Interruption of Jasmonic Acid Biosynthesis Causes Differential Responses in the Roots and Shoots of Maize Seedlings against Salt Stress

Bioinformatics, expression analysis, and functional verification of allene oxide synthase gene HvnAOS1 and HvnAOS2 in qingke

Allene oxide synthase (AOS) is a key enzyme involved in the jasmonic acid (JA) synthesis pathway in plants. To explore its function on the regulatory mechanism of JA synthesis, we screened and identified two AOS genes HvnAOS1 and HvnAOS2 in qingke. Both HvnAOS1 and HvnAOS2 contained conserved heme-binding motif, which is most closely related to AtsAOS2, indicating controlled dehydration of fatty acid hydroperoxides to allene oxides. Molecular docking simulations identified the key amino acid sites that were important for heme binding and interaction with 13(S)-HPOT, respectively. The expression pattern also indicated that HvnAOS1 and HvnAOS2 were highly induced by JA, abscisic acid, and salicylic acid. Subcellular localization of HvnAOS1 and HvnAOS2 using transient expression of Agrobacterium tumefaciens showed the green fluorescent protein signal in the cell cytoplasm of the N. benthamiana leaves. Overexpression of HvnAOS1 and HvnAOS2 in Arabidopsis aos mutant restored male fertility and plant resistance to Botrytis cinerea, indicating that HvnAOS1 and HvnAOS2 can restore the functions of AOS in Arabidopsis aos mutant.

SlWRKY80-mediated jasmonic acid pathway positively regulates tomato resistance to saline-alkali stress by enhancing spermidine content and stabilizing Na+/K+ homeostasis

Saline-alkali is an important abiotic stressor influencing tomato production. Exogenous methyl jasmonate (MeJA) is well known to increase tomato resistance to a variety of stresses, although its exact mechanism is yet unknown. In this study we confirmed that 22.5 μmol/l MeJA could significantly improve the saline-alkali stress resistance of tomato. Saline-alkali (300 mM) stress increased the endogenous MeJA and jasmonic acid (JA) contents of tomato by 18.8 and 13.4%, respectively. Exogenous application of 22.5 μmol/l MeJA increased the endogenous MeJA and JA contents in tomato by 15.2 and 15.9%, respectively. Furthermore, we found an important transcription factor, SlWRKY80, which responded to MeJA, and constructed its overexpressing and knockout lines through genetic transformation. It was found that SlWRKY80 actively regulated tomato resistance to saline-alkali stress, and the spraying of exogenous MeJA (22.5 μmol/l) reduced the sensitivity of SlWRKY80 knockout lines to saline-alkali stress. The SlWRKY80 protein directly combines with the promoter of SlSPDS2 and SlNHX4 to positively regulate the transcription of SlSPDS2 and SlNHX4, thereby promoting the synthesis of spermidine and Na+/K+ homeostasis, actively regulating saline-alkali stress. The augmentation of JA content led to a notable reduction of 70.6% in the expression of SlJAZ1, and the release of the SlWRKY80 protein interacting with SlJAZ1. In conclusion, we revealed the mechanism of exogenous MeJA in tomato stress resistance through multiple metabolic pathways, elucidated that exogenous MeJA further promotes spermidine synthesis and Na+/K+ homeostasis by activating the expression of SlWRKY80, which provides a new theoretical basis for the study of the JA stress resistance mechanism and the production of tomato.

Halomonas ventosae JPT10 promotes salt tolerance in foxtail millet (Setaria italica) by affecting the levels of multiple antioxidants and phytohormones

Plant growth-promoting bacterias (PGPBs) can increase crop output under normal and abiotic conditions. However, the mechanisms underlying the plant salt tolerance-promoting role of PGPBs still remain largely unknown. In this study, we demonstrated that Halomonas ventosae JPT10 promoted the salt tolerance of both dicots and monocots. Physiological analysis revealed that JPT10 reduced reactive oxygen species accumulation by improving the antioxidant capability of foxtail millet seedlings. The metabolomic analysis of JPT10-inoculated foxtail millet seedlings led to the identification of 438 diversely accumulated metabolites, including flavonoids, phenolic acids, lignans, coumarins, sugar, alkaloids, organic acids, and lipids, under salt stress. Exogenous apigenin and chlorogenic acid increased the salt tolerance of foxtail millet seedlings. Simultaneously, JPT10 led to greater amounts of abscisic acid (ABA), indole-3-acetic acid (IAA), salicylic acid (SA), and their derivatives but lower levels of 12-oxo-phytodienoic acid (OPDA), jasmonate (JA), and JA-isoleucine (JA-Ile) under salt stress. Exogenous JA, methyl-JA, and OPDA intensified, whereas ibuprofen or phenitone, two inhibitors of JA and OPDA biosynthesis, partially reversed, the growth inhibition of foxtail millet seedlings caused by salt stress. Our results shed light on the response of foxtail millet seedlings to H. ventosae under salt stress and provide potential compounds to increase salt tolerance in foxtail millet and other crops.

