Abiotic Stress Tolerance In Plants Research Articles

Research Progress in Soybean by Phytohormone Modulation and Metal Chelation over the Past Decade

Phytohormones have been acknowledged as an eco-friendly and alternative source for plant growth promotion and abiotic stress tolerance. Heavy metal stress has attained considerable attention worldwide because of its serious effects. Globally, it is a major cause of crop yield loss. Soybean is an important legume crop that continuously faces environmental stress, such as heavy metal stress. The application of plant growth regulators, such as phytohormones, enhances plant tolerance toward heavy metals. Phytohormones augment the interaction with plants. They improve plant productivity under stress due to the potential of phytostabilization. They are capable of enhancing metal stress tolerance by reducing oxidation stress. In the present review, an attempt has been made to summarize the role of phytohormones in metal chelation in a model plant, soybean. The results suggest that among the phytohormones, ABA, JA, SA ET, GA, and IAA are synergistic with metal chelation, whereas cytokinins are antagonistic. The application of phytohormones and corresponding microbes enhances the production of glutathione (GSH), which enhances metal tolerance by metal sequestration.

Systematic Analysis of Galactinol Synthase and Raffinose Synthase Gene Families in Potato and Their Expression Patterns in Development and Abiotic Stress Responses.

Raffinose family oligosaccharides (RFOs) are very important for plant growth, development, and abiotic stress tolerance. Galactinol synthase (GolS) and raffinose synthase (RFS) are critical enzymes involved in RFO biosynthesis. However, the whole-genome identification and stress responses of their coding genes in potato remain unexplored. In this study, four StGolS and nine StRFS genes were identified and classified into three and five subgroups, respectively. Remarkably, a total of two StGolS and four StRFS genes in potato were identified to form collinear pairs with those in both Arabidopsis and tomato, respectively. Subsequent analysis revealed that StGolS4 exhibited significantly high expression levels in transport-related tissues, PEG-6000, and ABA treatments, with remarkable upregulation under salt stress. Additionally, StRFS5 showed similar responses to StGolS4, but StRFS4 and StRFS8 gene expression increased significantly under salt treatment and decreased in PEG-6000 and ABA treatments. Overall, these results lay a foundation for further research on the functional characteristics and molecular mechanisms of these two gene families in response to ABA, salt, and drought stresses, and provide a theoretical foundation and new gene resources for the abiotic-stress-tolerant breeding of potato.

MdMPK3 and MdMPK6 fine-tune MdWRKY17-mediated transcriptional activation of the melatonin biosynthesis gene MdASMT7.

Melatonin (N-acetyl-5-methoxytryptamine) is a potent reactive oxygen species (ROS) scavenger that increases the biotic and abiotic stress tolerance in plants. The signaling and regulation pathways of melatonin in plants remain elusive. Here, we report that transgenic apple (Malus domestica) plants overexpressing the transcription factor gene, MdWRKY17, have higher melatonin contents and lower ROS levels than those of control, while the MdWRKY17 RNA interference (RNAi) lines show the reversed phenotype. The binding of MdWRKY17 to N-acetylserotonin O-methyltransferase7 (MdASMT7) directly promotes the MdASMT7 expression in the in vitro and in vivo. MdASMT7is a melatonin synthase that localizes to the plasma membrane. MdASMT7 overexpression rescued the lower melatonin contents of MdWRKY17-RNAi lines, confirming the role of MdWRKY17-MdASMT7 module in melatonin biosynthesis in apple. Furthermore, melatonin treatment activated the mitogen-activated kinases (MPKs) MdMPK3 and MdMPK6, which phosphorylate MdWRKY17 to promote transcriptional activation of MdASMT7. RNAi-mediated silencing of MdMPK3/6 decreases MdASMT7 expression in transgenic apple plants overexpressing MdWRKY17, which further confirms MdMPK3/6 fine-tunes MdWRKY17-mediated MdASMT7 transcription. This also forms a positive loop that melatonin activates MdMPK3/6 and thus accelerates the biosynthesis of itself via triggering MdMPK3/6-MdWRKY17-MdASMT7 pathway. This novel melatonin regulatory pathway not only have dissected the molecular mechanisms of melatonin biosynthesis but also provided an alternative approach for generating transgenic melatonin-rich apples which may benefits to human health.

