construction, and also promotes the effective development and utilization of saline-alkali lands, improving the sustainability of agricultural production.

Insights into the Heat Shock Protein 70 (Hsp70) Family in Camelina sativa and Its Roles in Response to Salt Stress

Hsp70s, a group of heat shock proteins, are ancient proteins that play a crucial part in maintaining the stability of cells when faced with various internal and external stresses. In this research, there are 72 CsHSP70 genes present and verified in Camelina sativa, all of which exhibit a wide range of physicochemical characteristics. Through evolutionary analysis, the Hsp70 family was categorized into five primary groups, and numerous segmental duplications were anticipated among the CsHSP70 genes. The GO enrichment analysis of co-expression network elements revealed a significant association between key signaling terms, such as phosphorelay signal transduction, and MAPK cascade with the function of CsHsp70. An analysis of transcriptome data exposed to cold, drought, salinity, and cadmium stress demonstrated the varied expression profiles of CsHsp70 genes. The expression levels of CsHSP70 genes varied across various organs and stages of development in camelina, although some of them illustrated tissue-specific expression. qRT-PCR analysis further disclosed that CsHsp70-60, -52, and -13 were up-regulated and CsHsp70-03, -58, and -09 showed down-regulation in response to salinity. Furthermore, CsHsp70 genes are categorized as late-responsive elements to salinity stress. Through docking analysis, the current research revealed that CsHsp70 proteins interacted with ABA, BR, and MeJA.

C2-domain abscisic acid-related proteins regulate the dynamics of a plasma membrane H+-ATPase in response to alkali stress

Arabidopsis (Arabidopsis thaliana) H+-ATPase1 (AHA1), a plasma membrane (PM)-localized H+-ATPase, plays a key role in plant alkali stress tolerance by pumping protons from the cytoplasm to the apoplast. However, its molecular dynamics are poorly understood. We report that many C2-domain ABA-related (CAR) protein family members interact with AHA1 in Arabidopsis. Single or double mutants of CAR1, CAR6, and CAR10 had no obvious phenotype of alkali stress tolerance, while their triple mutants showed significantly higher tolerance to this stress. The disruption of AHA1 largely compromised the increased alkali stress tolerance of the car1car6car10 mutant, revealing a key role of CARs in AHA1 regulation during the plant's response to a high alkali pH. Furthermore, variable-angle total internal reflection fluorescence microscopy was used to observe AHA1-mGFP5 in intact Arabidopsis seedlings, revealing the presence of heterogeneous diffusion coefficients and oligomerization states in the AHA1 spots. In the aha1 complementation lines, alkali stress curtailed the residence time of AHA1 at the PM and increased the diffusion coefficient and particle velocity of AHA1. In contrast, the absence of CAR proteins decreased the restriction of the dynamic behavior of AHA1. Our results suggest that CARs play a negative role in plant alkali stress tolerance by interacting with AHA1 and provide a perspective to investigate the regulatory mechanism of PM H+-ATPase activity at the single-particle level.

Participation of the stress-responsive CDSP32 thioredoxin in the modulation of chloroplast ATP-synthase activity in Solanum tuberosum

Plant thioredoxins (TRXs) are involved in numerous metabolic and signalling pathways, such as light-dependent regulation of photosynthesis. The atypical TRX CDSP32, chloroplastic drought-induced stress protein of 32 kDa, includes two TRX-fold domains and participates in responses to oxidative stress as an electron donor to other thiol reductases. Here, we further characterised potato lines modified for CDSP32 expression to clarify the physiological roles of the TRX. Upon high salt treatments, modified lines displayed changes in the abundance and redox status of CDSP32 antioxidant partners, and exhibited sensitivity to combined saline-alkaline stress. In non-stressed plants overexpressing CDSP32, a lower abundance of photosystem II subunits and ATP-synthase γ subunit was noticed. The CDSP32 co-suppressed line showed altered chlorophyll a fluorescence induction and impaired regulation of the transthylakoid membrane potential during dark/light and light/dark transitions. These data, in agreement with the previously reported interaction between CDSP32 and ATP-synthase γ subunit, suggest that CDSP32 affects the redox regulation of ATP-synthase activity. Consistently, modelling of protein complex 3-D structure indicates that CDSP32 could constitute a suitable partner of ATP-synthase γ subunit. We discuss the roles of the TRX in the regulation of both photosynthetic activity and enzymatic antioxidant network in relation with environmental conditions.

Alkaline tolerance in plants: The AT1 gene and beyond

Salt stress poses a serious challenge to crop production and a significant threat to global food security and ecosystem sustainability. Soil salinization commonly occurs in conjunction with alkalization, which causes combined saline-alkaline stress. Alkaline soil predominantly comprises NaHCO3 and Na2CO3 and is characterized by a high pH. The combined saline-alkaline stress is more harmful to crop production than neutral salt stress owing to the effects of both elevated salinity and high pH stress. Through genome association analysis of sorghum, a recent study has identified Alkaline tolerance 1 (AT1) as a contributor to alkaline sensitivity in crops. AT1, which is the first gene to be identified as being specifically associated with alkaline tolerance, encodes a G protein γ-subunit (Gγ). Editing of AT1 enhances the yields of sorghum, rice, maize, and millet grown in alkaline soils, indicating that AT1 has potential for generating alkaline-resistant crops. In this review, we summarize the role of AT1 in alkaline tolerance in plants and present a phylogenetic analysis along with a motif comparison of Gγ subunits of monocot and dicot plants across various species.

