Jasmonates: Mechanisms and functions in abiotic stress tolerance of plants

Cadmium toxicity promotes hormonal imbalance and induces the expression of genes involved in systemic resistances in barley

Cadmium (Cd) is a widely distributed pollutant that adversely affects plants' metabolism and productivity. Phytohormones play a vital role in the acclimation of plants to metal stress. On the other hand, phytohormones trigger systemic resistances, including systemic acquired resistance (SAR) and induced systemic resistance (ISR), in plants in response to biotic interactions. The present study aimed to investigate the possible induction of SAR and ISR pathways in relation to the hormonal alteration of barley seedlings in response to Cd stress. Barley seedlings were exposed to 1.5 mg g-1 Cd in the soil for three days. The nutrient content, oxidative status, phytohormones profile, and expression of genes involved in SAR and ISR pathways of barley seedlings were examined. Cd accumulation resulted in a reduction in the nutrient content of barley seedlings. The specific activity of superoxide dismutase and the hydrogen peroxide content significantly increased in response to Cd toxicity. Abscisic acid, jasmonic acid, and ethylene content increased under Cd exposure. Cd treatment resulted in the upregulation of NPR1, PR3, and PR13 genes in SAR pathways. The transcripts of PAL1 and LOX2.2 genes in the ISR pathway were also significantly increased in response to Cd treatment. These findings suggest that hormonal-activated systemic resistances are involved in the response of barley to Cd stress.

Caffeic Acid O-Methyltransferase Gene Family in Mango (Mangifera indica L.) with Transcriptional Analysis under Biotic and Abiotic Stresses and the Role of MiCOMT1 in Salt Tolerance

Caffeic acid O-methyltransferase (COMT) participates in various physiological activities in plants, such as positive responses to abiotic stresses and the signal transduction of phytohormones. In this study, 18 COMT genes were identified in the chromosome-level reference genome of mango, named MiCOMTs. A phylogenetic tree containing nine groups (I-IX) was constructed based on the amino acid sequences of the 71 COMT proteins from seven species. The phylogenetic tree indicated that the members of the MiCOMTs could be divided into four groups. Quantitative real-time PCR showed that all MiCOMT genes have particularly high expression levels during flowering. The expression levels of MiCOMTs were different under abiotic and biotic stresses, including salt and stimulated drought stresses, ABA and SA treatment, as well as Xanthomonas campestris pv. mangiferaeindicae and Colletotrichum gloeosporioides infection, respectively. Among them, the expression level of MiCOMT1 was significantly up-regulated at 6-72 h after salt and stimulated drought stresses. The results of gene function analysis via the transient overexpression of the MiCOMT1 gene in Nicotiana benthamiana showed that the MiCOMT1 gene can promote the accumulation of ABA and MeJA, and improve the salt tolerance of mango. These results are beneficial to future researchers aiming to understand the biological functions and molecular mechanisms of MiCOMT genes.

Calcium (Ca2+ ) sensors and MYC2 are crucial players during jasmonates-mediated abiotic stress tolerance in plants

Plants evolve stress-specific responses that sense changes in their external environmental conditions and develop various mechanisms for acclimatization and survival. Calcium (Ca2+ ) is an essential stress-sensing secondary messenger in plants. Ca2+ sensors, including calcium-dependent protein kinases (CDPKs), calmodulins (CaMs), CaM-like proteins (CMLs), and calcineurin B-like proteins (CBLs), are involved in jasmonates (JAs) signalling and biosynthesis. Moreover, JAs are phospholipid-derived phytohormones that control plant response to abiotic stresses. The JAs signalling pathway affects hormone-receptor gene transcription by binding to the basic helix-loop-helix (bHLH) transcription factor. MYC2 acts as a master regulator of JAs signalling module assimilated through various genes. The Ca2+ sensor CML regulates MYC2 and is involved in a distinct mechanism mediating JAs signalling during abiotic stresses. This review highlights the pivotal role of the Ca2+ sensors in JAs biosynthesis and MYC2-mediated JAs signalling during abiotic stresses in plants.

A review of plants strategies to resist biotic and abiotic environmental stressors

Plants exposed to a variety of abiotic and biotic stressors including environmental pollution and global warming pose significant threats to biodiversity and ecosystem services. Despite substantial literature documenting how plants adapt to distinct stressors, there still is a lack of knowledge regarding responses to multiple stressors and how these affects growth and development. Exposure of plants to concurrent biotic and abiotic stressors such as cadmium and drought, leads to pronounced inhibition in above ground biomass, imbalance in oxidative homeostasis, nutrient assimilation and stunted root growth, elucidating the synergistic interactions of multiple stressors culminating in adverse physiological outcomes. Impact of elevated heavy metal and water deficit exposure extends beyond growth and development, influencing the biodiversity of the microenvironment including the rhizosphere nutrient profile and microbiome. These findings have significant implications for plant-stress interactions and ecosystem functioning that prompt immediate action in order to eliminate effect of pollution and address global environmental issues to promote sustainable tolerance for multiple stress combinations in plants. Here, we review plant tolerance against stress combinations, highlighting the need for interdisciplinary approaches and advanced technologies, such as omics and molecular tools, to achieve a comprehensive understanding of underlying stress tolerance mechanisms. To accelerate progress towards developing stress-tolerance in plants against multiple environmental stressors, future research in plant stress tolerance should adopt a collaborative approach, involving researchers from multiple disciplines with diverse expertise and resources.

