PAMP-INDUCED SECRETED PEPTIDE 3 modulates salt tolerance through RECEPTOR-LIKE KINASE 7 in plants

MdMAPK3-driven phosphorylation enhances MdWRKY17-mediated regulation of high-affinity K+ transporter 1 MdHAK1 for salt tolerance in apple

Salt stress is a major environmental factor that limits the growth and yield of apple (Malus domestica), but the underlying mechanism of apple salt tolerance remains unclear. In this study, we uncovered a critical pathway involving the transcription factor MdWRKY17, which positively regulates salt tolerance in apple. MdWRKY17 directly binds to the promoter of MdHAK1 (High-affinity K+ transporter 1) and activates its expression. MdHAK1 encodes a plasma membrane-localized transporter that regulates Na+ and K+ homeostasis under salt stress, playing an essential role in maintaining ionic balance. Additionally, we demonstrated that the salt-inducible kinase MdMAPK3 phosphorylates MdWRKY17, enhancing its transcriptional activation of MdHAK1 under salt stress conditions. Collectively, the identification of the MdMAPK3-MdWRKY17-MdHAK1 pathway represents a coordinated mechanism integrating transcriptional regulation, ion transport, and post-translational modifications, offering valuable insights for breeding salt-tolerant apple varieties.

VvprePIP, the Precursor of a PAMP-Induced Secreted Peptide, Stimulates Defence Responses and Improves Resistance to Plasmopora viticola in Grapevine

PRRs (Pattern-Recognition Receptors) distributed on plant cell membranes recognize not only PAMPs (Pathogen-Associated Molecular Patterns) released from the pathogens but also ligand peptides secreted from the plants, followed by eliciting defence responses. Here, we demonstrate that transcription of VvprePIP from grape (Vitis vinifera) encoding the precursor of a PIP (PAMP-Induced secreted Peptide) peptide is activated by Plasmopara viticola infection. Overexpression of VvprePIP increases the expression of defence-related genes and ROS (Reactive Oxygen Species) production, enhancing resistance to P. viticola in V. vinifera. A WRKY transcription factor VvWRKY8 interacts with VvprePIP promoter, upregulating its transcription directly. The immune reactions resulting from ectopic expression of VvprePIP are impaired in NbBAK1-silencing tobacco, implying BAK1 is necessary for the recognition between mature peptide VvPIP and its receptor. The conserved region at the C terminus of VvprePIP carries three typical SGPS-GH motifs, all of which contribute to provoke immune responses in plant. As synthetic VvPIP with a hydroxylated modification at the forth proline can mimic the functions of overexpression of the precursor, while synthetic unmodified VvPIP cannot, we reported that hydroxyproline is required for VvPIPs to serve as an active signal molecular. In conclusion, our studies reveal that VvprePIP plays a role in enhancing plant resistance to pathogens.

Research progress of peptides discovery and function in resistance to abiotic stress in plant

Plant peptides play crucial roles in various biological processes, including stress responses. This study investigates the functions of plant peptides in response to different adversity stresses, focusing on drought, salt, high temperature, and other environmental challenges. In drought conditions, specific peptides such as CLE25 and CLE9 were found to regulate stomatal closure and root architecture to enhance the efficiency of water utilization. Salt stress induces the expression of CAPE1 and CEP3, which are involved in ion homeostasis and osmoregulation, thereby contributing to salt tolerance in plants. Heat stress triggers the expression of peptides such as CEL45, which contributes to the heat tolerance of cells. Besides, we have also verified a new class of non-conventional peptides, and a large number of non-conventional peptides have been identified in rice seedlings. Understanding the origin and functions of these peptides presents both challenges and opportunities for developing stress-resistant crops. Future research should focus on elucidating the precise molecular mechanisms of peptide-mediated stress responses and exploring their potential applications in agriculture and biotechnology.

Response of different cotton genotypes to salt stress and re-watering

BACKGROUND

Cotton is a vital economic crop and reserve material and a pioneer crop planted on saline-alkaline soil. Improving the tolerance of cotton to saline alkaline environments is particularly important.

RESULTS

Salt-tolerant and salt-sensitive cotton plants at the three-leaf stage were subjected to 200 mM NaCl stress treatment, thereafter, microstructural observations beside physiological and biochemical analyses were performed on cotton leaves at 0 h (CK), 48 h (NaCl) and re-watering (RW) for 48 h. Salt stress altered microstructural observations and physiological and biochemical in ST and SS (p < 0.05). After re-watering, ST recovered fully, while SS sustained permanent oxidative and structural damage, indicating distinct salt tolerance. Transcriptome analysis was performed on cotton leaves under salt stress and re-watering conditions. KEGG analysis revealed that the response of cotton to salt stress and its adaptation to re-watering may be related to major protein families such as photosynthesis (ko 00195), photosynthesis-antenna protein (ko 00196), plant hormone signal transduction (ko 04075), starch and sucrose metabolism (ko 00500), and porphyrin and chlorophyll metabolism (ko 00860). A gray coexpression module associated with cotton restoration under salt stress was enriched according to WGCNA.

CONCLUSIONS

Salt stress did not only affect the physiological and biochemical levels of cotton but also induced structural changes in cells and tissues. Re-watering was relatively effective in stabilizing the physiological and biochemical parameters, as well as the leaf microstructure, of cotton plants under salt stress. WGCNA revealed enriched gray coexpression modules related to the recovery of cotton plants under salt stress, and screening of the pivotal genes in the gray module revealed five critical hubs, namely, GH_A01G1528, GH_A08G2688, GH_D08G2683, GH_D01G1620 and GH_A10G0617. Overall, our findings can provide new insights into enhancing cotton salt tolerance and exploring salt tolerance genes in cotton,including screening cotton genetic resources using those potential responsive genes. This study provides a theoretical basis for further exploration of the molecular mechanism of cotton salt tolerance and genetic resources for breeding salt-tolerant cotton.

Multiple layers of regulators emerge in the network controlling lateral root organogenesis

Lateral root (LR) formation is a postembryonic organogenesis process that is crucial for plant root system development and adaptation to heterogenous soil environments. Since the early 1990s, a wealth of experimental data on arabidopsis (Arabidopsis thaliana) has helped reveal the LR formation regulatory network, in which dynamic auxin distribution and transcriptional cascades direct root cells through their organogenesis pathway. Some parts of this network appear conserved across diverse plant species or distinct developmental contexts. Recently, our knowledge of this process dramatically expanded thanks to technical advances, from single cell profiling to whole-root system phenotyping. Interestingly, new players are now emerging in this network, such as fatty acids and reactive oxygen species (ROS), transforming our knowledge of this hidden half of plant biology.