Multi-Omics Pipeline and Omics-Integration Approach to Decipher Plant's Abiotic Stress Tolerance Responses.

The present day's ongoing global warming and climate change adversely affect plants through imposing environmental (abiotic) stresses and disease pressure. The major abiotic factors such as drought, heat, cold, salinity, etc., hamper a plant's innate growth and development, resulting in reduced yield and quality, with the possibility of undesired traits. In the 21st century, the advent of high-throughput sequencing tools, state-of-the-art biotechnological techniques and bioinformatic analyzing pipelines led to the easy characterization of plant traits for abiotic stress response and tolerance mechanisms by applying the 'omics' toolbox. Panomics pipeline including genomics, transcriptomics, proteomics, metabolomics, epigenomics, proteogenomics, interactomics, ionomics, phenomics, etc., have become very handy nowadays. This is important to produce climate-smart future crops with a proper understanding of the molecular mechanisms of abiotic stress responses by the plant's genes, transcripts, proteins, epigenome, cellular metabolic circuits and resultant phenotype. Instead of mono-omics, two or more (hence 'multi-omics') integrated-omics approaches can decipher the plant's abiotic stress tolerance response very well. Multi-omics-characterized plants can be used as potent genetic resources to incorporate into the future breeding program. For the practical utility of crop improvement, multi-omics approaches for particular abiotic stress tolerance can be combined with genome-assisted breeding (GAB) by being pyramided with improved crop yield, food quality and associated agronomic traits and can open a new era of omics-assisted breeding. Thus, multi-omics pipelines together are able to decipher molecular processes, biomarkers, targets for genetic engineering, regulatory networks and precision agriculture solutions for a crop's variable abiotic stress tolerance to ensure food security under changing environmental circumstances.

Alleviation of Shade Stress in Chinese Yew (Taxus chinensis) Seedlings with 5-Aminolevulinic Acid (ALA).

5-aminolevulinic acid (ALA) is a novel regulator that can promote plant growth, nitrogen uptake, and abiotic stress tolerance. Its underlying mechanisms, however, have not been fully investigated. In this study, the effects of ALA on morphology, photosynthesis, antioxidant systems, and secondary metabolites in two cultivars of 5-year-old Chinese yew (Taxus chinensis) seedlings, 'Taihang' and 'Fujian', were examined under shade stress (30% light for 30 days) using different doses of ALA (0, 30, and 60 mg/L). The findings from our study show that shade stress significantly reduced plant height, stem thickness, and crown width and increased malondialdehyde (MDA) levels. However, the application of 30 mg/L ALA effectively mitigated these effects, which further induced the activity of antioxidant enzymes under shade stress, resulting in the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) being increased by 10%, 16.4%, and 42.1%, and 19.8%, 20.1%, and 42% in 'Taihang' and 'Fujian', respectively. It also promoted their role in the absorption, conversion, and efficient use of light energy. Additionally, the use of 30 mg/L ALA caused a significant increase in the concentration of secondary metabolites, including polysaccharide (PC), carotenoid (CR), and flavonoids (FA), with increases of up to 46.1%, 13.4%, and 35.6% and 33.5%, 7.5%, and 57.5% in both yew cultivars, respectively, contributing to nutrient uptake. With ALA treatment, the yew seedlings showed higher chlorophyll (total chlorophyll, chlorophyll a and b) levels and photosynthesis rates than the seedlings that received the shade treatment alone. To conclude, the application of 30 mg/L ALA alleviated shade stress in yew seedlings by maintaining redox balance, protecting the photorespiratory system, and increasing organic metabolites, thus increasing the number of new branches and shoots and significantly promoting the growth of the seedlings. Spraying with ALA may be a sustainable strategy to improve the shade-resistant defense system of yew. As these findings increase our understanding of this shade stress response, they may have considerable implications for the domestication and cultivation of yew.