Exogenous phthalanilic acid induces resistance to drought stress in pepper seedlings (Capsicum annuum L.)

Drought stress (DS) is one of the main abiotic negative factors for plants. Phthalanilic acid (PPA), as a plant growth regulator, can promote the growth and development of crops. In order to evaluate the ideal application concentration and frequency of PPA-induced drought resistance in pepper (Capsicum annuum) seedlings, the concentration of PPA was 133.3 mg·L-1; 200.0 mg·L-1; 266.7 mg·L-1, and some key indicators were investigated, including leaf wilting index (LWI), relative water content (RWC), and malondialdehyde (MDA). We found that the LWI and RWC in the PPA-applied pepper leaves under light drought stress (LDS) and moderate drought stress (MDS) were all elevated, while MDA contents were decreased. To better understand how PPA makes pepper drought resistant, we examined the photosynthetic characteristics, growth parameters, antioxidant activities, and osmotic substances in pepper seedlings treated twice with PPA at a concentration of 133.3 mg·L-1 under LDS, MDS, and severe drought stress (SDS). Results showed that PPA increased the chlorophyll, plant height, stem diameter, root-shoot ratio, and seedling index of pepper leaves under LDS, MDS, and SDS. The net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci), transpiration rates (Tr), and water-use efficiency (WUE) in the PPA-treated pepper leaves under LDS and MDS were improved, while their stomatal limitation (Ls) were reduced. PPA also boosted the activities of enzymatic antioxidants (superoxide dismutase, catalase, and peroxidase), as well as enhanced the accumulation of osmotic substances such as soluble sugar, soluble protein, and free proline in pepper leaves under LDS, MDS, and SDS. Thus, PPA can alleviate the growth inhibition and damage to pepper seedlings caused by DS, and the PPA-mediated efficacy may be associated with the improvement in PPA-mediated antioxidant activities, Pn, and accumulation of osmotic substances.

Effect of jasmonic acid on the phytoremediation of dinitrophenol from wastewater by Solanum nigrum L. and Atriplex lentiformis (Torr.) S. Watson

Phytoremediation is one of the best methods for cleaning up natural resources like water because plants are eco-friendly and safe for the ecosystem. Hyperaccumulators, e.g., Solanum nigrum L. and Atriplex lentiformis (Torr.) S. Watson, have been used to remove toxic metals from soil and water through phytoremediation techniques, but it is unknown if they can remove hazardous chemicals such as dinitrophenol (DNP), from wastewater. A hydroponic experiment was conducted to study the efficiency of S. nigrum and A. lentiformis in removing DNP from wastewater. Jasmonic acid (JAC) was applied to the tested plants in two doses, 0.25 and 0.50 mmol, in an effort to better understand how it affects phytoremediation effectiveness. The growth of S. nigrum and A. lentiformis improved significantly (p < 0.05) by the foliar application of JAC. The applications of JAC1 and JAC2 significantly (p < 0.05) increased nutrient uptake and chlorophyll concentrations in S. nigrum and A. lentiformis plants. The foliar spraying of S. nigrum and A. lentiformis with JAC significantly (p < 0.05) increased the antioxidant enzymes activity, i.e., SOD and POD. The levels of osmoregulatory substances like proline and carbohydrates significantly (p < 0.05) increased after JAC was sprayed on S. nigrum and A. lentiformis plants. In the case of S. nigrum, the efficiency of DNP removal varied between 53 and 69%, with an average of 63%, while in the case of A. lentiformis, it varied between 47 and 62%, with an average of 56%. The removal efficiency of DNP reached 67 and 69% when S. nigrum was sprayed with JAC1 and JAC2. When JAC1 and JAC2 were sprayed on A. lentiformis, DNP removal efficiency rose from 47 to 60 and from 47 to 62%, respectively. S. nigrum and A. lentiformis plants can be grown normally and survive in dinitrophenol-contaminated water without showing any toxic symptoms. S. nigrum and A. lentiformis have a powerful antioxidant system and the ability to produce vital compounds that alleviate the stress caused by DNP toxicity. The findings are crucial for cleaning up polluted water and protecting the ecosystem's health from dangerous pollutants.