Comprehensive review of plant small signaling peptides: From stress adaptation mechanisms to practical solutions for crop resilience

Small signaling peptides (SSPs), short proteins of fewer than 100 amino acids, serve as pivotal signaling molecules with diverse structural features, post-translational modifications, and functional roles. They regulate various aspects of plant growth and development by modulating specific cellular signaling pathways. Research has shown that many SSPs are essential for mediating responses to environmental stresses. This review presents the structure, characteristics, and classification of plant SSPs and elucidates their roles in resistance signaling pathways through interactions with their specific receptors. We then summarize recent findings on the biological functions and regulatory mechanisms of SSPs in response to both biotic and abiotic stresses. Finally, we discuss the potential applications and future prospects of these peptides in plant protection. This review offers valuable insights for enhancing plant resilience to environmental stress and advancing sustainable agricultural practices, while also providing key references and perspectives to accelerate research on SSPs in plants.

Decoding small peptides: Regulators of plant growth and stress resilience

Small peptides (SPs) are pivotal signaling molecules that play essential roles in the precise regulation of plant growth, development, and stress responses. Recent advancements in sequencing technologies, bioinformatics approaches, and biochemical and molecular techniques have significantly enhanced the accuracy of SP identification, unveiling their diverse biological functions in plants. This review provides a comprehensive overview of the characteristics and methodologies for identifying SPs in plants. It highlights recent discoveries regarding the biological roles and signaling pathways of SPs in regulating plant growth, development, and plant-microbial interactions, as well as their contributions to plant resilience under various environmental stresses, including abiotic stress, nutrient deficiencies, and biotic challenges. Additionally, we discuss current insights into the potential applications of SPs and outline future research directions aimed at leveraging these molecules to enhance plant adaptation to environmental challenges. By integrating recent findings, this review lays a foundation for advancing the understanding and utilization of SPs to improve plant resilience and productivity.

The interaction of nutrient uptake with biotic and abiotic stresses in plants

Plants depend heavily on efficient nutrient uptake and utilization for optimal growth and development. However, plants are constantly subjected to a diverse array of biotic stresses, such as pathogen infections, insect pests, and herbivory, as well as abiotic stress like drought, salinity, extreme temperatures, and nutrient imbalances. These stresses significantly impact the plant's ability to take up nutrient and use it efficiency. Understanding how plants maintain nutrient uptake and use efficiency under biotic and abiotic stress conditions is crucial for improving crop resilience and sustainability. This review explores the recent advancements in elucidating the mechanisms underlying nutrient uptake and utilization efficiency in plants under such stress conditions. Our aim is to offer a comprehensive perspective that can guide the breeding of stress-tolerant and nutrition-efficient crop varieties, ultimately contributing to the advancement of sustainable agriculture.

ZmSIDP1, a DUF1644 gene from the halophyte Zoysia matrella, positively regulates salt tolerance in rice

As a detrimental abiotic stressor, salinity affects plant growth and yield. Domain of unknown function 1644 (DUF1644) is a large plant-specific DUF protein family that is predicted to be involved in abiotic stress responses in plants. However, the biological functions of DUF1644 genes in plants remain largely unexplored, especially in halophytes. Here, we investigated the function of the DUF1644 gene, ZmSIDP1, from the halophyte Zoysia matrella. ZmSIDP1 could enhance the salt tolerance of yeast. Furthermore, the heterologous transformation of the ZmSIDP1 gene in rice demonstrated that transgenic rice plants exhibited better growth under NaCl treatment. The Na + content was lower in ZmSIDP1 transgenic rice than in wild-type rice under salt stress. ZmSIDP1 transgenic rice showed stronger resistance to oxidative stress induced by salt stress. Further investigation indicated that ZmSIDP1 could interact with an HD-Zip transcription factor, ZmROC1. These results suggest that the ZmSIDP1 gene from the halophyte Z. matrella can positively regulate salt resistance in rice, laying a foundation for the application of salt tolerance genes from halophytes to enhance salt tolerance in rice.

Functional and transcriptomic characterization of the receptor-like protein kinase gene GmHSL1b involved in salt stress tolerance in soybean roots

The survival and adaptation of plants to adverse environmental conditions is crucial and is facilitated by receptor-like kinases, which act as cell surface receptors for a variety of signals. In this study, we identified a gene, GmHSL1b, encoding a receptor-like protein kinase that is responsive to abscisic acid (ABA) hormonal signals and is involved in the plant's response to drought and salt stresses. Subcellular localization assays have demonstrated that the GmHSL1b protein is located in the plasma membrane. Overexpression of the GmHSL1b gene in soybean enhanced root growth and development, as well as the plant's tolerance to salt stress, while the gmhsl1b mutant revealed increased sensitivity to salt stress. Comparative transcriptome analysis showed that some genes associated with various biological processes, such as mitogen-activated protein kinase (MAPK) cascade signaling, plant hormone signaling, cell wall remodeling, calcium signaling, and defense response mechanisms are differentially expressed in GmHSL1b overexpressing roots. Our research indicated that GmHSL1b can regulate the expression level of the candidate aquaporin GmPIP2-1, thereby affecting cell water content and the accumulation of reactive oxygen species (ROS) under salt stress. These findings indicate that the GmHSL1b participates in regulating root development and enhancing the tolerance to salt stress, thus offering insights for boosting crop adaptability to environmental stresses.

Salinity survival: molecular mechanisms and adaptive strategies in plants

Soil salinity is a significant environmental challenge that threatens plant growth and development, adversely affecting global food crop production. This underscores the critical need to elucidate the molecular mechanisms underlying plant salt tolerance, which has profound implications for agricultural advancement. Recent progress in plant salt tolerance has greatly improved our understanding of the molecular mechanisms of plant responses to salt stress and precision design breeding as an effective strategy for developing new salt-tolerant crop varieties. This review focuses on the model plant species Arabidopsis thaliana and important crops, namely, wheat (Triticum aestivum), maize (Zea mays), and rice (Oryza sativa). It summarizes current knowledge on plant salt tolerance, emphasizing key aspects such as the perception and response to salt stress, Na+ transport, Na+ compartmentalization and clearance, changes in reactive oxygen species induced by salt stress, and regulation of plant stem cell development under salt stress conditions. The review might provide new and valuable information for understanding the molecular mechanisms of plant response and adaptation to salt stress.