Transcriptomic analysis reveals that methyl jasmonate confers salt tolerance in alfalfa by regulating antioxidant activity and ion homeostasis

Introduction

Alfalfa, a globally cultivated forage crop, faces significant challenges due to its vulnerability to salt stress. Jasmonates (JAs) play a pivotal role in modulating both plant growth and response to stressors.

Methods

In this study, alfalfa plants were subjected to 150 mM NaCl with or without methyl jasmonate (MeJA). The physiological parameters were detected and a transcriptomic analysis was performed to elucidate the mechanisms underlying MeJA-mediated salt tolerance in alfalfa.

Results

Results showed that exogenous MeJA regulated alfalfa seed germination and primary root growth in a dose-dependent manner, with 5µM MeJA exerting the most efficient in enhancing salt tolerance. MeJA at this concentration elavated the salt tolerance of young alfalfa seedlings by refining plant growth, enhancing antioxidant capacity and ameliorating Na+ overaccumulation. Subsequent transcriptomic analysis identified genes differentially regulated by MeJA+NaCl treatment and NaCl alone. PageMan analysis revealed several significantly enriched categories altered by MeJA+NaCl treatment, compared with NaCl treatment alone, including genes involved in secondary metabolism, glutathione-based redox regulation, cell cycle, transcription factors (TFs), and other signal transductions (such as calcium and ROS). Further weighted gene co-expression network analysis (WGCNA) uncovered that turquoise and yellow gene modules were tightly linked to antioxidant enzymes activity and ion content, respectively. Pyruvate decar-boxylase (PDC) and RNA demethylase (ALKBH10B) were identified as the most central hub genes in these two modules. Also, some TFs-hub genes were identified by WGCNA in these two modules highly positive-related to antioxidant enzymes activity and ion content.

Discussion

MeJA triggered a large-scale transcriptomic remodeling, which might be mediated by transcriptional regulation through TFs or post-transcriptional regulation through demethylation. Our findings contributed new perspectives for understanding the underneath mechanisms by which JA-mediated salt tolerance in alfalfa.

Signal Mediators in the Implementation of Jasmonic Acid's Protective Effect on Plants under Abiotic Stresses

Plant cells respond to stress by activating signaling and regulatory networks that include plant hormones and numerous mediators of non-hormonal nature. These include the universal intracellular messenger calcium, reactive oxygen species (ROS), gasotransmitters, small gaseous molecules synthesized by living organisms, and signal functions such as nitrogen monoxide (NO), hydrogen sulfide (H₂S), carbon monoxide (CO), and others. This review focuses on the role of functional linkages of jasmonic acid and jasmonate signaling components with gasotransmitters and other signaling mediators, as well as some stress metabolites, in the regulation of plant adaptive responses to abiotic stressors. Data on the involvement of NO, H₂S, and CO in the regulation of jasmonic acid formation in plant cells and its signal transduction were analyzed. The possible involvement of the protein components of jasmonate signaling in stress-protective gasotransmitter effects is discussed. Emphasis is placed on the significance of the functional interaction between jasmonic acid and signaling mediators in the regulation of the antioxidant system, stomatal apparatus, and other processes important for plant adaptation to abiotic stresses.

Research Progress on the Mechanism of Salt Tolerance in Maize: A Classic Field That Needs New Efforts

Maize is the most important cereal crop globally. However, in recent years, maize production faced numerous challenges from environmental factors due to the changing climate. Salt stress is among the major environmental factors that negatively impact crop productivity worldwide. To cope with salt stress, plants developed various strategies, such as producing osmolytes, increasing antioxidant enzyme activity, maintaining reactive oxygen species homeostasis, and regulating ion transport. This review provides an overview of the intricate relationships between salt stress and several plant defense mechanisms, including osmolytes, antioxidant enzymes, reactive oxygen species, plant hormones, and ions (Na⁺, K⁺, Cl^-), which are critical for salt tolerance in maize. It addresses the regulatory strategies and key factors involved in salt tolerance, aiming to foster a comprehensive understanding of the salt tolerance regulatory networks in maize. These new insights will also pave the way for further investigations into the significance of these regulations in elucidating how maize coordinates its defense system to resist salt stress.