A cluster of mutagenesis revealed an osmotic regulatory role of the OsPIP1 genes in enhancing rice salt tolerance

Aquaporins play important regulatory roles in improving plant abiotic stress tolerance. To better understand whether the OsPIP1 genes collectively dominate the osmotic regulation in rice under salt stress, a cluster editing of the OsPIP1;1, OsPIP1;2 and OsPIP1;3 genes in rice was performed by CRISPR/Cas9 system. Sequencing showed that two mutants with Cas9-free, line 14 and line 18 were successfully edited. Briefly, line 14 deleted a single C base in both the OsPIP1;1 and OsPIP1;3 genes, and inserted a single T base in the OsPIP1;2 gene, respectively. While line 18 demonstrated an insertion of a single A base in the OsPIP1;1 gene and a single T base in both the OsPIP1;2 and OsPIP1;3 genes, respectively. Multiplex editing of the OsPIP1 genes significantly inhibited photosynthetic rate and accumulation of compatible metabolites, but increased MDA contents and osmotic potentials in the mutants, thus delaying rice growth under salt stress. Functional loss of the OsPIP1 genes obviously suppressed the expressions of the OsPIP1, OsSOS1, OsCIPK24 and OsCBL4 genes, and increased the influxes of Na+ and effluxes of K+/H+ in the roots, thus accumulating more Na+ in rice mutants under salt stress. This study suggests that the OsPIP1 genes are essential modulators collectively contributing to the enhancement of rice salt stress tolerance, and multiplex editing of the OsPIP1 genes provides insight into the osmotic regulation of the PIP genes.

Achieving abiotic stress tolerance in plants through antioxidative defense mechanisms.

Climate change has increased the overall impact of abiotic stress conditions such as drought, salinity, and extreme temperatures on plants. Abiotic stress adversely affects the growth, development, crop yield, and productivity of plants. When plants are subjected to various environmental stress conditions, the balance between the production of reactive oxygen species and its detoxification through antioxidant mechanisms is disturbed. The extent of disturbance depends on the severity, intensity, and duration of abiotic stress. The equilibrium between the production and elimination of reactive oxygen species is maintained due to both enzymatic and non-enzymatic antioxidative defense mechanisms. Non-enzymatic antioxidants include both lipid-soluble (α-tocopherol and β-carotene) and water-soluble (glutathione, ascorbate, etc.) antioxidants. Ascorbate peroxidase (APX), superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR) are major enzymatic antioxidants that are essential for ROS homeostasis. In this review, we intend to discuss various antioxidative defense approaches used to improve abiotic stress tolerance in plants and the mechanism of action of the genes or enzymes involved.

The basic helix-loop-helix transcription factor gene, OsbHLH38, plays a key role in controlling rice salt tolerance.

The plant hormone abscisic acid (ABA) is crucial for plant seed germination and abiotic stress tolerance. However, the association between ABA sensitivity and plant abiotic stress tolerance remains largely unknown. In this study, 436 rice accessions were assessed for their sensitivity to ABA during seed germination. The considerable diversity in ABA sensitivity among rice germplasm accessions was primarily reflected by the differentiation between the Xian (indica) and Geng (japonica) subspecies and between the upland-Geng and lowland-Geng ecotypes. The upland-Geng accessions were most sensitive to ABA. Genome-wide association analyses identified four major quantitative trait loci containing 21 candidate genes associated with ABA sensitivity of which a basic helix-loop-helix transcription factor gene, OsbHLH38, was the most important for ABA sensitivity. Comprehensive functional analyses using knockout and overexpression transgenic lines revealed that OsbHLH38 expression was responsive to multiple abiotic stresses. Overexpression of OsbHLH38 increased seedling salt tolerance, while knockout of OsbHLH38 increased sensitivity to salt stress. A salt-responsive transcription factor, OsDREB2A, interacted with OsbHLH38 and was directly regulated by OsbHLH38. Moreover, OsbHLH38 affected rice abiotic stress tolerance by mediating the expression of a large set of transporter genes of phytohormones, transcription factor genes, and many downstream genes with diverse functions, including photosynthesis, redox homeostasis, and abiotic stress responsiveness. These results demonstrated that OsbHLH38 is a key regulator in plant abiotic stress tolerance.

The emerging key role of reactive sulfur species in abiotic stress tolerance in plants.