Genome-Wide Identification and Functional Analysis of CLAVATA3/EMBRYO SURROUNDING REGION-RELATED (CLE) in Three Populus Species

Intercellular communication mediated by CLAVATA3/EMBRYO SURROUNDING REGION-RELATED (CLE) peptides and their receptors is crucial for plant development and environmental adaptation. In this study, 45 and 89 CLEs were identified in Populus tomentosa and Populus alba × Populus glandulosa, respectively, and, together with the 52 CLEs in Populus trichocarpa, the chromosome localization, gene and protein characteristics, collinearity and gene duplication events, cis-acting regulatory elements in promoters and evolutionary relationships of CLEs in these three poplar species were analyzed. The CLEs of three poplar species were divided into four subfamilies. Among them, the CLEs in subfamilies I, II and IV were A-type CLEs, while those in subfamily III were B-type CLEs. During the evolutionary process of poplar, the selection pressure faced by whole-genome duplication or segmental duplication was purifying selection, and the duplication events led to the expansion of the CLE family in poplar. The exogenous addition of a certain concentration of poplar CLE13 peptides inhibits the root growth of Arabidopsis thaliana and poplar and simultaneously reduces the expression levels of ARFs and LBDs in the roots. In addition, drought stress induces the expression of PtrCLE13A. The overexpression of preCLE13A significantly enhances the osmotic and drought tolerance in Populus tomentosa. These results have provided valuable information for further research on the molecular mechanisms of CLE peptide signaling pathways in the woody model plant poplar regarding plant growth and stress resistance.

Current progress in deciphering the molecular mechanisms underlying plant salt tolerance

Enhancing crop salt tolerance through genetics and genomics is important for food security. It is environmentally friendly and cost-effective in maintaining crop production in farmlands affected by soil salinization and can also facilitate the utilization of marginal saline land. Despite the limited success achieved so far, it is becoming possible to bridge the gap between fundamental research and crop breeding owing to a deeper understanding of plant salt tolerance at both physiological and molecular levels. Therefore, we review the recent key progress in identifying the molecular mechanisms contributing to plant salt tolerance with a focus on balancing growth and salt resilience. With the accruing knowledge and the rapidly evolving tools (e.g. genome editing and artificial intelligence), it is reasonable to expect the future salt-tolerant crops in a few decades.

Genome-wide identification, characterization, and functional analysis of the CHX, SOS, and RLK genes in Solanum lycopersicum under salt stress

The cation/proton exchanger (CHX), salt overly sensitive (SOS), and receptor-like kinase (RLK) genes play significant roles in the response to salt stress in plants. This study is the first to identify the SOS gene in Solanum lycopersicum (tomato) through genome-wide analysis under salt stress conditions. Quantitative reverse transcription PCR (qRT-PCR) results indicated that the expression levels of CHX, SOS, and RLK genes were upregulated, with fold changes of 1.83, 1.49, and 1.55, respectively, after 12 h of exposure to salt stress. Genome-wide analysis revealed 21 CHX, 5 SOS, and 86 RLK genes in S. lycopersicum. CHX genes were found on chromosomes 2, 3, 4, 5, 6, 7, 8, 9, 11, and 12 of S. lycopersicum. SOS genes were found on chromosomes 1, 4, 6, and 10. RLK genes were found on all chromosomes of S. lycopersicum. The Ka/Ks ratios indicate that the CHX, SOS, and RLK genes have been primarily influenced by purifying selection. This suggests that these genes have faced strong environmental pressures throughout their evolution. Purifying selection typically results in a decrease in genetic diversity. The estimated duplication time for CHX paralogous gene pairs ranged from approximately 26.965 to 245.413 million years ago (Mya), while the duplication time for SOS paralogous gene pairs ranged from around 116.682 to 275.631 Mya. For RLK paralogous gene pairs, the duplication time varied from approximately 27.689 to 239.376 Mya. Synteny analysis of the CHX, SOS, and RLK genes demonstrated collinear relationships with orthologous genes in Arabidopsis thaliana, but no collinearity orthologous relationships in Oryza sativa (rice). Furthermore, the analysis revealed that there were 6 orthologous SlCHX genes, 2 orthologous SlSOS genes, and 44 orthologous SlRLK genes paired with those in A. thaliana. The results of the present study may help to elucidate the role of the CHX, SOS, and RLK genes in salt stress in S. lycopersicum.

Two leucine-rich repeat receptor-like kinases initiate herbivory defense responses in tea plants

Leucine-rich repeat receptor-like kinases (LRR-RLKs) have emerged as key regulators of herbivory perception and subsequent defense initiation. While their functions in grass plants have been gradually elucidated, the roles of herbivory-related LRR-RLKs in woody plants remain largely unknown. In this study, we mined the genomic and transcriptomic data of tea plants (Camellia sinensis) and identified a total of 307 CsLRR-RLK members. Phylogenetic analysis grouped these CsLRR-RLKs into 14 subgroups along with their Arabidopsis homologs. Gene structure and conserved domain analyses revealed notable similarities among subgroup members. Among the identified CsLRR-RLKs, we focused on two plasma membrane-localized LRR-RLKs, CsLRR-RLK44, and CsLRR-RLK239, which do not form homodimers or heterodimers with each other. Both respond strongly to herbivory, and their expression patterns significantly correlate with herbivore resistance phenotypes across different tea accessions. CsLRR-RLK44 and CsLRR-RLK239 act upstream of mitogen-activated protein kinase (MPK) cascades and modulate the expression of defense-related MPKs and WRKY transcription factors. Additionally, silencing CsLRR-RLK44 or CsLRR-RLK239 reduced the levels of herbivory-induced jasmonates, thereby weakening the plant resistance to tea geometrid larvae (Ectropis obliqua). Our work is the first to demonstrate that in woody plants, LRR-RLKs are essential for enhancing herbivore resistance through the activation of the canonical signaling, including MPKs, WRKYs, and jasmonates. Furthermore, our study extends mechanistic insights into how LRR-RLKs initiate plant defenses from grasses to economically important tree species.