Exploring genetics and genomics trends to understand the link between secondary metabolic genes and agronomic traits in cereals under stress

The plant metabolome is considered an important interface between the genome and its phenome, where it plays a significant role in regulating plant growth in response to various environmental cues. A wide array of specialized metabolites is produced by plants, which are essential for mediating environmental interactions and their adaptation. Notably, enhanced accumulation of these specialized metabolites, particularly plant secondary metabolites (PSMs), is a part of the chemical defense response that is directly linked to improved stress tolerance. Therefore, exploring the genetic diversity underlying the immense variation of the secondary metabolite pool could unravel the adaptation mechanisms in plants against different environmental stresses. The post-genomic profiling platforms have enabled the exploration of the link between metabolic diversity and important agronomic traits. The current review focuses on the major achievements and future challenges associated with plant secondary metabolite (PSM) research in graminaceous crops using advanced omics approaches. Given this, we briefly summarize different strategies adopted to explore the genetic diversity and evolution of PSMs in cereal crops. Further, we have discussed the recent technological advancements to integrate multi-omics approaches linking the metabolome diversity with the genome, transcriptome, and proteome of these crops under stress. Combining these data with phenomics (the omics of phenotypes) provides a holistic view of how plants respond to stress. Next, we outlined the genetic manipulation studies performed so far in cereals to engineer secondary metabolic pathways for enhanced stress tolerance. In summary, our review provides new insight into developing genetic and genomic trends in exploring the secondary metabolite diversity in graminaceous crops and discusses how this information can be utilized in designing strategies to generate future stress-resilient crops.

Evaluation of the microbial community in various saline alkaline-soils driven by soil factors of the Hetao Plain, Inner Mongolia

Soil microbial communities play a crucial role in maintaining diverse ecosystem functions within the saline-alkali soil ecosystems. Therefore, in this study, we collected various saline-alkaline soils from across the Inner Mongolia Hetao irrigation area. The soil chemical properties were analyzed, and the microbial diversity of bacteria and fungi was measured using 16 S rRNA and ITS rRNA amplicon sequencing. The dynamic relationship between the soil microbial community and soil factors was analyzed using the ABT (Aggregate Enhanced tree) model, the co-occurrence network, and the structural equation model. The results indicated that electrical conductivity (EC) was the biggest driving force of various saline-alkaline soils, affecting the community structure of bacteria (22.80%) and fungi (21.30%). The soil samples were categorized into three treatment levels based on their EC values: the low-salinity group (L, EC: 0-1 ms/cm, n = 10), the medium-salinity group (M, EC: 1-2 ms/cm, n = 8), and the high-salinity group (H, EC > 2 ms/cm, n = 6). The results demonstrated a negative correlation between microbial abundance and salinity-alkalinity, while revealing an enhanced interrelationship among species. The alterations in bacterial (12.36%) and fungal (22.92%) communities in various saline-alkali soils were primarily driven by saline-alkali ions, which served as the principal direct factors. The negative correlation between EC and SOM exhibited the highest magnitude, whereas the positive correlation between soil organic carbon and EC demonstrated the greatest strength. Therefore, it was further substantiated that EC played a pivotal role in shaping the distinct microbial communities in saline-alkali soils.

Promoting γ-aminobutyric acid accumulation to enhances saline-alkali tolerance in tomato

Saline-alkali stress is a widely distributed abiotic stress that severely limits plant growth. γ-Aminobutyric acid (GABA) accumulates rapidly in plants under saline-alkali stress, but the underlying molecular mechanisms and associated regulatory networks remain unclear. Here, we report a MYB-like protein, I-box binding factor (SlMYBI), which positively regulates saline-alkali tolerance through induced GABA accumulation by directly modulating the glutamate decarboxylase (GAD) gene SlGAD1 in tomato (Solanum lycopersicum L.). Overexpression of SlGAD1 increased GABA levels and decreased reactive oxygen species accumulation under saline-alkali stress, while silencing of SlGAD1 further suggested that SlGAD1 plays an active role in GABA synthesis and saline-alkali tolerance of tomato. In addition, we found that SlMYBI activates SlGAD1 transcription. Both overexpression of SlMYBI and editing of SlMYBI using CRISPR-Cas9 showed that SlMYBI regulates GABA synthesis by modulating SlGAD1 expression. Furthermore, the interaction of SlNF-YC1 with SlMYBI enhanced the transcriptional activity of SlMYBI on SlGAD1 to further improve saline-alkali tolerance in tomato. Interestingly, we found that ethylene signaling was involved in the GABA response to saline-alkali stress by RNA-seq analysis of SlGAD1-overexpressing lines. This study elucidates the involvement of SlMYBI in GABA synthesis regulation. Specifically, the SlMYBI-SlNF-YC1 module is involved in GABA accumulation in response to saline-alkali stress.