Ketols Emerge as Potent Oxylipin Signals Regulating Diverse Physiological Processes in Plants

Plants produce an array of oxylipins implicated in defense responses against various stresses, with about 600 oxylipins identified in plants to date. Most known oxylipins are the products of lipoxygenase (LOX)-mediated oxygenation of polyunsaturated fatty acids. One of the most well-characterized oxylipins produced by plants is the hormone jasmonic acid (JA); however, the function of the vast majority of oxylipins remains a mystery. One of the lesser-studied groups of oxylipins is comprised of ketols produced by the sequential action of LOX, allene oxide synthase (AOS), followed by non-enzymatic hydrolysis. For decades, ketols were mostly considered mere by-products of JA biosynthesis. Recent accumulating evidence suggests that ketols exhibit hormone-like signaling activities in the regulation of diverse physiological processes, including flowering, germination, plant-symbiont interactions, and defense against biotic and abiotic stresses. To complement multiple reviews on jasmonate and overall oxylipin biology, this review focuses specifically on advancing our understanding of ketol biosynthesis, occurrence, and proposed functions in diverse physiological processes.

Jasmonate signaling controls negative and positive effectors of salt stress tolerance in rice

Plant responses to salt exposure involve large reconfigurations of hormonal pathways that orchestrate physiological changes towards tolerance. Jasmonate (JA) hormones are essential to withstand biotic and abiotic assaults, but their roles in salt tolerance remain unclear. Here we describe the dynamics of JA metabolism and signaling in root and leaf tissue of rice, a plant species that is highly exposed and sensitive to salt. Roots activate the JA pathway in an early pulse, while the second leaf displays a biphasic JA response with peaks at 1 h and 3 d post-exposure. Based on higher salt tolerance of a rice JA-deficient mutant (aoc), we examined, through kinetic transcriptome and physiological analysis, the salt-triggered processes that are under JA control. Profound genotype-differential features emerged that could underlie the observed phenotypes. Abscisic acid (ABA) content and ABA-dependent water deprivation responses were impaired in aoc shoots. Moreover, aoc accumulated more Na+ in roots, and less in leaves, with reduced ion translocation correlating with root derepression of the HAK4 Na+ transporter gene. Distinct reactive oxygen species scavengers were also stronger in aoc leaves, along with reduced senescence and chlorophyll catabolism markers. Collectively, our results identify contrasted contributions of JA signaling to different sectors of the salt stress response in rice.

Maize Seedling Growth and Hormone Response Assays Using the Rolled Towel Method

Root system architecture is a critical factor in maize health and stress resilience. Determining the genetic and environmental factors that shape maize root system architecture is an active research area. However, the ability to phenotype juvenile root systems is hindered by the use of field-grown and soil-based systems. An alternative to soil- and field-based growing conditions for maize seedlings is a controlled environment with a soil-free medium, which can facilitate root system phenotyping. Here, we describe how to grow maize under soil-free conditions for up to 12 days to facilitate root phenotyping. Maize seeds are sterilized and planted on specialized seed germination paper to minimize fungal contamination and ensure synchronized seedling growth, followed by imaging at the desired time point. The root images are then analyzed to quantify traits of interest, such as primary root length, lateral root density, seminal root length, and seminal root number. In addition, juvenile shoot traits can be quantified using manual annotation methods. We also outline the steps for performing rigorous hormone response assays for four classical phytohormones: auxin, brassinosteroid, cytokinin, and jasmonic acid. This protocol can be rapidly scaled up and is compatible with genetic screens and sample collection for downstream molecular analyses such as transcriptomics and proteomics. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Maize seedling rolled towel assay and phenotyping Basic Protocol 2: Maize seedling hormone response assays using the rolled towel assay.