CALMODULIN-BINDING RECEPTOR-LIKE CYTOPLASMIC KINASE 3 regulates salt tolerance through CATALASE 2 in Arabidopsis

Soil salinization threatens global crop production. Here, we report that a receptor-like cytoplasmic kinase, CALMODULIN-BINDING RECEPTOR-LIKE CYTOPLASMIC KINASE 3 (CRCK3), plays an essential role in plant salt tolerance via CATALASE 2 (CAT2), a hydrogen peroxide (H2O2)-scavenging enzyme in Arabidopsis (Arabidopsis thaliana). CRCK3 was induced by salt stress, and its knockout mutant displayed a salt-sensitive phenotype compared with wild-type plants. CRCK3 was activated by salt stress in a calcium-dependent manner, and its kinase activity was required for plant salt tolerance. CRCK3 physically interacted with CAT2, and CRCK3-mediated salt tolerance depended on CAT2. Salt treatment significantly induced CAT2 phosphorylation via the action of CRCK3, and this phosphorylation was required for CAT2-mediated H2O2 scavenging to reduce reactive oxygen species (ROS) content and oxidative damage in plants under saline conditions. CRCK3 phosphorylated CAT2 at the Thr209 residue, resulting in elevated catalase activity to reduce ROS accumulation under saline conditions. Therefore, the CRCK3-CAT2 module mediates plant salt tolerance by maintaining redox homeostasis. This study expands our knowledge of how plants respond to salt stress.

SORTING NEXIN1 facilitates SALT OVERLY SENSITIVE1 protein accumulation to enhance salt tolerance in Arabidopsis

The plasma membrane (PM)-localized Na+/H+ antiporter Salt Overly Sensitive1 (SOS1) is essential for plant salt tolerance through facilitating Na+ efflux; however, how SOS1 localization and protein accumulation is regulated in plants remains elusive. Here, we report that Sorting Nexin 1 (SNX1) is required for plant salt-stress tolerance through affecting endosomal trafficking of SOS1 in Arabidopsis (Arabidopsis thaliana). Disruption of SNX1 caused salt hypersensitivity with increased Na+ accumulation and decreased Na+ efflux in Arabidopsis when challenged with high salinity stress. SNX1 co-localized and interacted with SOS1 in endosomes, promoting its PM localization and protein stability in plants under saline conditions. SOS1 overexpression promoted salt tolerance in the wild-type, whereas such effect was greatly compromised in the snx1-2 mutant. Pharmaceutical results showed that SOS1 recycling from the cytosol to the PM was largely blocked while its vacuolar degradation was accelerated in the snx1-2 mutant. Furthermore, salt-induced SOS1 phosphorylation enhanced its interaction and co-localization with SNX1, which is required for SOS1 PM localization in plants. Our study elucidates that SNX1 facilitates SOS1 PM localization and protein accumulation through endosomal trafficking, thereby enhancing salt tolerance in plants.

CEP signaling coordinates plant immunity with nitrogen status

Plant endogenous signaling peptides shape growth, development and adaptations to biotic and abiotic stress. Here, we identify C-TERMINALLY ENCODED PEPTIDEs (CEPs) as immune-modulatory phytocytokines in Arabidopsis thaliana. Our data reveals that CEPs induce immune outputs and are required to mount resistance against the leaf-infecting bacterial pathogen Pseudomonas syringae pv. tomato. We show that effective immunity requires CEP perception by tissue-specific CEP RECEPTOR 1 (CEPR1) and CEPR2. Moreover, we identify the related RECEPTOR-LIKE KINASE 7 (RLK7) as a CEP4-specific CEP receptor contributing to CEP-mediated immunity, suggesting a complex interplay of multiple CEP ligands and receptors in different tissues during biotic stress. CEPs have a known role in the regulation of root growth and systemic nitrogen (N)-demand signaling. We provide evidence that CEPs and their receptors promote immunity in an N status-dependent manner, suggesting a previously unknown molecular crosstalk between plant nutrition and cell surface immunity. We propose that CEPs and their receptors are central regulators for the adaptation of biotic stress responses to plant-available resources.

Imaging the spatial distribution of structurally diverse plant hormones

Plant hormones are essential and structurally diverse molecules that regulate various aspects of plant growth, development, and stress responses. However, the precise analysis of plant hormones in complex biological samples poses a challenge due to their low concentrations, dynamic levels, and intricate spatial distribution. Moreover, the complexity and interconnectedness of hormone signaling networks make it difficult to simultaneously trace multiple hormone spatial distributions. In this review, we provide an overview of currently recognized small-molecule plant hormones, signal peptide hormones, and plant growth regulators, along with the analytical methods employed for their analysis. We delve into the latest advancements in mass spectrometry imaging and in situ fluorescence techniques, which enable the examination of the spatial distribution of plant hormones. The advantages and disadvantages of these imaging techniques are further discussed. Finally, we propose potential avenues in imaging techniques to further enhance our understanding of plant hormone biology.

The MdHSC70-MdWRKY75 module mediates basal apple thermotolerance by regulating the expression of heat shock factor genes

Heat stress severely restricts the growth and fruit development of apple (Malus domestica). Little is known about the involvement of WRKY proteins in the heat tolerance mechanism in apple. In this study, we found that the apple transcription factor (TF) MdWRKY75 responds to heat and positively regulates basal thermotolerance. Apple plants that overexpressed MdWRKY75 were more tolerant to heat stress while silencing MdWRKY75 caused the opposite phenotype. RNA-seq and reverse transcription quantitative PCR showed that heat shock factor genes (MdHsfs) could be the potential targets of MdWRKY75. Electrophoretic mobility shift, yeast one-hybrid, β-glucuronidase, and dual-luciferase assays showed that MdWRKY75 can bind to the promoters of MdHsf4, MdHsfB2a, and MdHsfA1d and activate their expression. Apple plants that overexpressed MdHsf4, MdHsfB2a, and MdHsfA1d exhibited heat tolerance and rescued the heat-sensitive phenotype of MdWRKY75-Ri3. In addition, apple heat shock cognate 70 (MdHSC70) interacts with MdWRKY75, as shown by yeast two-hybrid, split luciferase, bimolecular fluorescence complementation, and pull-down assays. MdHSC70 acts as a negative regulator of the heat stress response. Apple plants that overexpressed MdHSC70 were sensitive to heat, while virus-induced gene silencing of MdHSC70 enhanced heat tolerance. Additional research showed that MdHSC70 exhibits heat sensitivity by interacting with MdWRKY75 and inhibiting MdHsfs expression. In summary, we proposed a mechanism for the response of apple to heat that is mediated by the "MdHSC70/MdWRKY75-MdHsfs" molecular module, which enhances our understanding of apple thermotolerance regulated by WRKY TFs.

