Coping with abiotic stress: proteome changes for crop improvement

Impact of homologous overexpression of PR10a gene on improving salt stress tolerance in transgenic Solanum tuberosum

Abiotic stresses severely affected crop productivity and considered to be a major yield limiting factor for crop plant. The tolerance to these stresses is a very complex phenomenon involving a wide array of molecular, biochemical and physiological changes in plant cells. Therefore, it is challenging to understand the molecular basis of abiotic stress tolerance to manipulate it for improving abiotic stress tolerance of major crops. Biotechnological approaches and genetic engineering including homologous gene overexpression can be implemented to understand gene functions under well-defined conditions. The Pathogenesis-related proteins (PR10) such as PR10a play multiple roles in biotic and abiotic stress tolerance and, hence, plant development. A PR10a gene from potato cv. Deseree was introduced into three cultivars of potato (Solanum tuberosum L.) by Agrobacterium tumefaciens-mediated genetic transformation. Transgenic plants were selected on a medium containing 1.0 mg/l phosphinothricin (PPT) and confirmed by polymerase chain reaction (PCR), herbicide (BASTA®) leaf paint assay, and Real-Time- quantitative PCR analyses (qPCR). All of the selected transformants showed completely tolerance to the application of PPT application. Experiments designed for testing salt tolerance revealed that there was enhanced salt tolerance of the transgenic lines in vitro in terms of morphological (plant FW, plant DW and plant height) and antioxidant activates as compared to the non-transgenic control plants. qRT-PCR showed that the expression of PR10a gene in the transgenic potato is higher than that in non-transgenic control under salt stress. The relative PR10a gene-expression patterns in the transgenic plants shed lights into the molecular response of homologues overexpressed PR10a potato to salt-stress conditions. The obtained results provide insights on the fact that PR10a plays a major role regarding salt stress tolerance in potato plants.

Multiomics analyses reveal the central role of the nucleolus and its machinery during heat stress acclimation in Pinus radiata

Global warming is causing rapid changes in mean annual temperature and more severe drought periods. These are major contributors of forest dieback, which is becoming more frequent and widespread. In this work, we investigated how the transcriptome of Pinus radiata changed during initial heat stress response and acclimation. To this end, we generated a high-density dataset employing Illumina technology. This approach allowed us to reconstruct a needle transcriptome, defining 12 164 and 13 590 transcripts as down- and up-regulated, respectively, during a time course stress acclimation experiment. Additionally, the combination of transcriptome data with other available omics layers allowed us to determine the complex inter-related processes involved in the heat stress response from the molecular to the physiological level. Nucleolus and nucleoid activities seem to be a central core in the acclimating process, producing specific RNA isoforms and other essential elements for anterograde-retrograde stress signaling such as NAC proteins (Pra_vml_051671_1 and Pra_vml_055001_5) or helicase RVB. These mechanisms are connected by elements already known in heat stress response (redox, heat-shock proteins, or abscisic acid-related) and with others whose involvement is not so well defined such as shikimate-related, brassinosteriods, or proline proteases together with their potential regulatory elements. This work provides a first in-depth overview about molecular mechanisms underlying the heat stress response and acclimation in P. radiata.

Multi-omics assisted breeding for biotic stress resistance in soybean

Biotic stress is a critical factor limiting soybean growth and development. Soybean responses to biotic stresses such as insects, nematodes, fungal, bacterial, and viral pathogens are governed by complex regulatory and defense mechanisms. Next-generation sequencing has availed research techniques and strategies in genomics and post-genomics. This review summarizes the available information on marker resources, quantitative trait loci, and marker-trait associations involved in regulating biotic stress responses in soybean. We discuss the differential expression of related genes and proteins reported in different transcriptomics and proteomics studies and the role of signaling pathways and metabolites reported in metabolomic studies. Recent advances in omics technologies offer opportunities to reshape and improve biotic stress resistance in soybean by altering gene regulation and/or other regulatory networks. We suggest using 'integrated omics' to precisely understand how soybean responds to different biotic stresses. We also discuss the potential challenges of integrating multi-omics for the functional analysis of genes and their regulatory networks and the development of biotic stress-resistant cultivars. This review will help direct soybean breeding programs to develop resistance against different biotic stresses.