In plants, sulfur plays a critical role in the formation of important biomolecules such as cysteine, methionine, and tripeptide glutathione. Thiol groups, composed of sulfur, are essential to numerous metabolic processes. The easy and reversible oxidation and reduction of thiol groups have drawn attention to the redox regulation of cellular metabolism. Reactive sulfur species (RSS), including hydrogen sulfide (H2 S), persulfides and polysulfides, are synthetized in all living organisms, mainly from cysteine, and have been recognized in the last two decades as very important molecules in redox regulation. RSS are considered potent signaling molecules, being involved in the regulation of virtually all aspects of cell function. With regard to stress, reactive species and the antioxidant machinery maintain a delicate balance that gets disturbed under stress conditions, wherein reactive species biosynthesis, transportation, scavenging, and overall metabolism become decisive for plant survival. While reactive oxygen and nitrogen species have been much discussed over recent years, research into reactive sulfur species (RSS) biosynthesis, signaling, and relation to abiotic stresses is still nascent. RSS evolved long before reactive oxygen species, and because both are metabolized by catalase, it has been suggested that "antioxidant" enzymes originally evolved to regulate RSS and may still do so today. In this review, we have tried to summarize the generation, signaling, and interaction of RSS in plant systems and to discuss in detail the roles under various abiotic stresses. This article is protected by copyright. All rights reserved.

ZmCIPK32 positively regulates germination of stressed seeds via gibberellin signal

Calcineurin B-like proteins (CBLs) as specific calcium sensors that interact with CBL-interacting protein kinases (CIPKs) play a key role in the regulation of plant development and abiotic stress tolerance. In this study, we isolated and characterized the CIPK32 gene from Zea mays. ZmCIPK32 showed that it comprised 440 amino acids and a conserved NAF motif responsible for the interaction with CBLs localized in the cytoplasm and cell membrane. The interaction of ZmCIPK32 with ZmCBL1 and ZmCBL9 demonstrated using yeast two-hybrid system and bimolecular fluorescence complementation assay required the presence of the NAF domain. Overexpression of ZmCIPK32 promoted early germination in transgenic Arabidopsis seeds relative to that observed in wild-type (WT) plants under mannitol treatment. In addition, ZmCIPK32-overexpressing plants were insensitive to treatments with exogenous abscisic acid and paclobutrazol (PBZ) at seed germination and early seedling stages. Expression levels of the key genes GA20ox and GA3ox involved in the synthesis of gibberellin (GA) were increased, whereas expression levels of genes involved in the conversion of active GA to inactive forms and GA signaling were reduced in ZmCIPK32-overexpressing plants relative to those in WT plants under mannitol and PBZ treatments. Furthermore, overexpression of ZmCIPK32 increased GA level but decreased abscisic acid level in transgenic lines compared to the respective levels in WT plants under PBZ or mannitol treatments. Our results suggest that ZmCIPK32 positively regulates seed germination under stressed conditions by modulating GA signals.

Cerium oxide- salicylic acid nanocomposite foliar use impacts physiological responses and essential oil composition of spearmint (Mentha spicata L.) under salt stress

Applying some compounds such as salicylic acid and cerium oxide can be a valuable method to improve abiotic stress tolerance in plants. To assay the effects of salicylic acid nanoparticles (SA-NPs), cerium oxide (CeO2NPs), and CeO2- SA nanocomposite on physiological, and biochemical properties and the percentage of essential oil of spearmint plant (Mentha spicata L.) under salinity stress, a factorial experiment was conducted based on a completely randomized design with 2 factors and 3 replications in greenhouse conditions. The first factor was three levels of salinity stress (0, 50, and 100 mM), and the second factor included T2 (100 µM SA-NPs), T3 (50 mg L − 1 CeO2NPs), T4 (25 mg L − 1 and 50 µM CeO2- SA nanocomposite) and T5 (50 mg L − 1 and 100 µM CeO2- SA nanocomposite). The activity of antioxidant enzymes such as superoxide dismutase, guaiacol peroxidase, ascorbate peroxidase, total soluble protein, malondialdehyde, hydrogen peroxide, proline, total ascorbate, the reduced and total AsA, DHA, AsA/DHA, elements (Na, K, Na /K, Zn, Cu, Mn, Fe) content, chlorophyll fluorescence (Fm, Fv, Fm/Fv, F0), percentage of essential oil, essential oil compounds and photosynthetic pigments content were evaluated. The results showed that with increasing salinity stress, the content of carbohydrates, protein, total antioxidants, carotenoids, chlorophyll a, chlorophyll b, and total chlorophyll decreased compared with the control. At the same time, cerium oxide-salicylic acid nanocomposite application improved protein, carbohydrate, phenolics, flavonoids, essential oil percentage, and total antioxidant capacity. However, proline, hydrogen peroxide, superoxide dismutase, guaiacol peroxidase, and ascorbate peroxidase increased significantly with enhancing salinity levels compared with the control. The application of cerium oxide-salicylic acid nanocomposite reduced the mentioned traits. The main essential oil constituents were pulegone, l-enthone, 1,8-cineole, a-terpinene, trans-caryophyllene, isopulegol, β-pinene, sabinene, and β-myrcene. Conclusively, the CeO2- SA nanocomposite positively reduced the undesirable impact of salinity stress.