Challenges to rhizobial adaptability in a changing climate: Genetic engineering solutions for stress tolerance

Rhizobia interact with leguminous plants in the soil to form nitrogen fixing nodules in which rhizobia and plant cells coexist. Although there are emerging studies on rhizobium-associated nitrogen fixation in cereals, the legume-rhizobium interaction is more well-studied and usually serves as the model to study rhizobium-mediated nitrogen fixation in plants. Rhizobia play a crucial role in the nitrogen cycle in many ecosystems. However, rhizobia are highly sensitive to variations in soil conditions and physicochemical properties (i.e. moisture, temperature, salinity, pH, and oxygen availability). Such variations directly caused by global climate change are challenging the adaptive capabilities of rhizobia in both natural and agricultural environments. Although a few studies have identified rhizobial genes that confer adaptation to different environmental conditions, the genetic basis of rhizobial stress tolerance remains poorly understood. In this review, we highlight the importance of improving the survival of rhizobia in soil to enhance their symbiosis with plants, which can increase crop yields and facilitate the establishment of sustainable agricultural systems. To achieve this goal, we summarize the key challenges imposed by global climate change on rhizobium-plant symbiosis and collate current knowledge of stress tolerance-related genes and pathways in rhizobia. And finally, we present the latest genetic engineering approaches, such as synthetic biology, implemented to improve the adaptability of rhizobia to changing environmental conditions.

Analysis of Ion Transport Properties of Glycine max HKT Transporters and Identifying a Regulation of GmHKT1;1 by the Non-Functional GmHKT1;4

High-affinity potassium transporters (HKTs) play an important role in plants responding to salt stress, but the transport properties of the soybean HKT transporters at the molecular level are still unclear. Here, using Xenopus oocyte as a heterologous expression system and two-electrode voltage-clamp technique, we identified four HKT transporters, GmHKT1;1, GmHKT1;2, GmHKT1;3 and GmHKT1;4, all of which belong to type I subfamily, but have distinct ion transport properties. While GmHKT1;1, GmHKT1;2 and GmHKT1;3 function as Na+ transporters, GmHKT1;1 is less selective against K+ than the two other transporters. Astonishingly, GmHKT1;4, which lacks transmembrane segments and has no ion permeability, is significantly expressed, and its gene expression pattern is different from the other three GmHKTs under salt stress. Interestingly, GmHKT1;4 reduced the Na+/K+ currents mediated by GmHKT1;1. Further study showed that the transport ability of GmHKT1;1 regulated by GmHKT1;4 was related to the structural differences in the first intracellular domain and the fourth repeat domain. Overall, we have identified one unique GmHKT member, GmHKT1;4, which modulates the Na+ and K+ transport ability of GmHKT1;1 via direct interaction. Thus, we have revealed a new type of HKT interaction model for altering their ion transport properties.

Genome-wide identification and expressional analysis of carotenoid cleavage oxygenase (CCO) gene family in Betula platyphylla under abiotic stress

BACKGROUND

Carotenoid cleavage oxygenases (CCOs) are a group of enzymes that catalyze the oxidative cleavage of carotenoid molecules. These enzymes widely exist in plants, fungi, and certain bacteria, and are involved in various biological processes. It would be of great importance and necessity to identify CCO members in birch and characterize their responses upon abiotic stresses.

RESULTS

A total of 16 BpCCOs, including 8 BpCCDs and 8 BpNCEDs were identified in birch, and phylogenetic tree analysis showed that they could be classified into six subgroups. Collinearity analysis revealed that BpCCOs have the largest number of homologous genes in Gossypium hirsutum and also have more homologous genes in other dicotyledons. In addition, promoter analysis revealed that the promoter regions of BpCCOs contained many abiotic stress-related and hormone-responsive elements. The results of qRT-PCR showed that most of the BpCCOs were able to respond significantly to ABA, PEG, salt and cold stresses. Finally, the prediction of the interacting proteins of BpCCOs by STRING revealed several proteins that may interact with BpCCOs and be involved in plant growth and development/abiotic stress processes, such as HEC1 (bHLH), ATABA1, ATVAMP714, etc. CONCLUSION: In this study, the CCO members were identified in birch in a genome-wide scale. These results indicate that BpCCO genes may play important roles in the abiotic stress responses of birch plants.

Genome-Wide Identification and Expression Analyses of the Thaumatin-Like Protein Gene Family in Tetragonia tetragonoides (Pall.) Kuntze Reveal Their Functions in Abiotic Stress Responses

Thaumatin-like proteins (TLPs), including osmotins, are multifunctional proteins related to plant biotic and abiotic stress responses. TLPs are often present as large multigene families. Tetragonia tetragonoides (Pall.) Kuntze (Aizoaceae, 2n = 2x = 32), a vegetable used in both food and medicine, is a halophyte that is widely distributed in the coastal areas of the tropics and subtropics. Saline-alkaline soils and drought are two major abiotic stress factors significantly affecting the distribution of tropical coastal plants. The expression of stress resistance genes would help to alleviate the cellular damage caused by abiotic stress factors such as high temperature, salinity-alkalinity, and drought. This study aimed to better understand the functions of TLPs in the natural ecological adaptability of T. tetragonoides to harsh habitats. In the present study, we used bioinformatics approaches to identify 37 TtTLP genes as gene family members in the T. tetragonoides genome, with the purpose of understanding their roles in different developmental processes and the adaptation to harsh growth conditions in tropical coral regions. All of the TtTLPs were irregularly distributed across 32 chromosomes, and these gene family members were examined for conserved motifs of their coding proteins and gene structure. Expression analysis based on RNA sequencing and subsequent qRT-PCR showed that the transcripts of some TtTLPs were decreased or accumulated with tissue specificity, and under environmental stress challenges, multiple TtTLPs exhibited changeable expression patterns at short (2 h), long (48 h), or both stages. The expression pattern changes in TtTLPs provided a more comprehensive overview of this gene family being involved in multiple abiotic stress responses. Furthermore, several TtTLP genes were cloned and functionally identified using the yeast expression system. These findings not only increase our understanding of the role that TLPs play in mediating halophyte adaptation to extreme environments but also improve our knowledge of plant TLP evolution. This study also provides a basis and reference for future research on the roles of plant TLPs in stress tolerance and ecological environment suitability.