Effect of Methyl Jasmonate on the Gene Expression, Encoding Non-Protein Thiol Enzymes in Wheat under Cadmium

The effect of the phytohormone methyl jasmonate (MJ) on the expression of the TaGS1 and TaPCS1 genes encoding glutathione synthetase and phytochelatin synthase, respectively, which are key enzymes in the synthesis of glutathione and phytochelatins in wheat (cv. Moskovskaya 39), was studied. It was shown for the first time that pretreatment of plants by exogenous MJ (1 μM) leads to an increase in the accumulation of transcripts of the TaGS1 and TaPCS1 genes in leaves without cadmium effect. When cadmium (CdSO₄, 100 μM) was added into the nutrient solution, the transcript level of the TaGS1 gene in the plants pretreated by MJ increased (compared to the untreated plants), whereas the transcript level of TaPCS1 remained unaffected. The pretreatment of plants with MJ leads to a lower accumulation of cadmium in the roots and leaves of wheat. At the same time, MJ had no effect on the linear growth parameters of plants, but had a positive effect on the accumulation of biomass under cadmium. It was assumed that MJ is involved in plant tolerance to cadmium by increasing the expression of the TaGS1 and TaPCS1 genes and, as a result, enhancing the synthesis of chelating compounds, as well as by reducing the supply of metal ions to plants.

Does Methyl Jasmonate Effectively Protect Plants under Heavy Metal Contamination? Fatty Acid Content in Wheat Leaves Exposed to Cadmium with or without Exogenous Methyl Jasmonate Application

The effect of methyl jasmonate (MJ) (1 µM) on wheat (Triticum aestivum L. cv. Moskovskaya 39), seedlings and the fatty acid (FA) content of leaves under optimal and cadmium (Cd) (100 µM) stress conditions wasinvestigated. Height and biomass accumulation was studied traditionally; the netphotosynthesis rate (P_n) was studied using a photosynthesis system, FAs'profile-GS-MS. No effect on the height and P_n rate of the MJ pre-treatment wheat at optimum growth conditions was found. MJ pre-treatment led to a decrease in the total amount of saturated (about 11%) and unsaturated (about 17%) identified FAs, except α-linoleic FA (ALA), which is probably associated with its involvement in energy-dependent processes. Under Cd impact, the MJ-treated plants had a higher biomass accumulation and P_n rate compared to untreated seedlings. Both MJ and Cd caused stress-induced elevation of palmitic acid (PA) versus an absence of myristic acid (MA), which is used for elongation. It is suggested that PA participates in alternative adaptation mechanisms (not only as a constituent of the lipid bilayer of biomembrane) of plants under stress. Overall, the dynamics of FAs showed an increase in the saturated FA that is important in the packing of the biomembrane. It is supposed that the positive effect of MJ is associated with lower Cd content in plants and a higher ALA content in leaves.

Interactions of Polyamines and Phytohormones in Plant Response to Abiotic Stress

Numerous environmental conditions negatively affect plant production. Abiotic stresses, such as salinity, drought, temperature, and heavy metals, cause damage at the physiological, biochemical, and molecular level, and limit plant growth, development, and survival. Studies have indicated that small amine compounds, polyamines (PAs), play a key role in plant tolerance to various abiotic stresses. Pharmacological and molecular studies, as well as research using genetic and transgenic approaches, have revealed the favorable effects of PAs on growth, ion homeostasis, water maintenance, photosynthesis, reactive oxygen species (ROS) accumulation, and antioxidant systems in many plant species under abiotic stress. PAs display a multitrack action: regulating the expression of stress response genes and the activity of ion channels; improving the stability of membranes, DNA, and other biomolecules; and interacting with signaling molecules and plant hormones. In recent years the number of reports indicating crosstalk between PAs and phytohormones in plant response to abiotic stresses has increased. Interestingly, some plant hormones, previously known as plant growth regulators, can also participate in plant response to abiotic stresses. Therefore, the main goal of this review is to summarize the most significant results that represent the interactions between PAs and plant hormones, such as abscisic acid, brassinosteroids, ethylene, jasmonates, and gibberellins, in plants under abiotic stress. The future perspectives for research focusing on the crosstalk between PAs and plant hormones were also discussed.