Comparative Transcriptomics Reveals the Molecular Mechanism of the Parental Lines of Maize Hybrid An'nong876 in Response to Salt Stress

Maize (Zea mays L.) is an essential food crop worldwide, but it is highly susceptible to salt stress, especially at the seedling stage. In this study, we conducted physiological and comparative transcriptome analyses of seedlings of maize inbred lines An’nong876 paternal (cmh15) and An’nong876 maternal (CM37) under salt stress. The cmh15 seedlings were more salt-tolerant and had higher relative water content, lower electrolyte leakage, and lower malondialdehyde levels in the leaves than CM37. We identified 2559 upregulated and 1770 downregulated genes between salt-treated CM37 and the controls, and 2757 upregulated and 2634 downregulated genes between salt-treated cmh15 and the controls by RNA sequencing analysis. Gene ontology functional enrichment analysis of the differentially expressed genes showed that photosynthesis-related and oxidation-reduction processes were deeply involved in the responses of cmh15 and CM37 to salt stress. We also found differences in the hormone signaling pathway transduction and regulation patterns of transcription factors encoded by the differentially expressed genes in both cmh15 and CM37 under salt stress. Together, our findings provide insights into the molecular networks that mediate salt stress tolerance of maize at the seedling stage.

Regulatory Mechanism of the Constitutive Photomorphogenesis 9 Signalosome Complex in Response to Abiotic Stress in Plants

The constitutive photomorphogenesis 9 (COP9) signalosome (CSN) is a highly conserved protein complex that regulates signaling pathways in plants under abiotic stress. We discuss the potential molecular mechanisms of CSN under abiotic stress, including oxidative stress with reactive oxygen species signaling, salt stress with jasmonic acid, gibberellic acid, and abscisic acid signaling, high-temperature stress with auxin signaling, and optical radiation with DNA damage and repair response. We conclude that CSN likely participates in affecting antioxidant biosynthesis and hormone signaling by targeting receptors, kinases, and transcription factors in response to abiotic stress, which potentially provides valuable information for engineering stress-tolerant crops.

Comparative transcriptomic and metabolic profiling provides insight into the mechanism by which the autophagy inhibitor 3-MA enhances salt stress sensitivity in wheat seedlings

BACKGROUND

Salt stress hinders plant growth and production around the world. Autophagy induced by salt stress helps plants improve their adaptability to salt stress. However, the underlying mechanism behind this adaptability remains unclear. To obtain deeper insight into this phenomenon, combined metabolomics and transcriptomics analyses were used to explore the coexpression of differentially expressed-metabolite (DEM) and gene (DEG) between control and salt-stressed wheat roots and leaves in the presence or absence of the added autophagy inhibitor 3-methyladenine (3-MA).

RESULTS

The results indicated that 3-MA addition inhibited autophagy, increased ROS accumulation, damaged photosynthesis apparatus and impaired the tolerance of wheat seedlings to NaCl stress. A total of 14,759 DEGs and 554 DEMs in roots and leaves of wheat seedlings were induced by salt stress. DEGs were predominantly enriched in cellular amino acid catabolic process, response to external biotic stimulus, regulation of the response to salt stress, reactive oxygen species (ROS) biosynthetic process, regulation of response to osmotic stress, ect. The DEMs were mostly associated with amino acid metabolism, carbohydrate metabolism, phenylalanine metabolism, carbapenem biosynthesis, and pantothenate and CoA biosynthesis. Further analysis identified some critical genes (gene involved in the oxidative stress response, gene encoding transcription factor (TF) and gene involved in the synthesis of metabolite such as alanine, asparagine, aspartate, glutamate, glutamine, 4-aminobutyric acid, abscisic acid, jasmonic acid, ect.) that potentially participated in a complex regulatory network in the wheat response to NaCl stress. The expression of the upregulated DEGs and DEMs were higher, and the expression of the down-regulated DEGs and DEMs was lower in 3-MA-treated plants under NaCl treatment.

CONCLUSION

3-MA enhanced the salt stress sensitivity of wheat seedlings by inhibiting the activity of the roots and leaves, inhibiting autophagy in the roots and leaves, increasing the content of both H₂O₂ and O₂•-, damaged photosynthesis apparatus and changing the transcriptome and metabolome of salt-stressed wheat seedlings.