Iron transporter1 OsIRT1 positively regulates saline-alkaline stress tolerance in Oryza sativa

Soil salinization-alkalization severely affects plant growth and crop yield worldwide, especially in the Songnen Plain of Northeast China. Saline-alkaline stress increases the pH around the plant roots, thereby limiting the absorption and transportation of nutrients and ions, such as iron (Fe). Fe is an essential micronutrient that plays important roles in many metabolic processes during plant growth and development, and it is acquired by the root cells via iron-regulated transporter1 (IRT1). However, the function of Oryza sativa IRT1 (OsIRT1) under soda saline-alkaline stress remains unknown. Therefore, in this study, we generated OsIRT1 mutant lines and OsIRT1-overexpressing lines in the background of the O. sativa Songjing2 cultivar to investigate the roles of OsIRT1 under soda saline-alkaline stress. The OsIRT1-overexpressing lines exhibited higher tolerance to saline-alkaline stress compared to the mutant lines during germination and seedling stages. Moreover, the expression of some saline-alkaline stress-related genes and Fe uptake and transport-related genes were altered. Furthermore, Fe and Zn contents were upregulated in the OsIRT1-overexpressing lines under saline-alkaline stress. Further analysis revealed that Fe and Zn supplementation increased the tolerance of O. sativa seedlings to saline-alkaline stress. Altogether, our results indicate that OsIRT1 plays a significant role in O. sativa by repairing the saline-alkaline stress-induced damage. Our findings provide novel insights into the role of OsIRT1 in O. sativa under soda saline-alkaline stress and suggest that OsIRT1 can serve as a potential target gene for the development of saline-alkaline stress-tolerant O. sativa plants.

Biological Nano-Agrochemicals for Crop Production as an Emerging Way to Address Heat and Associated Stresses

Climate change is a global problem facing all aspects of the agricultural sector. Heat stress due to increasing atmospheric temperature is one of the most common climate change impacts on agriculture. Heat stress has direct effects on crop production, along with indirect effects through associated problems such as drought, salinity, and pathogenic stresses. Approaches reported to be effective to mitigate heat stress include nano-management. Nano-agrochemicals such as nanofertilizers and nanopesticides are emerging approaches that have shown promise against heat stress, particularly biogenic nano-sources. Nanomaterials are favorable for crop production due to their low toxicity and eco-friendly action. This review focuses on the different stresses associated with heat stress and their impacts on crop production. Nano-management of crops under heat stress, including the application of biogenic nanofertilizers and nanopesticides, are discussed. The potential and limitations of these biogenic nano-agrochemicals are reviewed. Potential nanotoxicity problems need more investigation at the local, national, and global levels, as well as additional studies into biogenic nano-agrochemicals and their effects on soil, plant, and microbial properties and processes.

Genome-wide identification and expression analysis of TPP gene family under salt stress in peanut (Arachis hypogaea L.)

Trehalose-6-phosphate phosphatase (TPP), a key enzyme for trehalose biosynthesis in plants, plays a pivotal role in the growth and development of higher plants, as well as their adaptations to various abiotic stresses. Employing bioinformatics techniques, 45 TPP genes distributed across 17 chromosomes were identified with conserved Trehalose-PPase domains in the peanut genome, aiming to screen those involved in salt tolerance. Collinearity analysis showed that 22 TPP genes from peanut formed homologous gene pairs with 9 TPP genes from Arabidopsis and 31 TPP genes from soybean, respectively. Analysis of cis-acting elements in the promoters revealed the presence of multiple hormone- and abiotic stress-responsive elements in the promoter regions of AhTPPs. Expression pattern analysis showed that members of the TPP gene family in peanut responded significantly to various abiotic stresses, including low temperature, drought, and nitrogen deficiency, and exhibited certain tissue specificity. Salt stress significantly upregulated AhTPPs, with a higher number of responsive genes observed at the seedling stage compared to the podding stage. The intuitive physiological effect was reflected in the significantly higher accumulation of trehalose content in the leaves of plants under salt stress compared to the control. These findings indicate that the TPP gene family plays a crucial role in peanut's response to abiotic stresses, laying the foundation for further functional studies and utilization of these genes.