Transcriptome Analysis of Endogenous Hormone Response Mechanism in Roots of Styrax tonkinensis Under Waterlogging

As a promising oil species, Styrax tonkinensis has great potential as a biofuel due to an excellent fatty acid composition. However, frequent flooding caused by global warming and the low tolerance of the species to waterlogging largely halted its expansion in waterlogged areas. To explore endogenous hormones and phytohormone-related molecular response mechanism of S. tonkinensis under waterlogging, we determined 1-aminocyclopropane-1-carboxylic acid (ACC) and three phytohormone content (ABA, abscisic acid; SA, salicylic acid; IAA, indole-3-acetic acid) and analyzed the transcriptome of its seedlings under waterlogged condition of 3-5 cm. The sample collecting time was 0, 9, 24, and 72 h, respectively. It was concluded that ACC presented an upward trend, but other plant hormones showed a downward trend from 0 to 72 h under waterlogging stress. A total of 84,601 unigenes were assembled with a total length of 81,389,823 bp through transcriptome analysis. The GO enrichment analysis of total differentially expressed genes (DEGs) revealed that 4,637 DEGs, 8,238 DEGs, and 7,146 DEGs were assigned into three main GO functional categories in 9 vs. 0 h, 24 vs. 0 h, and 72 vs. 0 h, respectively. We also discovered several DEGs involved in phytohormone synthesis pathway and plant hormone signaling pathway. It was concluded that the decreased transcription of PYL resulted in the weak ABA signal transduction pathway. Moreover, decreased SA content caused by the low-expressed PAL might impact the resistance of S. tonkinensis seedlings under waterlogging stress. Our research may provide a scientific basis for the understanding of the endogenous hormone response mechanism of S. tonkinensis to waterlogging and lay a foundation for further exploration of the waterlogging defect resistance genes of S. tonkinensis and improving its resistance to waterlogging stress.

Overcoming Reproductive Compromise Under Heat Stress in Wheat: Physiological and Genetic Regulation, and Breeding Strategy

The reproductive compromise under heat stress is a major obstacle to achieve high grain yield and quality in wheat worldwide. Securing reproductive success is the key solution to sustain wheat productivity by understanding the physiological mechanism and molecular basis in conferring heat tolerance and utilizing the candidate gene resources for breeding. In this study, we examined the performance on both carbon supply source (as leaf photosynthetic rate) and carbon sink intake (as grain yields and quality) in wheat under heat stress varying with timing, duration, and intensity, and we further surveyed physiological processes from source to sink and the associated genetic basis in regulating reproductive thermotolerance; in addition, we summarized the quantitative trait loci (QTLs) and genes identified for heat stress tolerance associated with reproductive stages. Discovery of novel genes for thermotolerance is made more efficient via the combination of transcriptomics, proteomics, metabolomics, and phenomics. Gene editing of specific genes for novel varieties governing heat tolerance is also discussed.

Recent Trends in Microbial Approaches for Soil Desalination

Soil salinization has become a major problem for agriculture worldwide, especially because this phenomenon is continuously expanding in different regions of the world. Salinity is a complex mechanism, and in the soil ecosystem, it affects both microorganisms and plants, some of which have developed efficient strategies to alleviate salt stress conditions. Currently, various methods can be used to reduce the negative effects of this problem. However, the use of biological methods, such as plant-growth-promoting bacteria (PGPB), phytoremediation, and amendment, seems to be very advantageous and promising as a remedy for sustainable and ecological agriculture. Other approaches aim to combine different techniques, as well as the utilization of genetic engineering methods. These techniques alone or combined can effectively contribute to the development of sustainable and eco-friendly agriculture.

Salt Stress in Plants and Mitigation Approaches

Salinization of soils and freshwater resources by natural processes and/or human activities has become an increasing issue that affects environmental services and socioeconomic relations. In addition, salinization jeopardizes agroecosystems, inducing salt stress in most cultivated plants (nutrient deficiency, pH and oxidative stress, biomass reduction), and directly affects the quality and quantity of food production. Depending on the type of salt/stress (alkaline or pH-neutral), specific approaches and solutions should be applied to ameliorate the situation on-site. Various agro-hydrotechnical (soil and water conservation, reduced tillage, mulching, rainwater harvesting, irrigation and drainage, control of seawater intrusion), biological (agroforestry, multi-cropping, cultivation of salt-resistant species, bacterial inoculation, promotion of mycorrhiza, grafting with salt-resistant rootstocks), chemical (application of organic and mineral amendments, phytohormones), bio-ecological (breeding, desalination, application of nano-based products, seed biopriming), and/or institutional solutions (salinity monitoring, integrated national and regional strategies) are very effective against salinity/salt stress and numerous other constraints. Advances in computer science (artificial intelligence, machine learning) provide rapid predictions of salinization processes from the field to the global scale, under numerous scenarios, including climate change. Thus, these results represent a comprehensive outcome and tool for a multidisciplinary approach to protect and control salinization, minimizing damages caused by salt stress.