Small Peptides: Orchestrators of Plant Growth and Developmental Processes

Small peptides (SPs), ranging from 5 to 100 amino acids, play integral roles in plants due to their diverse functions. Despite their low abundance and small molecular weight, SPs intricately regulate critical aspects of plant life, including cell division, growth, differentiation, flowering, fruiting, maturation, and stress responses. As vital mediators of intercellular signaling, SPs have garnered significant attention in plant biology research. This comprehensive review delves into SPs' structure, classification, and identification, providing a detailed understanding of their significance. Additionally, we summarize recent findings on the biological functions and signaling pathways of prominent SPs that regulate plant growth and development. This review also offers a perspective on future research directions in peptide signaling pathways.

Alternative Splicing Plays a Crucial Role in the Salt Tolerance of Foxtail Millet

Foxtail millet is an important cereal crop that is relatively sensitive to salt stress, with its yield significantly affected by such stress. Alternative splicing (AS) widely affects plant growth, development, and adaptability to stressful environments. Through RNA-seq analysis of foxtail millet under different salt treatment periods, 2078 AS events were identified, and analyses were conducted on differential gene (DEG), differential alternative splicing gene (DASG), and overlapping gene. To investigate the regulatory mechanism of AS in response to salt stress in foxtail millet, the foxtail millet AS genes SiCYP19, with two AS variants (SiCYP19-a and SiCYP19-b), were identified and cloned. Yeast overexpression experiments indicated that SiCYP19 may be linked to the response to salt stress. Subsequently, we conducted overexpression experiments of both alternative splicing variants in foxtail millet roots to validate them experimentally. The results showed that, under salt stress, both SiCYP19-a and SiCYP19-b jointly regulated the salt tolerance of foxtail millet. Specifically, overexpression of SiCYP19-b significantly increased the proline content and reduced the accumulation of reactive oxygen species (ROS) in foxtail millet, compared to that in SiCYP19-a. This shows that SiCYP19-b plays an important role in increasing the content of proline and promoting the clearance of ROS, thus improving the salt tolerance of foxtail millet.

Zinc Oxide Nanoparticles Alleviate Salt Stress in Cotton (Gossypium hirsutum L.) by Adjusting Na+/K+ Ratio and Antioxidative Ability

Soil salinization poses a threat to the sustainability of agricultural production and has become a global issue. Cotton is an important cash crop and plays an important role in economic development. Salt stress has been harming the yield and quality of many crops, including cotton, for many years. In recent years, soil salinization has been increasing. It is crucial to study the mechanism of cotton salt tolerance and explore diversified materials and methods to alleviate the salt stress of cotton for the development of the cotton industry. Nanoparticles (NPs) are an effective means to alleviate salt stress. In this study, zinc oxide NPs (ZnO NPs) were sprayed on cotton leaves with the aim of investigating the intrinsic mechanism of NPs to alleviate salt stress in cotton. The results show that the foliar spraying of ZnO NPs significantly alleviated the negative effects of salt stress on hydroponic cotton seedlings, including the improvement of above-ground and root dry and fresh weight, leaf area, seedling height, and stem diameter. In addition, ZnO NPs can significantly improve the salt-induced oxidative stress by reducing the levels of MDA, H2O2, and O2- and increasing the activities of major antioxidant enzymes, such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). Furthermore, RNA-seq showed that the foliar spraying of ZnO NPs could induce the expressions of CNGC, NHX2, AHA3, HAK17, and other genes, and reduce the expression of SKOR, combined with the CBL-CIPK pathway, which alleviated the toxic effect of excessive Na+ and reduced the loss of excessive K+ so that the Na+/K+ ratio was stabilized. In summary, our results indicate that the foliar application of ZnO NPs can alleviate high salt stress in cotton by adjusting the Na+/K+ ratio and regulating antioxidative ability. This provides a new strategy for alleviating the salt stress of cotton and other crops, which is conducive to the development of agriculture.

Research Progress of Small Plant Peptides on the Regulation of Plant Growth, Development, and Abiotic Stress

Small peptides in plants are typically characterized as being shorter than 120 amino acids, with their biologically active variants comprising fewer than 20 amino acids. These peptides are instrumental in regulating plant growth, development, and physiological processes, even at minimal concentrations. They play a critical role in long-distance signal transduction within plants and act as primary responders to a range of stress conditions, including salinity, alkalinity, drought, high temperatures, and cold. This review highlights the crucial roles of various small peptides in plant growth and development, plant resistance to abiotic stress, and their involvement in long-distance transport. Furthermore, it elaborates their roles in the regulation of plant hormone biosynthesis. Special emphasis is given to the functions and mechanisms of small peptides in plants responding to abiotic stress conditions, aiming to provide valuable insights for researchers working on the comprehensive study and practical application of small peptides.

Designing salt stress-resilient crops: Current progress and future challenges

Excess soil salinity affects large regions of land and is a major hindrance to crop production worldwide. Therefore, understanding the molecular mechanisms of plant salt tolerance has scientific importance and practical significance. In recent decades, studies have characterized hundreds of genes associated with plant responses to salt stress in different plant species. These studies have substantially advanced our molecular and genetic understanding of salt tolerance in plants and have introduced an era of molecular design breeding of salt-tolerant crops. This review summarizes our current knowledge of plant salt tolerance, emphasizing advances in elucidating the molecular mechanisms of osmotic stress tolerance, salt-ion transport and compartmentalization, oxidative stress tolerance, alkaline stress tolerance, and the trade-off between growth and salt tolerance. We also examine recent advances in understanding natural variation in the salt tolerance of crops and discuss possible strategies and challenges for designing salt stress-resilient crops. We focus on the model plant Arabidopsis (Arabidopsis thaliana) and the four most-studied crops: rice (Oryza sativa), wheat (Triticum aestivum), maize (Zea mays), and soybean (Glycine max).

Translatome and Transcriptome Analyses Reveal the Mechanism that Underlies the Enhancement of Salt Stress by the Small Peptide Ospep5 in Plants

Salt stress significantly impedes plant growth and the crop yield. This study utilized de novo transcriptome assembly and ribosome profiling to explore mRNA translation's role in rice salt tolerance. We identified unrecognized translated open reading frames (ORFs), including 42 upstream transcripts and 86 unannotated transcripts. A noteworthy discovery was the role of a small ORF, Ospep5, in conferring salt tolerance. Overexpression of Ospep5 in plants increased salt tolerance, while its absence led to heightened sensitivity. This hypothesis was corroborated by the findings that exogenous application of the synthetic small peptide Ospep5 bolstered salt tolerance in both rice and Arabidopsis. We found that the mechanism underpinning the Ospep5-mediated salt tolerance involves the maintenance of intracellular Na+/K+ homeostasis, facilitated by upregulation of high-affinity potassium transporters (HKT) and Na+/H+ exchangers (SOS1). Furthermore, a comprehensive multiomics approach, particularly ribosome profiling, is instrumental in uncovering unannotated ORFs and elucidating their functions in plant stress responses.