Salinity-induced desertification in oasis ecosystems: challenges and future directions

Salinity-induced desertification is a pressing environmental issue that poses a significant threat to the sustainability of oasis ecosystems worldwide. These ecosystems are vital to the livelihoods of millions of people living in hyper-arid, arid and semi-arid regions, providing essential resources such as food, water and other necessities. However, overexploitation of natural resources, changes in land use and climate change have led to the degradation of these ecosystems, resulting in soil salinisation, waterlogging and other adverse effects. Combating salinity-induced desertification requires a comprehensive approach that addresses both the underlying causes of ecosystem degradation and the direct consequences for local communities. The strategy may include measures for sustainable land use, reforestation and water conservation. It is also essential to involve local communities in these activities and to ensure that their perspectives are heard. The aim of this article is to examine the causes and processes of salinity-induced desertification in oasis ecosystems and the implications for their sustainability. It also examines strategies that are being used to prevent desertification and promote sustainable oasis management. This article aims to raise awareness of this critical issue and to promote action towards a more sustainable future.

PagbHLH35 Enhances Salt Tolerance through Improving ROS Scavenging in Transgenic Poplar

The bHLH transcription factor family plays crucial roles in plant growth and development and their responses to adversity. In this study, a highly salt-induced bHLH gene, PagbHLH35 (Potri.018G141600), was identified from Populus alba × P. glandullosa (84K poplar). PagbHLH35 contains a highly conserved bHLH domain within the region of 52-114 amino acids. A subcellular localization result confirmed its nuclear localization. A yeast two-hybrid assay indicated PagbHLH35 lacks transcriptional activation activity, while a yeast one-hybrid assay indicated it could specifically bind to G-box and E-box elements. The expression of PagbHLH35 reached its peak at 12 h and 36 h time points under salt stress in the leaves and roots, respectively. A total of three positive transgenic poplar lines overexpressing PagbHLH35 were generated via Agrobacterium-mediated leaf disk transformation. Under NaCl stress, the transgenic poplars exhibited significantly enhanced morphological and physiological advantages such as higher POD activity, SOD activity, chlorophyll content, and proline content, and lower dehydration rate, MDA content and hydrogen peroxide (H2O2) content, compared to wild-type (WT) plants. In addition, histological staining showed that there was lower ROS accumulation in the transgenic poplars under salt stress. Moreover, the relative expression levels of several antioxidant genes in the transgenic poplars were significantly higher than those in the WT. All the results indicate that PagbHLH35 can improve salt tolerance by enhancing ROS scavenging in transgenic poplars.

Overexpression of Abscisic Acid Biosynthesis Gene OsNCED3 Enhances Survival Rate and Tolerance to Alkaline Stress in Rice Seedlings

Alkaline stress with high pH levels could significantly influence plant growth and survival. The enzyme 9-cis-epoxycarotenoid dioxygenase (NCED) serves as a critical bottleneck in the biosynthesis of abscisic acid (ABA), making it essential for regulating stress tolerance. Here, we show that OsNCED3-overexpressing rice lines have increased ABA content by up to 50.90% and improved transcription levels of numerous genes involved in stress responses that significantly enhance seedling survival rates. Overexpression of OsNCED3 increased the dry weight contents of the total chlorophyll, proline, soluble sugar, starch, and the activities of antioxidant enzymes of rice seedlings, while reducing the contents of O2·-, H2O2, and malondialdehyde under hydroponic alkaline stress conditions simulated by 10, 15, and 20 mmol L-1 of Na2CO3. Additionally, the OsNCED3-overexpressing rice lines exhibited a notable increase in the expression of OsNCED3; ABA response-related genes OsSalT and OsWsi18; ion homeostasis-related genes OsAKT1, OsHKT1;5, OsSOS1, and OsNHX5; and ROS scavenging-related genes OsCu/Zn-SOD, OsFe-SOD, OsPOX1, OsCATA, OsCATB, and OsAPX1 in rice seedling leaves. The results of these findings suggest that overexpression of OsNCED3 upregulates endogenous ABA levels and the expression of stress response genes, which represents an innovative molecular approach for enhancing the alkaline tolerance of rice seedlings.

Potassium transporter OsHAK17 may contribute to saline-alkaline tolerant mechanisms in rice (Oryza sativa)

Rice production is seriously affected by saline-alkaline stress worldwide. To elucidate the saline-alkaline tolerance mechanisms in a novel tolerant rice variety, Shwe Nang Gyi (SNG), we investigated ion accumulation in SNG and Koshihikari (KSH), which is a saline-alkaline sensitive rice variety, and the candidates for saline-alkaline inducible genes in SNG using RNA-seq. SNG had superior ion accumulation capacity, such as K and Zn, compared to KSH. In contrast, SNG accumulated the same level of Na content in its leaf blades as KSH despite the higher dry weight of the SNG leaf blades. We further found that the expression of numerous genes, including several K+ transporter/high-affinity K+ transporter/K+ uptake protein/K+ transporter (HAK/KUP/KT) family members, were upregulated in SNG, and that OsHAK17 and OsHAK21 expression levels in the roots were significantly higher in SNG than in KSH. Moreover, yeast complementation analysis revealed that OsHAK17 was involved in K+ uptake under high-Na conditions. These results suggested that SNG has an effective K+ acquisition system supported by OsHAK17 functioning in saline-alkaline environments.