Elicitation of isoflavonoids in Colombian edible legume plants with jasmonates and structurally related compounds

Common bean (Phaseolus vulgaris L.), soybean (Glycine max L.) and mung bean (Vigna radiata L. Wilczek) seedlings were treated with methyl jasmonate (MeJA); then, dose-response and time-course experiments were carried out. Isoflavonoid composition was evaluated by high performance liquid chromatography. As a result of MeJA induction, all leguminous plants increase the amount of isoflavonoids, at levels that depend on the concentration of the elicitor and the time after induction. However, the application of MeJA in concentrations higher than 2.22 mM showed deleterious effects on seedlings and strong decreases in the concentration of isoflavonoids. In addition, a series of compounds structurally related to MeJA, such as jasmonic acid, cis-jasmone, coronatine, and indanoyl derivatives, were evaluated as elicitors. The results show that coronatine and the indanoyl-amino acids conjugates displayed a significant elicitor effect of isoflavonoids in common bean (cvs. Cargamanto Mocho and Corpoica LAS 106) and soybean (cv. Soyica P-34) seedlings, even higher than that found with the recognized elicitors, benzo (1,2,3) thiadiazole-7-carbothioic acid S-methyl ester (acibenzolar S-methyl) and benzo-(1,2,3) thiadiazole-7-carbothioic acid (acibenzolar acid). Leguminous plants can be treated with jasmonates and indanoyl derivatives to increase levels of bioactive isoflavonoids and consequently improve biological and functional properties and resistance against pests.

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The accumulation of isoflavonoids in edible legume seedlings treated with jasmonates and structurally related compounds was analyzed.

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Time-course and dose-response experiments were performed using methyl jasmonate as elicitor.

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The application of jasmonates and structurally related compounds increased the concentration of bioactive isoflavonoids.

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The amount of isoflavonoids depended on the cultivar, the concentration and structure of the elicitor, and the post-induction time.

Beneficial Microbes and Molecules for Mitigation of Soil Salinity in Brassica Species: A Review

Salt stress results from excessive salt accumulation in the soil can lead to a reduction in plant growth and yield. Due to climate change, in the future climatic pressures, changed precipitation cycles and increased temperature will increase the pressures on agriculture, including increasing severity of salt stress. Brassica species contains oilseed and vegetable crops with great economic importance. Advances in understanding the mechanisms of salt stress in Brassica plants have enabled the development of approaches to better induce plant defense mechanisms at the time of their occurrence through the use of beneficial microorganisms or molecules. Both endophytic and rhizospheric microbes contribute to the mitigation of abiotic stresses in Brassica plants by promoting the growth of their host under stress conditions. In this review we summarized so far reported microorganisms with beneficial effects on Brassica plants and their mode of action. Another approach in mitigating the harmful effect of soil salinity may involve the application of different molecules that are involved in the stress response of Brassica plants. We reviewed and summarized their potential mode of action, methods of application and pointed out further research directions.

Biochemical and Metabolic Plant Responses toward Polycyclic Aromatic Hydrocarbons and Heavy Metals Present in Atmospheric Pollution

Heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) are toxic components of atmospheric particles. These pollutants induce a wide variety of responses in plants, leading to tolerance or toxicity. Their effects on plants depend on many different environmental conditions, not only the type and concentration of contaminant, temperature or soil pH, but also on the physiological or genetic status of the plant. The main detoxification process in plants is the accumulation of the contaminant in vacuoles or cell walls. PAHs are normally transformed by enzymatic plant machinery prior to conjugation and immobilization; heavy metals are frequently chelated by some molecules, with glutathione, phytochelatins and metallothioneins being the main players in heavy metal detoxification. Besides these detoxification mechanisms, the presence of contaminants leads to the production of the reactive oxygen species (ROS) and the dynamic of ROS production and detoxification renders different outcomes in different scenarios, from cellular death to the induction of stress resistances. ROS responses have been extensively studied; the complexity of the ROS response and the subsequent cascade of effects on phytohormones and metabolic changes, which depend on local concentrations in different organelles and on the lifetime of each ROS species, allow the plant to modulate its responses to different environmental clues. Basic knowledge of plant responses toward pollutants is key to improving phytoremediation technologies.

Therapeutic Potential of Jasmonic Acid and Its Derivatives

A modern method of therapeutic use of natural compounds that would protect the body are jasmonates. The main representatives of jasmonate compounds include jasmonic acid and its derivatives, mainly methyl jasmonate. Extracts from plants rich in jasmonic compounds show a broad spectrum of activity, i.e., anti-cancer, anti-inflammatory and cosmetic. Studies of the biological activity of jasmonic acid and its derivatives in mammals are based on their structural similarity to prostaglandins and the compounds can be used as natural therapeutics for inflammation. Jasmonates also constitute a potential group of anti-cancer drugs that can be used alone or in combination with other known chemotherapeutic agents. Moreover, due to their ability to stimulate exfoliation of the epidermis, remove discoloration, regulate the function of the sebaceous glands and reduce the visible signs of aging, they are considered for possible use in cosmetics and dermatology. The paper presents a review of literature data on the biological activity of jasmonates that may be helpful in treatment and prevention.