A high-quality chromosome-level Eutrema salsugineum genome, an extremophile plant model

BackgroundEutrema salsugineum (2n = 14), a halophyte in the family Brassicaceae, is an attractive model to study abiotic stress tolerance in plants. Two versions of E. salsugineum genomes that previously reported were based on relatively short reads; thus, the repetitive regions were difficult to characterize.ResultsWe report the sequencing and assembly of the E. salsugineum (Shandong accession) genome using long-read sequencing and chromosome conformation capture data. We generated Oxford Nanopore long reads at high depth (> 60X) of genome coverage with additional short reads for error correction. The new assembly has a total size of 295.5 Mb with 52.8% repetitive sequences, and the karyotype of E. salsugineum is consistent with the ancestral translocation Proto-Calepineae Karyotype structure in both order and orientation. Compared with previous assemblies, this assembly has higher contiguity, especially in the centromere region. Based on this new assembly, we predicted 25,399 protein-coding genes and identified the positively selected genes associated with salt and drought stress responses.ConclusionThe new genome assembly will provide a valuable resource for future genomic studies and facilitate comparative genomic analysis with other plants.

Plant Metabolomics: An Overview of the Role of Primary and Secondary Metabolites against Different Environmental Stress Factors

Several environmental stresses, including biotic and abiotic factors, adversely affect the growth and development of crops, thereby lowering their yield. However, abiotic factors, e.g., drought, salinity, cold, heat, ultraviolet radiations (UVr), reactive oxygen species (ROS), trace metals (TM), and soil pH, are extremely destructive and decrease crop yield worldwide. It is expected that more than 50% of crop production losses are due to abiotic stresses. Moreover, these factors are responsible for physiological and biochemical changes in plants. The response of different plant species to such stresses is a complex phenomenon with individual features for several species. In addition, it has been shown that abiotic factors stimulate multi-gene responses by making modifications in the accumulation of the primary and secondary metabolites. Metabolomics is a promising way to interpret biotic and abiotic stress tolerance in plants. The study of metabolic profiling revealed different types of metabolites, e.g., amino acids, carbohydrates, phenols, polyamines, terpenes, etc, which are accumulated in plants. Among all, primary metabolites, such as amino acids, carbohydrates, lipids polyamines, and glycine betaine, are considered the major contributing factors that work as osmolytes and osmoprotectants for plants from various environmental stress factors. In contrast, plant-derived secondary metabolites, e.g., phenolics, terpenoids, and nitrogen-containing compounds (alkaloids), have no direct role in the growth and development of plants. Nevertheless, such metabolites could play a significant role as a defense by protecting plants from biotic factors such as herbivores, insects, and pathogens. In addition, they can enhance the resistance against abiotic factors. Therefore, metabolomics practices are becoming essential and influential in plants by identifying different phytochemicals that are part of the acclimation responses to various stimuli. Hence, an accurate metabolome analysis is important to understand the basics of stress physiology and biochemistry. This review provides insight into the current information related to the impact of biotic and abiotic factors on variations of various sets of metabolite levels and explores how primary and secondary metabolites help plants in response to these stresses.