A B-box transcription factor OsBBX17 regulates saline-alkaline tolerance through the MAPK cascade pathway in rice

Rice OsBBX17 encodes a B-box zinc finger transcription factor in which the N-terminal B-box structural domain interacts with OsMPK1. In addition, it directly binds to the G-box of OsHAK2 and OsHAK7 promoters and represses their transcription. Under saline-alkaline conditions, the expression of OsBBX17 was inhibited. Meanwhile, activation of the OsMPK1-mediated mitogen-activated protein kinase cascade pathway caused OsMPK1 to interact with OsBBX17 and phosphorylate OsBBX17 at the Thr-95 site. It reduced OsBBX17 DNA-binding activity and enhanced saline-alkaline tolerance by deregulating transcriptional repression of OsHAK2 and OsHAK7. Genetic assays showed that the osbbx17-KO had an excellent saline-alkaline tolerance, whereas the opposite was in OsBBX17-OE. In addition, overexpression of OsMPK1 significantly improved saline-alkaline tolerance, but knockout of OsMPK1 caused an increased sensitivity. Further overexpression of OsBBX17 in the osmpk1-KO caused extreme saline-alkaline sensitivity, even a quick death. OsBBX17 was validated in saline-alkaline tolerance from two independent aspects, transcriptional level and post-translational protein modification, unveiling a mechanistic framework by which OsMPK1-mediated phosphorylation of OsBBX17 regulates the transcription of OsHAK2 and OsHAK7 to enhance the Na+ /K+ homeostasis, which partially explains light on the molecular mechanisms of rice responds to saline-alkaline stress via B-box transcription factors for the genetic engineering of saline-alkaline tolerant crops.

Plasma membrane-localized H+-ATPase OsAHA3 functions in saline-alkaline stress tolerance in rice

KEY MESSAGE

A novel function of plasma membrane-localized H+-ATPase, OsAHA3, was identified in rice, which is involved in saline-alkaline tolerance and specifically responds to high pH during saline-alkaline stress. Saline-alkaline stress causes serious damage to crop production on irrigated land. Plants suffer more severe damage under saline-alkaline stress than under salinity stress alone. Plasma membrane-localized proton (H+) pump (H+-ATPase) is an important enzyme that controls plant growth and development by catalyzing H+ efflux and enabling effective charge balance. Many studies about the role of plasma membrane H+-ATPases in saline-alkaline stress tolerance have been reported in Arabidopsis, especially on the AtAHA2 (Arabidopsis thaliana H+-ATPase 2) gene; however, whether and how plasma membrane H+-ATPases play a role in saline-alkaline stress tolerance in rice remain unknown. Here, using the activation-tagged rice mutant pool, we found that the plasma membrane-localized H+-ATPase OsAHA3 (Oryza sativa autoinhibited H+-ATPase 3) is involved in saline-alkaline stress tolerance. Activation-tagged line 29 (AC29) was identified as a loss-of-function mutant of OsAHA3 and showed more severe growth retardation under saline-alkaline stress with high pH than under salinity stress. Moreover, osaha3 loss-of-function mutants generated by CRISPR/Cas9 system exhibited saline-alkaline stress sensitive phenotypes; staining of leaves with nitrotetrazolium blue chloride (NBT) and diaminobenzidine (DAB) revealed more reactive oxygen species (ROS) accumulation in osaha3 mutants. OsAHA3-overexpressing plants showed increased saline-alkaline stress tolerance than wild-type plants. Tissue-specific expression analysis revealed high expression level of OsAHA3 in leaf, sheath, glume, and panicle. Overall, our results revealed a novel function of plasma membrane-localized H+-ATPase, OsAHA3, which is involved in saline-alkaline stress tolerance and specifically responds to high pH.

Effects of NaHCO3 Stress on Black Locust (Robinia pseudoacacia L.) Physiology, Biochemistry, and Rhizosphere Bacterial Communities

Soil salinization has become an ecological and environmental problem that cannot be ignored. Tetraploid black locust (Robinia pseudoacacia L.) is a leguminous tree with characteristics of drought and saline-alkali tolerance. Rhizosphere bacteria are the primary functional microorganisms within the plant root system, and they play a crucial role in regulating plant growth and enhancing stress tolerance. However, there is still a lack of research on the effect of saline-alkali stress on the bacterial community structure in the rhizosphere of black locusts. In this study, we applied 0, 50, 100, and 150 mM NaHCO3 stress to diploid (2×) and tetraploid (4×) black locusts for 16 days. We used 16S rDNA sequencing to investigate the changes in the rhizosphere bacterial communities. Furthermore, we evaluated soil enzyme activity and plant physiological characteristics to explore the response of rhizosphere bacteria to NaHCO3 stress. The results demonstrated that the 4× plant exhibited superior alkali resistance compared to its 2× plant counterpart under NaHCO3 stress. Simultaneously, it was observed that low concentrations of NaHCO3 stress notably increased the abundance of rhizosphere bacteria in both plant types, while reducing their diversity. The impact of stress on the rhizosphere bacterial community weakened as the stress concentration increased. The application of NaHCO3 stress caused a significant change in the composition of the bacterial community in the rhizosphere. Additionally, alkaline salt stress influences the diversity of rhizosphere bacterial communities, which are linked to soil enzyme activities. These data will help us better understand the relationship between the dominant rhizosphere bacterial community and black locust. They will also provide a reference for further improving the alkali resistance of black locust by enhancing the soil bacterial community.