Exogenous Methyl Jasmonate Improves Cold Tolerance with Parallel Induction of Two Cold-Regulated (COR) Genes Expression in Triticum aestivum L

Methyl jasmonate (MJ) is an important plant growth regulator that plays a key role in tolerance to biotic and abiotic stresses. In this research, the effects of exogenous MJ on cold tolerance, photosynthesis, activity and gene expression of antioxidant enzymes, proline accumulation, and expression of cold-regulated (COR) genes in wheat seedlings under low temperature (4 °C) were investigated. Exogenous MJ treatment (1 µM) promoted wheat cold tolerance before and during cold exposure. Low temperature significantly decreased photosynthetic parameters, whereas MJ application led to their partial recovery under cold exposure. Hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels increased in response to low temperature, and this was counteracted by MJ application. Exogenous MJ significantly enhanced the activities of antioxidant enzymes and upregulated the expression of MnSOD and CAT during cold exposure. MJ application also led to enhanced proline content before 4 °C exposure, whereas the P5CS gene expression was upregulated by MJ's presence at both normal (22 °C) and low (4 °C) temperatures. It was also shown that MJ tended to upregulate the expression of the COR genes WCS19 and WCS120 genes. We conclude that exogenous MJ can alleviate the negative effect of cold stress thus increasing wheat cold tolerance.

Physiological and transcriptional changes provide insights into the effect of root waterlogging on the aboveground part of Pterocarya stenoptera

Pterocarya stenoptera is a tree species that occurs along rivers and has high tolerance to waterlogging. Identification of waterlogging response genes in the aboveground part of P. stenoptera will increase understanding of tolerance mechanisms under root waterlogging conditions. In this study, we employed four physiological indicators and comparative transcriptome sequencing to investigate the waterlogging tolerance mechanism in P. stenoptera. The physiological results showed that the aboveground part of P. stenoptera was not obviously affected by waterlogging. P. stenoptera enhanced waterlogging tolerance by increasing the synthesis of alpha-Linolenic acids and flavonoids and activating the jasmonic acid, ethylene, and auxin signaling pathways. Our results confirmed our hypothesis that P. stenoptera, a species that is widely distributed along rivers, has evolved a range of mechanisms in response to waterlogging. Our research will provide new insights for understanding the tolerance mechanism of species to waterlogging.

Environmental salinization processes: Detection, implications & solutions

A great portion of Earth's freshwater and land resources are salt-affected and thus have restricted use or may become unsuitable for most human activities. Some of the recent scenarios warn that environmental salinization processes will continue to be exacerbated due to global climate change. The most relevant implications and side-effects in ecosystems under excessive salinity are destructive and long lasting (e.g. soil dispersion, water/soil hypersalinity, desertification, ruined biodiversity), often with non-feasible on site remediation, especially at larger scales. Agro-ecosystems are very sensitive to salinization; after a certain threshold is reached, yields and food quality start to deteriorate sharply. Additionally, salinity often coincides with numerous other environmental constrains (drought, waterlogging, pollution, acidity, nutrient deficiency, etc.) that progressively aggravate the threat to food security and general ecosystem resilience. Some well-proven, widely-used and cost-effective traditional ameliorative strategies (e.g. conservation agriculture, application of natural conditioners) help against salinity and other constraints, especially in developing countries. Remotely-sensed and integrated data of salt-affected areas combined with in situ and lab-based observations have never been so easy and rapid to acquire, precise and applicable on huge scales, representing a valuable tool for policy-makers and other stakeholders in implementing targeted measures to control and prevent ecosystem degradation (top-to-bottom approach). Continued progress in biotechnology and ecoengineering offers some of the most advanced and effective solutions against salinity (e.g. nanomaterials, marker-assisted breeding, genome editing, plant-microbial associations), albeit many knowledge gaps and ethical frontiers remain to be overcome before a successful transfer of these potential solutions to the industrial-scale food production can be effective.

Response of phytohormone mediated plant homeodomain (PHD) family to abiotic stress in upland cotton (Gossypium hirsutum spp.)

BACKGROUND

The sequencing and annotations of cotton genomes provide powerful theoretical support to unravel more physiological and functional information. Plant homeodomain (PHD) protein family has been reported to be involved in regulating various biological processes in plants. However, their functional studies have not yet been carried out in cotton.

RESULTS

In this study, 108, 55, and 52 PHD genes were identified in G. hirsutum, G. raimondii, and G. arboreum, respectively. A total of 297 PHD genes from three cotton species, Arabidopsis, and rice were divided into five groups. We performed chromosomal location, phylogenetic relationship, gene structure, and conserved domain analysis for GhPHD genes. GhPHD genes were unevenly distributed on each chromosome. However, more GhPHD genes were distributed on At_05, Dt_05, and At_07 chromosomes. GhPHD proteins depicted conserved domains, and GhPHD genes exhibiting similar gene structure were clustered together. Further, whole genome duplication (WGD) analysis indicated that purification selection greatly contributed to the functional maintenance of GhPHD gene family. Expression pattern analysis based on RNA-seq data showed that most GhPHD genes showed clear tissue-specific spatiotemporal expression patterns elucidating the multiple functions of GhPHDs in plant growth and development. Moreover, analysis of cis-acting elements revealed that GhPHDs may respond to a variety of abiotic and phytohormonal stresses. In this regard, some GhPHD genes showed good response against abiotic and phytohormonal stresses. Additionally, co-expression network analysis indicated that GhPHDs are essential for plant growth and development, while GhPHD genes response against abiotic and phytohormonal stresses may help to improve plant tolerance in adverse environmental conditions.