Genome-wide identification of the LRR-RLK gene family in peanut and functional characterization of AhLRR-RLK265 in salt and drought stresses

Leucine-rich repeat receptor-like kinases (LRR-RLKs) play important roles in plant developmental regulations and various stress responses. Peanut (Arachis hypogaea L.) is a worldwide important oil crop; however, no systematic identification or analysis of the peanut LRR-RLK gene family has been reported. In present study, 495 LRR-RLK genes in peanut were identified and analyzed. The 495 AhLRR-RLK genes were classed into 14 groups and 10 subgroups together with their Arabidopsis homologs according to phylogenetic analyses, and 491 of 495 AhLRR-RLK genes unequally located on 20 chromosomes. Analyses of gene structure and protein motif organization revealed similarity in exon/intron and motif organization among members of the same subgroup, further supporting the phylogenetic results. Gene duplication events were found in peanut LRR-RLK gene family via syntenic analysis, which were important in LRR-RLK gene family expansion in peanut. We found that the expression of AhLRR-RLK genes was detected in different tissues using RNA-seq data, implying that AhLRR-RLK genes may differ in function. In addition, Arabidopsis plants overexpressing stress-induced AhLRR-RLK265 displayed lower seed germination rates and root lengths compared to wild-type under exogenous ABA treatment. Notably, overexpression of AhLRR-RLK265 enhanced tolerance to salt and drought stresses in transgenic Arabidopsis. Moreover, the AhLRR-RLK265-OE lines were found to have higher activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) under salt and drought stress treatments. We believe these results may provide valuable information about the function of peanut LRR-RLK genes for further analysis.

Insights into plant salt stress signaling and tolerance

Soil salinization is an essential environmental stressor, threatening agricultural yield and ecological security worldwide. Saline soils accumulate excessive soluble salts which are detrimental to most plants by limiting plant growth and productivity. It is of great necessity for plants to efficiently deal with the adverse effects caused by salt stress for survival and successful reproduction. Multiple determinants of salt tolerance have been identified in plants, and the cellular and physiological mechanisms of plant salt response and adaption have been intensely characterized. Plants respond to salt stress signals and rapidly initiate signaling pathways to re-establish cellular homeostasis with adjusted growth and cellular metabolism. This review summarizes the advances in salt stress perception, signaling, and response in plants. A better understanding of plant salt resistance will contribute to improving crop performance under saline conditions using multiple engineering approaches. The rhizosphere microbiome-mediated plant salt tolerance as well as chemical priming for enhanced plant salt resistance are also discussed in this review.

Emerging Roles of Receptor-like Protein Kinases in Plant Response to Abiotic Stresses

The productivity of plants is hindered by unfavorable conditions. To perceive stress signals and to transduce these signals to intracellular responses, plants rely on membrane-bound receptor-like kinases (RLKs). These play a pivotal role in signaling events governing growth, reproduction, hormone perception, and defense responses against biotic stresses; however, their involvement in abiotic stress responses is poorly documented. Plant RLKs harbor an N-terminal extracellular domain, a transmembrane domain, and a C-terminal intracellular kinase domain. The ectodomains of these RLKs are quite diverse, aiding their responses to various stimuli. We summarize here the sub-classes of RLKs based on their domain structure and discuss the available information on their specific role in abiotic stress adaptation. Furthermore, the current state of knowledge on RLKs and their significance in abiotic stress responses is highlighted in this review, shedding light on their role in influencing plant-environment interactions and opening up possibilities for novel approaches to engineer stress-tolerant crop varieties.

Small secreted peptides (SSPs) in tomato and their potential roles in drought stress response

Tomato (Solanum lycopersicum) is one of the most important vegetable crops in the world and abiotic stresses often cause serious problems in tomato production. It is thus important to identify new regulators in stress response and to devise new approaches to promote stress tolerance in tomato. Previous studies have shown that small secreted peptides (SSPs) are important signal molecules regulating plant growth and stress response by mediating intercellular communication. However, little is known about tomato SSPs, especially their roles in responding to abiotic stresses. Here we report the identification of 1,050 putative SSPs in the tomato genome, 557 of which were classified into 38 known SSP families based on their conserved domains. GO and transcriptome analyses revealed that a large proportion of SlSSPs might be involved in abiotic stress response. Further analysis indicated that stress response related cis-elements were present on the SlCEP promotors and a number of SlCEPs were significantly upregulated by drought treatments. Among the drought-inducible SlCEPs, SlCEP10 and SlCEP11b were selected for further analysis via exogenous application of synthetic peptides. The results showed that treatments with both SlCEP10 and SlCEP11b peptides enhanced tomato drought stress tolerance, indicating the potential roles of SlSSPs in abiotic stress response.

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.

CycC1;1-WRKY75 complex-mediated transcriptional regulation of SOS1 controls salt stress tolerance in Arabidopsis

SALT OVERLY SENSITIVE1 (SOS1) is a key component of plant salt tolerance. However, how SOS1 transcription is dynamically regulated in plant response to different salinity conditions remains elusive. Here, we report that C-type Cyclin1;1 (CycC1;1) negatively regulates salt tolerance by interfering with WRKY75-mediated transcriptional activation of SOS1 in Arabidopsis (Arabidopsis thaliana). Disruption of CycC1;1 promotes SOS1 expression and salt tolerance in Arabidopsis because CycC1;1 interferes with RNA polymerase II recruitment by occupying the SOS1 promoter. Enhanced salt tolerance of the cycc1;1 mutant was completely compromised by an SOS1 mutation. Moreover, CycC1;1 physically interacts with the transcription factor WRKY75, which can bind to the SOS1 promoter and activate SOS1 expression. In contrast to the cycc1;1 mutant, the wrky75 mutant has attenuated SOS1 expression and salt tolerance, whereas overexpression of SOS1 rescues the salt sensitivity of wrky75. Intriguingly, CycC1;1 inhibits WRKY75-mediated transcriptional activation of SOS1 via their interaction. Thus, increased SOS1 expression and salt tolerance in cycc1;1 were abolished by WRKY75 mutation. Our findings demonstrate that CycC1;1 forms a complex with WRKY75 to inactivate SOS1 transcription under low salinity conditions. By contrast, under high salinity conditions, SOS1 transcription and plant salt tolerance are activated at least partially by increased WRKY75 expression but decreased CycC1;1 expression.