The Potential of Endophytes in Improving Salt-Alkali Tolerance and Salinity Resistance in Plants

Ensuring food security for the global population is a ceaseless and critical issue. However, high-salinity and high-alkalinity levels can harm agricultural yields throughout large areas, even in largely agricultural countries, such as China. Various physical and chemical treatments have been employed in different locations to mitigate high salinity and alkalinity but their effects have been minimal. Numerous researchers have recently focused on developing effective and environmentally friendly biological treatments. Endophytes, which are naturally occurring and abundant in plants, retain many of the same characteristics of plants owing to their simultaneous evolution. Therefore, extraction of endophytes from salt-tolerant plants for managing plant growth in saline-alkali soils has become an important research topic. This extraction indicates that the soil environment can be fundamentally improved, and the signaling pathways of plants can be altered to increase their defense capacity, and can even be inherited to ensure lasting efficacy. This study discusses the direct and indirect means by which plant endophytes mitigate the effects of plant salinity stress that have been observed in recent years.

A novel ABA-induced transcript factor from Millettia pinnata, MpAITR1, enhances salt and drought tolerance through ABA signaling in transgenic Arabidopsis

Abiotic stress, such as salt and drought stress, seriously limits plant growth and crop yield. Abscisic acid (ABA) is essential in regulating plant responses to abiotic stress via signal perception, transduction, and transcriptional regulation. Pongamia (Millettia pinnata) is a kind of semi-mangrove plant with strong stress tolerance and can grow in fresh and sea water. However, the molecular mechanism of the ABA signaling pathway mediating the environmental tolerance of Pongamia is still scarce so far. AITR (ABA-Induced Transcription Repressor) was a recently identified small conserved family of transcription factor in angiosperms, which played controversial roles in response to abiotic stresses in different species. Here, we identified an ABA-induced gene, MpAITR1, which encoded a nucleus localization transcriptional factor in Pongamia. MpAITR1 was highly induced by ABA and salt treatments in roots and leaves. Heterologous expression of MpAITR1 in Arabidopsis increased sensitivity to ABA, moreover, enhanced tolerance to salt and drought stress. The expression levels of some ABA-responsive and stress-responsive genes were altered in transgenic plants compared to wild-type plants under the ABA, salt, and drought stress, which was consistent with the stress-tolerant phenotype of transgenic plants. These results reveal that MpAITR1 positively modulates ABA signaling pathways and enhances the tolerance to salt and drought stress by regulating downstream target genes. Taken together, MpAITR1 from the semi-mangrove plant Pongamia serves as a potential candidate for stress-tolerant crop breeding.

Multi-Omics Revealed Peanut Root Metabolism Regulated by Exogenous Calcium under Salt Stress

High salinity severely inhibits plant seedling root development and metabolism. Although plant salt tolerance can be improved by exogenous calcium supplementation, the metabolism molecular mechanisms involved remain unclear. In this study, we integrated three types of omics data (transcriptome, metabolome, and phytohormone absolute quantification) to analyze the metabolic profiles of peanut seedling roots as regulated by exogenous calcium under salt stress. (1) exogenous calcium supplementation enhanced the allocation of carbohydrates to the TCA cycle and plant cell wall biosynthesis rather than the shikimate pathway influenced by up-regulating the gene expression of antioxidant enzymes under salt stress; (2) exogenous calcium induced further ABA accumulation under salt stress by up-regulating the gene expression of ABA biosynthesis key enzymes AAO2 and AAO3 while down-regulating ABA glycosylation enzyme UGT71C5 expression; (3) exogenous calcium supplementation under salt stress restored the trans-zeatin absolute content to unstressed levels while inhibiting the root cis-zeatin biosynthesis.

GsPKS24, a calcineurin B-like protein-interacting protein kinase gene from Glycine soja, positively regulates tolerance to pH stress and ABA signal transduction

SOS2-like protein kinases (PKS/CIPK) family genes are known to be involved in various abiotic stresses in plants. Even though, its functions have been well characterized under salt and drought stresses. The roles of PKS genes associated with alkaline stress response are not fully established yet. In this study, we identified 56 PKS family genes which could be mainly classified into three groups in wild soybean (Glycine soja). PKS family genes transcript profiles revealed different expression patterns under alkali stress. Furthermore, we confirmed the regulatory roles of GsPKS24 in response to NaHCO3, pH and ABA treatments. Overexpression of GsPKS24 enhanced plant tolerance to pH stress in Arabidopsis and soybean hairy roots but conferred suppressed pH tolerance in Arabidopsis atpks mutant. Additionally, Overexpression of GsPKS24 decreased the ABA sensitivity compared to Arabidopsis atpks mutant which displayed more sensitivity towards ABA. Moreover, upregulated expression of stress responsive and ABA signal-related genes were detected in GsPKS24 overexpression lines. In conclusion, we identified the wild soybean PKS family genes, and explored the roles of GsPKS24 in positive response to pH stress tolerance, and in alleviation of ABA sensitivity.