CONCLUSION

This study will provide useful information to facilitate further research related to the vital roles of GhPHD gene family in plant growth and development.

Jasmonates Alleviate the Harm of High-Temperature Stress During Anthesis to Stigma Vitality of Photothermosensitive Genetic Male Sterile Rice Lines

Using photothermosensitive genic male sterile (PTSGMS) rice (Oryza sativa L.) lines to produce hybrids can obtain great heterosis. However, PTSGMS rice lines exhibit low stigma vitality when high-temperature (HT) stress happens during anthesis. Jasmonates (JAs) are novel phytohormones and play vital roles in mediating biotic and abiotic stresses. Little is known, however, if and how JAs could alleviate the harm of HT stress during anthesis to the stigma vitality of PTSGMS lines. This study investigated the question. Two PTSGMS lines and one restorer line of rice were pot-grown and subjected to normal temperature and HT stress during anthesis. The stigma exertion rate, sigma fresh weight, stigma area, contents of JAs, hydrogen peroxide (H₂O₂), and ascorbic acid (AsA), activity of catalase in stigmas, and the number of pollens germinated on the stigma of PTSGMS lines were determined. The results showed that a rice line with higher JAs content in the stigma under HT stress showed lower H₂O₂ content, higher AsA content and catalase activity in stigmas, larger stigma area, heavier stigma fresh weight, more pollens germinated on the stigma, and higher fertilization and seed-setting and rates. Applying methyl JAs during anthesis to rice panicles decreased the accumulation of reactive oxygen species and enhanced stigma vitality, thereby increasing fertilization and seed-setting rates of the hybrids of PTSGMS rice lines under HT stress. The results demonstrate that JAs attenuate the injury of HT stress to the stigma vitality of PTSGMS rice lines through enhancing antioxidant ability.

Growth-promoting bacteria and natural regulators mitigate salt toxicity and improve rapeseed plant performance

Salinity is a major environmental stress that limits plant production and portraits a critical challenge to food security in the world. In this research, the impacts of plant growth-promoting bacteria (Pseudomonas RS-198 and Azospirillum brasilense RS-SP7) and foliar application of plant hormones (salicylic acid 1 mM and jasmonic acid 0.5 mM) on alleviating the harmful effects of salt stress in rapeseed plants (Brassica napus cv. okapi) were examined under greenhouse condition. Salt stress diminished rapeseed biomass, leaf area, water content, nitrogen, phosphorus, potassium, calcium, magnesium, and chlorophyll content, while it increased sodium content, endogenous salicylic and jasmonic acids, osmolyte production, H₂O₂ and O₂^•- generations, TBARS content, and antioxidant enzyme activities. Plant growth, nutrient content, leaf expansion, osmolyte production, and antioxidant enzyme activities were increased, but oxidative and osmotic stress indicators were decreased by bacteria inoculation + salicylic acid under salt stress. Antioxidant enzyme activities were amplified by jasmonic acid treatments under salt stress, although rapeseed growth was not generally affected by jasmonic acid. Bacterial + hormonal treatments were superior to individual treatments in reducing detrimental effects of salt stress. The best treatment in rectifying rapeseed growth under salt stress was combination of Pseudomonas and salicylic acid. This combination attenuated destructive salinity properties and subsequently amended rapeseed growth via enhancing endogenous salicylic acid content and some essential nutrients such as potassium, phosphorus, and magnesium.

Genome-wide expression analysis suggests glutaredoxin genes response to various stresses in cotton

Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species (ROS) and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Glutaredoxins (GRXs) are ubiquitous oxidoreductase enzymes involved in diverse cellular processes and play a key role in oxidative stress responsive mechanisms. This study was aimed to explore the structure-function relationship and to provide a framework for functional validation and biochemical characterization of various GRX members. In this study, our analysis revealed the presence of 127 genes encoding GRX proteins in G. hirsutum. A total of 758 genes from two typical monocot and nine dicot species were naturally divided into four classes based on phylogenetic analysis. The classification was supported with organization of conserved protein motifs and sequence logos comparison between cotton, rice and Arabidopsis. Cotton GRX gene family has underwent strong purifying selection with limited functional divergence. A good collinearity was observed in the synteny analysis of four Gossypium species. Majority of cotton GRXs were influenced by various phytohormones and abiotic stress conditions during expression analysis, suggesting an important role of GRX proteins in response to oxidative stress. Cis-regulatory elements, gene enrichments and co-expression network analysis also support their predicted role against various abiotic stresses. Whole genome and segmental duplication were determined to be the two major impetuses for the expansion of gene numbers during the evolution. The identification of GRX genes showing differential expression in specific tissues or in response to environmental stimuli provides a new avenue for in-depth characterization of selected genes of importance. This study will further broaden our insights into the evolution and functional elucidation of GRX gene family in cotton.