Drought stress tolerance mechanisms and their potential common indicators to salinity, insights from the wild watermelon (Citrullus lanatus): A review

Climate change has escalated the effect of drought on crop production as it has negatively altered the environmental condition. Wild watermelon grows abundantly in the Kgalagadi desert even though the environment is characterized by minimal rainfall, high temperatures and intense sunshine during growing season. This area is also characterized by sandy soils with low water holding capacity, thus bringing about drought stress. Drought stress affects crop productivity through its effects on development and physiological functions as dictated by molecular responses. Not only one or two physiological process or genes are responsible for drought tolerance, but a combination of various factors do work together to aid crop tolerance mechanism. Various studies have shown that wild watermelon possess superior qualities that aid its survival in unfavorable conditions. These mechanisms include resilient root growth, timely stomatal closure, chlorophyll fluorescence quenching under water deficit as key physiological responses. At biochemical and molecular level, the crop responds through citrulline accumulation and expression of genes associated with drought tolerance in this species and other plants. Previous salinity stress studies involving other plants have identified citrulline accumulation and expression of some of these genes (chloroplast APX, Type-2 metallothionein), to be associated with tolerance. Emerging evidence indicates that the upstream of functional genes are the transcription factor that regulates drought and salinity stress responses as well as adaptation. In this review we discuss the drought tolerance mechanisms in watermelons and some of its common indicators to salinity at physiological, biochemical and molecular level.

Plant salt response: Perception, signaling, and tolerance

Salt stress is one of the significant environmental stressors that severely affects plant growth and development. Plant responses to salt stress involve a series of biological mechanisms, including osmoregulation, redox and ionic homeostasis regulation, as well as hormone or light signaling-mediated growth adjustment, which are regulated by different functional components. Unraveling these adaptive mechanisms and identifying the critical genes involved in salt response and adaption are crucial for developing salt-tolerant cultivars. This review summarizes the current research progress in the regulatory networks for plant salt tolerance, highlighting the mechanisms of salt stress perception, signaling, and tolerance response. Finally, we also discuss the possible contribution of microbiota and nanobiotechnology to plant salt tolerance.

Silveira S, Brommonschenkel SH, Fontes EPB. RLPredictiOme, a Machine Learning-Derived Method for High-Throughput Prediction of Plant Receptor-like Proteins, Reveals Novel Classes of Transmembrane Receptors

Cell surface receptors play essential roles in perceiving and processing external and internal signals at the cell surface of plants and animals. The receptor-like protein kinases (RLK) and receptor-like proteins (RLPs), two major classes of proteins with membrane receptor configuration, play a crucial role in plant development and disease defense. Although RLPs and RLKs share a similar single-pass transmembrane configuration, RLPs harbor short divergent C-terminal regions instead of the conserved kinase domain of RLKs. This RLP receptor structural design precludes sequence comparison algorithms from being used for high-throughput predictions of the RLP family in plant genomes, as has been extensively performed for RLK superfamily predictions. Here, we developed the RLPredictiOme, implemented with machine learning models in combination with Bayesian inference, capable of predicting RLP subfamilies in plant genomes. The ML models were simultaneously trained using six types of features, along with three stages to distinguish RLPs from non-RLPs (NRLPs), RLPs from RLKs, and classify new subfamilies of RLPs in plants. The ML models achieved high accuracy, precision, sensitivity, and specificity for predicting RLPs with relatively high probability ranging from 0.79 to 0.99. The prediction of the method was assessed with three datasets, two of which contained leucine-rich repeats (LRR)-RLPs from Arabidopsis and rice, and the last one consisted of the complete set of previously described Arabidopsis RLPs. In these validation tests, more than 90% of known RLPs were correctly predicted via RLPredictiOme. In addition to predicting previously characterized RLPs, RLPredictiOme uncovered new RLP subfamilies in the Arabidopsis genome. These include probable lipid transfer (PLT)-RLP, plastocyanin-like-RLP, ring finger-RLP, glycosyl-hydrolase-RLP, and glycerophosphoryldiester phosphodiesterase (GDPD, GDPDL)-RLP subfamilies, yet to be characterized. Compared to the only Arabidopsis GDPDL-RLK, molecular evolution studies confirmed that the ectodomain of GDPDL-RLPs might have undergone a purifying selection with a predominance of synonymous substitutions. Expression analyses revealed that predicted GDPGL-RLPs display a basal expression level and respond to developmental and biotic signals. The results of these biological assays indicate that these subfamily members have maintained functional domains during evolution and may play relevant roles in development and plant defense. Therefore, RLPredictiOme provides a framework for genome-wide surveys of the RLP superfamily as a foundation to rationalize functional studies of surface receptors and their relationships with different biological processes.

Small secreted peptides encoded on the wheat (triticum aestivum L.) genome and their potential roles in stress responses

Small secreted peptides (SSPs) are important signals for cell-to-cell communication in plant, involved in a variety of growth and developmental processes, as well as responses to stresses. While a large number of SSPs have been identified and characterized in various plant species, little is known about SSPs in wheat, one of the most important cereal crops. In this study, 4,981 putative SSPs were identified on the wheat genome, among which 1,790 TaSSPs were grouped into 38 known SSP families. The result also suggested that a large number of the putaitive wheat SSPs, Cys-rich peptides in particular, remained to be characterized. Several TaSSP genes were found to encode multiple SSP domains, including CLE, HEVEIN and HAIRPININ domains, and two potentially novel TaSSP family DYY and CRP8CI were identified manually among unpredicted TaSSPs. Analysis on the transcriptomic data showed that a great proportion of TaSSPs were expressed in response to abiotic stresses. Exogenous application of the TaCEPID peptide encoded by TraesCS1D02G130700 enhanced the tolerance of wheat plants to drought and salinity, suggesting porential roles of SSPs in regulating stress responses in wheat.