Hormonal crosstalk in regulating salinity stress tolerance in graminaceous crops

Soil salinity is one of the major threats that pose challenges to global cereal productivity and food security. Cereals have evolved sophisticated mechanisms to circumvent stress at morpho-physiological, biochemical, and molecular levels. Salt stress cues are perceived by the roots, which trigger the underlying signaling pathways that involve phytohormones. Each phytohormone triggers a specific signaling pathway integrated in a complex manner to produce antagonistic, synergistic, and additive responses. Phytohormones induce salt-responsive signaling pathways to modulate various physiological and anatomical mechanisms, including cell wall repair, apoplastic pH regulation, ion homeostasis, root hair formation, chlorophyll content, and leaf morphology. Exogenous applications of phytohormones moderate the adverse effects of salinity and improve growth. Understanding the complex hormonal crosstalk in cereals under salt stress will advance the knowledge about cooperation or antagonistic mechanisms among hormones and their role in developing salt-tolerant cereals to enhance the productivity of saline agricultural land. In this context, the present review focuses on the mechanisms of hormonal crosstalk that mediate the salt stress response and adaptation in graminaceous crops.

Analysis of Phytohormone Signal Transduction in Sophora alopecuroides under Salt Stress

Salt stress seriously restricts crop yield and quality, leading to an urgent need to understand its effects on plants and the mechanism of plant responses. Although phytohormones are crucial for plant responses to salt stress, the role of phytohormone signal transduction in the salt stress responses of stress-resistant species such as Sophora alopecuroides has not been reported. Herein, we combined transcriptome and metabolome analyses to evaluate expression changes of key genes and metabolites associated with plant hormone signal transduction in S. alopecuroides roots under salt stress for 0 h to 72 h. Auxin, cytokinin, brassinosteroid, and gibberellin signals were predominantly involved in regulating S. alopecuroides growth and recovery under salt stress. Ethylene and jasmonic acid signals may negatively regulate the response of S. alopecuroides to salt stress. Abscisic acid and salicylic acid are significantly upregulated under salt stress, and their signals may positively regulate the plant response to salt stress. Additionally, salicylic acid (SA) might regulate the balance between plant growth and resistance by preventing reduction in growth-promoting hormones and maintaining high levels of abscisic acid (ABA). This study provides insight into the mechanism of salt stress response in S. alopecuroides and the corresponding role of plant hormones, which is beneficial for crop resistance breeding.

How Plant Hormones Mediate Salt Stress Responses

Salt stress is one of the major environmental stresses limiting plant growth and productivity. To adapt to salt stress, plants have developed various strategies to integrate exogenous salinity stress signals with endogenous developmental cues to optimize the balance of growth and stress responses. Accumulating evidence indicates that phytohormones, besides controlling plant growth and development under normal conditions, also mediate various environmental stresses, including salt stress, and thus regulate plant growth adaptation. In this review, we mainly discuss and summarize how plant hormones mediate salinity signals to regulate plant growth adaptation. We also highlight how, in response to salt stress, plants build a defense system by orchestrating the synthesis, signaling, and metabolism of various hormones via multiple crosstalks.

Zinc and Copper Enhance Cucumber Tolerance to Fusaric Acid by Mediating Its Distribution and Toxicity and Modifying the Antioxidant System

Fusaric acid (FA), the fungal toxin produced by Fusarium oxysporum, plays a predominant role in the virulence and symptom development of Fusarium wilt disease. As mineral nutrients can be protective agents against Fusarium wilt, hydroponic experiments employing zinc (Zn) and copper (Cu) followed by FA treatment were conducted in a glasshouse. FA exhibited strong phytotoxicity on cucumber plants, which was reversed by the addition of Zn or Cu. Thus, Zn or Cu dramatically reduced the wilt index, alleviated the leaf or root cell membrane injury and mitigated against the FA inhibition of plant growth and photosynthesis. Cucumber plants grown with Zn exhibited decreased FA transportation to shoots and a 17% increase in toxicity mitigation and showed minimal hydrogen peroxide, lipid peroxidation level with the increased of antioxidant enzymes activity in both roots and leaves. Cucumber grown with additional Cu absorbed less FA but showed more toxicity mitigation at 20% compared to with additional Zn and exhibited decreased hydrogen peroxide level and increased antioxidant enzymes activity. Thus, adding Zn or Cu can decrease the toxicity of the FA by affecting the absorption or transportation of the FA in plants and mitigate toxicity possibly through chelation. Zn and Cu modify the antioxidant system to scavenge hydrogen peroxide for suppressing FA induction of oxidative damage. Our experiments could provide a theoretical basis for the direct application of micro-fertilizer as protective agents in farming.