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

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

Transcriptome and Proteome Analysis Identifies Salt Stress Response Genes in Bottle Gourd Rootstock-Grafted Watermelon Seedlings

Soil salinization poses a huge challenge to the development of agriculture and seriously decreases crop yield and quality. In recent years, grafting has become one of the key agronomic techniques used to enhance plant abiotic stress tolerance. In this study, we found that watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] grafted onto bottle gourd (Lagenaria siceraria Standl.) significantly enhanced salt tolerance. Transcriptome analysis revealed that a total of 8462 differentially expressed genes (DEGs) were identified, and the number of up- and down-regulated genes were 3207 and 5255, respectively. The DEGs in the bottle gourd rootstock-grafted plants were mainly involved in carbon metabolism, photosynthesis, and plant hormone signal transduction. Furthermore, proteome analysis identified 28 differently expressed proteins (DEPs) in bottle gourd rootstock-grafted plants under salt stress. These DEPs were closely associated with amino acid and protein synthesis, photosynthesis, mitochondrial metabolism and carbon metabolism, and stress defense. Combined transcriptome and proteome analyses showed that salt stress-responded genes in bottle gourd rootstock-grafted watermelon seedlings were mainly involved in plant hormone signal transduction, photosynthesis, and amino acid synthesis pathways.

Elucidating molecular characterization of chlorpyrifos and profenofos degrading distinct bacterial strains for enhancing seed germination potential of Gossypium arboreum L.

Chlorpyrifos (CP) and profenofos (PF) are organophosphate pesticides (OPs) widely used in agriculture and are noxious to both fauna and flora. The presented work was designed to attenuate the toxicity of both pesticides in the growth parameters of a cotton crop by applying plant growth-promoting rhizobacteria (PGPR), namely Pseudomonas aeruginosa PM36 and Bacillus sp. PM37. The multifarious biological activities of both strains include plant growth-promoting traits, including phosphate solubilization; indole-3-acetic acid (IAA), siderophore, and HCN production; nitrogen fixation; and enzymatic activity such as cellulase, protease, amylase, and catalase. Furthermore, the molecular profiling of multi-stress-responsive genes, including acdS, ituC, czcD, nifH, and sfp, also confirmed the plant growth regulation and abiotic stress tolerance potential of PM36 and PM37. Both strains (PM36 and PM37) revealed 92% and 89% of CP degradation at 50ppm and 87% and 81% at 150ppm within 7days. Simultaneously 94% and 98% PF degradation was observed at 50ppm and 90% and 92% at 150ppm within 7days at 35°C and pH 7. Biodegradation was analyzed using HPLC and FTIR. The strains exhibited first-order reaction kinetics, indicating their reliance on CP and PF as energy and carbon sources. The presence of opd, mpd, and opdA genes in both strains also supported the CP and PF degradation potential of both strains. Inoculation of strains under normal and OP stress conditions resulted in a significant increase in seed germination, plant biomass, and chlorophyll contents of the cotton seedling. Our findings indicate that the strains PM36 and PM37 have abilities as biodegraders and plant growth promoters, with potential applications in crop sciences and bioremediation studies. These strains could serve as an environmentally friendly, sustainable, and socially acceptable solution to manage OP-contaminated sites.

Exogenously applied melatonin enhanced the tolerance of Brassica napus against cobalt toxicity by modulating antioxidant defense, osmotic adjustment, and expression of stress response genes

The excessive accumulation of cobalt (Co) in plant tissues severely impairs plant growth that ultimately reduces the yield. However, melatonin (MT) has been known to mediate the abiotic stress tolerance in plants. The present study aimed at investigating the protective mechanisms of exogenously applied MT (0, 50 and 100 μM) under Co (0, 100, 200 and 300 μM) stress by focusing on morpho-physiological, biochemical and cellular characterizations of Brassica napus plants. Cobalt (300 μM) alone treatment drastically inhibited the stomatal conductance, plant height (45%), leaf area (30%), free amino acid (139%), relative electrolyte leakage (109%), and total soluble sugars (71%), compared with the control. However, the exogenous supply of MT notably minimized the oxidative damage, lipid peroxidation and maintained the membrane integrity under Co-toxicity by restricting the overproduction of ROS (H2O2 and O2•), and MDA in leaves and roots. Melatonin significantly enhanced the activities of ROS-scavenging antioxidant enzymes, secondary metabolism-related phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), stress-responsive genes (heat shock protein as HSP-90, methyl transferase as MT) and regulated the Co-transporters, especially in roots. These findings indicated that an exogenous supply of MT improve the plant morphology, photosynthetic apparatus, osmotic adjustments, and antioxidant defense systems by enhancing the Co-detoxification in B. napus plants.