Integrated Transcriptomic and Metabolomic Analyses Uncover the Differential Mechanism in Saline-Alkaline Tolerance between Indica and Japonica Rice at the Seedling Stage

Saline-alkaline stress is one of the major damages that severely affects rice (Oryza sativa L.) growth and grain yield; however, the mechanism of the tolerance remains largely unknown in rice. Herein, we comparatively investigated the transcriptome and metabolome of two contrasting rice subspecies genotypes, Luohui 9 (abbreviation for Chao2R under study, O. sativa ssp. indica, saline-alkaline-sensitive) and RPY geng (O. sativa ssp. japonica, saline-alkaline-tolerant), to identify the main pathways and important factors related to saline-alkaline tolerance. Transcriptome analysis showed that 68 genes involved in fatty acid, amino acid (such as phenylalanine and tryptophan), phenylpropanoid biosynthesis, energy metabolism (such as Glycolysis and TCA cycle), as well as signal transduction (such as hormone and MAPK signaling) were identified to be specifically upregulated in RPY geng under saline-alkaline conditions, implying that a series of cascade changes from these genes promotes saline-alkaline stress tolerance. The transcriptome changes observed in RPY geng were in high accordance with the specifically accumulation of metabolites, consisting mainly of 14 phenolic acids, 8 alkaloids, and 19 lipids based on the combination analysis of transcriptome and metabolome. Moreover, some genes involved in signal transduction as hub genes, such as PR5, FLS2, BRI1, and NAC, may participate in the saline-alkaline stress response of RPY geng by modulating key genes involved in fatty acid, phenylpropanoid biosynthesis, amino acid metabolism, and glycolysis metabolic pathways based on the gene co-expression network analysis. The present research results not only provide important insights for understanding the mechanism underlying of rice saline-alkaline tolerance at the transcriptome and metabolome levels but also provide key candidate target genes for further enhancing rice saline-alkaline stress tolerance.

Exploration of the Regulatory Pathways and Key Genes Involved in the Response to Saline-Alkali Stress in Betula platyphylla via RNA-Seq Analysis

The pH of saline-alkali soil is high because of carbonate salts, and the deleterious effects of saline-alkali soil on the growth of plants are greater than those of saline soil. Few studies have examined the saline-alkali tolerance of Betula platyphylla at the molecular level. To clarify the regulatory mechanism underlying saline-alkali tolerance in B. platyphylla, RNA sequencing analysis of B. platyphylla seedlings treated with NaHCO₃ was conducted. Differences in gene expression in the roots of B. platyphylla seedlings under saline-alkali stress (induced via NaHCO₃) for 3 h and 6 h were characterized, and a total of 595 and 607 alkali stress-responsive genes were identified, respectively. Most differentially expressed genes were involved in stress, signal transduction, secondary metabolic process, regulation of jasmonic acid, and the abiotic stimulus signaling pathway. The single nucleotide polymorphism loci in the differentially expressed genes were associated with the alkaline-salt tolerance in birch germplasm. In addition, birch plants overexpressing WRKY70 and NAC9 were obtained using the A. tumefaciens-mediated transient transformation method, and these two genes were found to play key roles in saline-alkali tolerance. Additional study revealed that WRKY70 and NAC9 can increase resistance to saline-alkali stress by enhancing reactive oxygen species scavenging and inhibiting cell death in birch plants. The results of this study enhance our understanding of the saline-alkali stress tolerance of B. platyphylla at the molecular level, and provide several key genes that could be used in the breeding of birch plants in the future.

Transmembrane potential, an indicator in situ reporting cellular senescence and stress response in plant tissues

BACKGROUND

Plant cells usually sustain a stable membrane potential due to influx and/or efflux of charged ions across plasma membrane. With the growth and development of plants, different tissues and cells undergo systemic or local programmed decline. Whether the membrane potential of plasma membrane could report senescence signal of plant tissues and cells is unclear.

RESULTS

We applied a maneuverable transmembrane potential (TMP) detection method with patch-clamp setup to examine the senescence signal of leaf tissue cells in situ over the whole life cycle in Arabidopsis thaliana. The data showed that the TMPs of plant tissues and cells were varied at different growth stages, and the change of TMP was higher at the vegetative growth stage than at the reproductive stage of plant growth. The distinct change of TMP was detectable between the normal and the senescent tissues and cells in several plant species. Moreover, diverse abiotic stimuli, such as heat stress, hyperpolarized the TMP in a short time, followed by depolarized membrane potential with the senescence occurring. We further examined the TMP of plant chloroplasts, which also indicates the senescence signal in organelles.

CONCLUSIONS

This convenient TMP detection method can report the senescence signal of plant tissues and cells, and can also indicate the potential of plant tolerance to environmental stress.

Tissue Culture—A Sustainable Approach to Explore Plant Stresses

Plants are constantly faced with biotic or abiotic stress, which affects their growth and development. Yield reduction due to biotic and abiotic stresses on economically important crop species causes substantial economic loss at a global level. Breeding for stress tolerance to create elite and superior genotypes has been a common practice for many decades, and plant tissue culture can be an efficient and cost-effective method. Tissue culture is a valuable tool to develop stress tolerance, screen stress tolerance, and elucidate physiological and biochemical changes during stress. In vitro selection carried out under controlled environment conditions in confined spaces is highly effective and cheaper to maintain. This review emphasizes the relevance of plant tissue culture for screening major abiotic stresses, drought, and salinity, and the development of disease resistance. Further emphasis is given to screening metal hyperaccumulators and transgenic technological applications for stress tolerance.