Regulation of pattern-triggered immunity and growth by phytocytokines

Endogenous signalling peptides play diverse roles during plant growth, development and stress responses. Research in recent years has unravelled peptides with previously known growth-regulatory function as immune-modulatory agents that fine-tune pattern-triggered immunity (PTI). Moreover, peptides that are long known as endogenous danger signals were recently implicated in growth and development. In analogy to metazoan systems these peptides are referred to as phytocytokines. In this review we will highlight recent progress made on our understanding of phytocytokines simultaneously regulating growth and PTI which shows the complex interplay of peptide signalling pathways regulating multiple aspects of a plant's life.

Genome-Wide Characterization of the Aquaporin Gene Family in Radish and Functional Analysis of RsPIP2-6 Involved in Salt Stress

Aquaporins (AQPs) constitute a highly diverse family of channel proteins that transport water and neutral solutes. AQPs play crucial roles in plant development and stress responses. However, the characterization and biological functions of RsAQPs in radish (Raphanus sativus L.) remain elusive. In this study, 61 non-redundant members of AQP-encoding genes were identified from the radish genome database and located on nine chromosomes. Radish AQPs (RsAQPs) were divided into four subfamilies, including 21 plasma membrane intrinsic proteins (PIPs), 19 tonoplast intrinsic proteins (TIPs), 16 NOD-like intrinsic proteins (NIPs), and 5 small basic intrinsic proteins (SIPs), through phylogenetic analysis. All RsAQPs contained highly conserved motifs (motifs 1 and 4) and transmembrane regions, indicating the potential transmembrane transport function of RsAQPs. Tissue- and stage-specific expression patterns of AQP gene analysis based on RNA-seq data revealed that the expression levels of PIPs were generally higher than TIPs, NIPs, and SIPs in radish. In addition, quantitative real-time polymerase chain reaction (qRT-PCR) revealed that seven selected RsPIPs, according to our previous transcriptome data (e.g., RsPIP1-3, 1-6, 2-1, 2-6, 2-10, 2-13, and 2-14), exhibited significant upregulation in roots of salt-tolerant radish genotype. In particular, the transcriptional levels of RsPIP2-6 dramatically increased after 6 h of 150 mM NaCl treatment during the taproot thickening stage. Additionally, overexpression of RsPIP2-6 could enhance salt tolerance by Agrobacterium rhizogenes-mediated transgenic radish hairy roots, which exhibited the mitigatory effects of plant growth reduction, leaf relative water content (RWC) reduction and alleviation of O2- in cells, as shown by nitro blue tetrazolium (NBT) staining, under salt stress. These findings are helpful for deeply dissecting the biological function of RsAQPs on the salt stress response, facilitating practical application and genetic improvement of abiotic stress resistance in radish.

The INFLORESCENCE DEFICIENT IN ABSCISSION-LIKE6 Peptide Functions as a Positive Modulator of Leaf Senescence in Arabidopsis thaliana

Leaf senescence is a highly coordinated process and has a significant impact on agriculture. Plant peptides are known to act as important cell-to-cell communication signals that are involved in multiple biological processes such as development and stress responses. However, very limited number of peptides has been reported to be associated with leaf senescence. Here, we report the characterization of the INFLORESCENCE DEFICIENT IN ABSCISSION-LIKE6 (IDL6) peptide as a regulator of leaf senescence. The expression of IDL6 was up-regulated in senescing leaves. Exogenous application of synthetic IDL6 peptides accelerated the process of leaf senescence. The idl6 mutant plants showed delayed natural leaf senescence as well as senescence included by darkness, indicating a regulatory role of IDL6 peptides in leaf senescence. The role of IDL6 as a positive regulator of leaf senescence was further supported by the results of overexpression analysis and complementation test. Transcriptome analysis revealed differential expression of phytohormone-responsive genes in idl6 mutant plants. Further analysis indicated that altered expression of IDL6 led to changes in leaf senescence phenotypes induced by ABA and ethylene treatments. The results from this study suggest that the IDL6 peptide positively regulates leaf senescence in Arabidopsis thaliana.

Mucilaginibacter sp. K Improves Growth and Induces Salt Tolerance in Nonhost Plants via Multilevel Mechanisms

Soil salinity negatively modulates plant growth and development, contributing to severe decreases in the growth and production of crops. Mucilaginibacter sp. K is a root endophytic bacterium that was previously reported by our laboratory to stimulate growth and confer salt tolerance in Arabidopsis (Arabidopsis thaliana). The main purpose of the present study is to elucidate the physiological and molecular machinery responsible for the prospective salt tolerance as imparted by Mucilaginibacter sp. K. We first report that auxin, gibberellin, and MPK6 signalings were required for strain K-induced growth promotion and salt tolerance in Arabidopsis. Then, this strain was assessed as a remediation strategy to improve maize performance under salinity stress. Under normal growth conditions, the seed vigor index, nitrogen content, and plant growth were significantly improved in maize. After NaCl exposure, strain K significantly promoted the growth of maize seedlings, ameliorated decline in chlorophyll content and reduced accretion of MDA and ROS compared with the control. The possible mechanisms involved in salt resistance in maize could be the improved activities of SOD and POD (antioxidative system) and SPS (sucrose biosynthesis), upregulated content of total soluble sugar and ABA, and reduced Na⁺ accumulation. These physiological changes were then confirmed by induced gene expression for ion transportation, photosynthesis, ABA biosynthesis, and carbon metabolism. In summary, these results suggest that strain K promotes plant growth through increases in photosynthesis and auxin- and MPK6-dependent pathways; it also bestows salt resistance on plants through protection against oxidative toxicity, Na⁺ imbalance, and osmotic stress, along with the activation of auxin-, gibberellin-, and MPK6-dependent signaling pathways. This is the first detailed report of maize growth promotion by a Mucilaginibacter sp. strain from wild plant. This strain could be used as a favorable biofertilizer and a salinity stress alleviator for maize, with further ascertainment as to its reliability of performance under field conditions and in the presence of salt stress.

Molecular Mechanisms of Plant Responses to Salt Stress

Saline-alkali soils pose an increasingly serious global threat to plant growth and productivity. Much progress has been made in elucidating how plants adapt to salt stress by modulating ion homeostasis. Understanding the molecular mechanisms that affect salt tolerance and devising strategies to develop/breed salt-resilient crops have been the primary goals of plant salt stress signaling research over the past few decades. In this review, we reflect on recent major advances in our understanding of the cellular and physiological mechanisms underlying plant responses to salt stress, especially those involving temporally and spatially defined changes in signal perception, decoding, and transduction in specific organelles or cells.