Exogenous application of Bradyrhizobium japonicum AC20 enhances soybean tolerance to atrazine via regulating rhizosphere soil microbial community and amino acid, carbohydrate metabolism related genes expression

Atrazine is used to control broad-leaved weeds in farmland and has negative impacts on soybean growth. Legume-rhizobium symbiosis plays an important role in regulating abiotic stress tolerance of plants, however, the mechanisms of rhizobia regulate the tolerance of soybean to atrazine based on the biochemical responses of the plant-soil system are limited. In this experiment, Glycine max (L.) Merr. Dongnong 252, planted in 20 mg kg−1 of atrazine-contaminated soil, was inoculated with Bradyrhizobium japonicum AC20, and the plant growth, rhizosphere soil microbial diversity and the expression of the genes related to soybean carbon and nitrogen metabolism were assessed. The results indicated that strain AC20 inoculation alleviated atrazine-induced growth inhibition via increasing the contents of leghemoglobin and total nitrogen in soybean seedlings. The psbA gene expression level of the soybean seedlings that inoculated strain AC20 was 1.4 times than that of no rhizobium inoculating treatments. Moreover, the inoculated AC20 increased the abundance of Acidobacteria and Actinobacteria in soybean rhizosphere. Transcriptome analysis demonstrated that strain AC20 regulated the genes expression of amino acid metabolism and carbohydrate metabolism of soybean seedlings. Correlation analysis between 16S rRNA and transcriptome showed that strain AC20 reduced Planctomycetes abundance so as to down-regulated the expression of genes Glyma. 13G087800, Glyma. 12G005100 and Glyma.12G098900 involved in starch synthesis pathway of soybean leaves. These results provide available information for the rhizobia application to enhance the atrazine tolerate in soybean seedlings.

Polyamines and nitric oxide crosstalk in plant development and abiotic stress tolerance.

Polyamines (PAs) and nitric oxide (NO) are crucial signalling molecules that exhibit a promising role in improving stress tolerance in plants, maintaining their growth and development. They act as protecting agents for plants through activation of stress adaptation strategies such as membrane stabilisation, acid neutralisation and suppression of ROS generation. NO interacts with PAs during several developmental processes and stress responses. External supplementation of PAs to plants is also reported to cause an increase in NO content. However, it is unclear whether PAs promote synthesis of NO by either as substrates, cofactors, or signals. Impact of NO on synthesis of PAs has been also reported in some studies, yet the exact governing mechanisms of the interrelation between NO and PAs is currently obscure. Understanding the crosstalk between PAs and NO during growth and stress condition in plants can aid in providing better tolerance to plants against stressful environment.

Overexpression of an autophagy-related gene DiATG3 from Davidia involucrata improves plant thermotolerance by enhancing the accumulation of polyamines and regulating genes in calcium and MAPK signaling pathways

Autophagy, a conserved eukaryotic mechanism for degrading intracellular constituents, plays prominent roles in plant abiotic stress tolerance. This study aimed to isolate an autophagy-related gene DiATG3 from a cool-adapted endangered plant species, dove tree (Davidia involucrata Baill.), and to investigate the physiological functions and regulatory mechanisms of DiATG3 for improving heat tolerance. DiATG3 was found to mainly localize to cytoplasm and possess the N-terminal domain, the catalytic domain with the HPC motif, and the C-terminal domain with the FLKF motif. Elevated transcript level of DiATG3 was detected in D. involucrata treated with heat stress. The constitutive overexpression of DiATG3 in Arabidopsis led to elevated levels of autophagy and conferred tolerance under heat stress. Furthermore, this thermotolerant phenotype was associated with improved photosynthetic capacity, higher antioxidant enzyme activities, and increased accumulation of polyamines. Transcriptome analysis suggest that activated calcium signaling and mitogen-activated protein kinase (MAPK) cascade may act as a central hub necessary for DiATG3-mediated heat tolerance. In addition, DiATG3 overexpression resulted in up-regulated expression of stress-related genes including heat shock factor A3 (AtHSFA3), dehydration-responsive element-binding protein 2C (AtDREB2C), AtWRKY26, and AtWRKY33 after heat treatment. Our study could yield insights into the engagement of plant autophagy during abiotic stress responses and contribute to breeding and engineering thermotolerant endangered plant species.