Plant susceptibility to ozone: A tower of Babel?

In a world with climate change and environmental pollution, modern Biology is concerned with organismic susceptibility. At the same time, policy and decision makers seek information about organismic susceptibility. Therefore, information about organismic susceptibility may have far-reaching implications to the entire biosphere that can extend to several forthcoming generations. Here, we review a sample of approximately 200 published peer-reviewed articles dealing with plant response to ground-level ozone to understand how the information about susceptibility is communicated. A fuzzy and often incorrect terminology was used to describe the responsiveness of plants to ozone. Susceptibility was classified too arbitrarily and this was reflected to the approximately 50 descriptive words that were used to characterize susceptibility. The classification of susceptibility was commonly based on calculated probability (p) value. This practice is inappropriate as p values do not provide any basis for effect or susceptibility magnitude. To bridge the gap between science and policy decision making, classification of susceptibility should be done using alternative approaches, such as effect size estimates in conjunction with multivariate ordination statistics.

Mechanisms of Waterlogging Tolerance in Plants: Research Progress and Prospects

Waterlogging is one of the main abiotic stresses suffered by plants. Inhibition of aerobic respiration during waterlogging limits energy metabolism and restricts growth and a wide range of developmental processes, from seed germination to vegetative growth and further reproductive growth. Plants respond to waterlogging stress by regulating their morphological structure, energy metabolism, endogenous hormone biosynthesis, and signaling processes. In this updated review, we systematically summarize the changes in morphological structure, photosynthesis, respiration, reactive oxygen species damage, plant hormone synthesis, and signaling cascades after plants were subjected to waterlogging stress. Finally, we propose future challenges and research directions in this field.

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

Jasmonates (JAs) together with jasmonic acid and its offshoots are lipid-derived endogenous hormones that play key roles in both developmental processes and different defense responses in plants. JAs have been studied intensively in the past decades for their substantial roles in plant defense comebacks against diverse environmental stresses among model plants. However, the role of this phytohormone has been poorly investigated in the monocotyledonous species against abiotic stresses. In this study, a JA biosynthesis mutant opr7opr8 was used for the investigation of JA roles in the salt stress responses of maize seedlings, whose roots were exposed to 0 to 300 mM NaCl. Foliar stomatal observation showed that opr7opr8 had a larger stomatal aperture than wild type (WT) (B73) under salinity stress, indicating that JA positively regulates guard cell movement under salt stress. The results regarding chlorophyll content and leaf senescence showed that opr7opr8 exhibited delayed leaf senescence under salt stress as compared to WT, indicating that JA plays a role in salt-inducing cell death and subsequent leaf senescence. Moreover, the morphological parameters, including the length of the shoots and roots, and the fresh and dry weights of the shoots and roots, showed that after 7 days of salt treatment, opr7opr8 had heavier and longer shoots than WT but slighter and shorter roots than WT. In addition, ion analysis showed that opr7opr8 accumulated less sodium but more potassium in the leaves than WT but more sodium and less potassium in the roots than WT, suggesting that JA deficiency causes higher salt stress to the roots but less stress to the leaves of the seedlings. Reactive oxygen species (ROS) analysis showed that opr7opr8 produced less H₂O₂ than WT in the leaves but more H₂O₂ in the roots under salt treatment, and correspondingly, ROS-scavenging enzymes superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) showed a similar variation, i.e., opr7opr8 has lower enzymatic activities in the shoots but higher activities in the roots than WT under salt treatment. For osmotic adjustment, opr7opr8 produced less proline in the shoots at 100 and 300 mM NaCl treatments but more in the roots than the WT roots under all salt treatments. In addition, the gene expression for abscisic acid (ABA) biosynthesis under salt stress was investigated. Results showed that the expression levels of four key enzymes of ABA biosynthesis, ZEP1, NCED5, AO1, and VP10, were significantly downregulated in the shoots as compared to WT under salt treatment. Putting all the data together, we concluded that JA-deficiency in maize seedlings reduced the salt-stress responses in the shoots but exaggerated the responses in the roots. In addition, endogenous JA acted as a positive regulator for the transportation of sodium ions from the roots to the shoots because the mutant opr7opr8 had a higher level of sodium in the roots but a significantly lower level in the shoots than WT. Furthermore, JA may act as a positive regulator for ABA biosynthesis in the leaves under salt stress.