Proteomic Analysis Comparison on the Ecological Adaptability of Quinclorac-Resistant Echinochloa crus-galli

Barnyardgrass (Echinochloa crus-galli L.) is the most serious weed threatening rice production, and its effects are aggravated by resistance to the quinclorac herbicide in the Chinese rice fields. This study conducted a comparative proteomic characterization of the quinclorac-treated and non-treated resistant and susceptible E. crus-galli using isobaric tags for relative and absolute quantification (iTRAQ). The results indicated that the quinclorac-resistant E. crus-galli had weaker photosynthesis and a weaker capacity to mitigate abiotic stress, which suggested its lower environmental adaptability. Quinclorac treatment significantly increased the number and expression of the photosynthesis-related proteins in the resistant E. crus-galli and elevated its photosynthetic parameters, indicating a higher photosynthetic rate compared to those of the susceptible E. crus-galli. The improved adaptability of the resistant E. crus-galli to quinclorac stress could be attributed to the observed up-regulated expression of eight herbicide resistance-related proteins and the down-regulation of two proteins associated with abscisic acid biosynthesis. In addition, high photosynthetic parameters and low glutathione thiotransferase (GST) activity were observed in the quinclorac-resistant E. crus-galli compared with the susceptible biotype, which was consistent with the proteomic sequencing results. Overall, this study demonstrated that the resistant E. crus-galli enhanced its adaptability to quinclorac by improving the photosynthetic efficiency and GST activity.

Adaptation of protein phosphatases in Oryza sativa and Cucumis sativus to microcystins

Microcystins (MCs) in irrigation water could inhibit crop growth and yield. Protein phosphatases (PPs) play an important role in regulating physiological mechanisms in plants to adapt abiotic stresses. To clarify the adaptation mechanism in plants to MCs stress, we compared PPs in rice and cucumber leaves by analyzing PPs total activity, protein phosphatase-2A (PP2A) activity and expression, as well as related growth and gas exchange parameters. After 7-day exposure of MCs (5 ~ 100 µg/L) and 7-day recovery without MCs, rice showed higher tolerance to MCs by analyzing dry weight and gas exchange parameters. Both crops may regulate PPs activity to adapt MCs stress by increasing the expression of genes encoding PPs. Among them, PP2A activity in two crops showed more sensitivity to MCs than total PPs activity. In addition, the higher expressions of PP2A catalytic and regulatory subunits and lower decrease PP2A activity were observed in rice leaves compared to cucumber. All results suggest that the expression levels of PP2A subunits could play a role in maintaining the activity of PP2A to regulating plant tolerance to MCs stress.

Responses of the tree peony (Paeonia suffruticosa, Paeoniaceae) cultivar 'Yu Hong' to heat stress revealed by iTRAQ-based quantitative proteomics

Horticulture productivity has been increasingly restricted by heat stress from growing global warming, making it far below the optimum production capacity. As a popular ornamental cultivar of tree peony, Paeonia suffruticosa 'Yu Hong' has also been suffering from heat stress not suitable for its optimal growth. To better understand the response mechanisms against heat stress of tree peony, investigations of phenotypic changes, physiological responses, and quantitative proteomics were conducted. Phenotypic and physiological changes indicated that 24 h of exposure to heat stress (40 °C) was the critical duration of heat stress in tree peony. The proteomic analyses revealed a total of 100 heat-responsive proteins (HRPs). According to bioinformatic analysis of HRPs, the heat tolerance of tree peony might be related to signal transduction, synthesis/degradation, heat kinetic proteins, antioxidants, photosynthesis, energy conversion, and metabolism. Our research will provide some new insights into the molecular mechanism under the response against the heat stress of tree peony, which will benefit the future breeding of heat-resistant ornamental plants.

Cotton proteomics: Dissecting the stress response mechanisms in cotton

The natural environment of plants comprises a complex set of biotic and abiotic stresses, and plant responses to these stresses are complex as well. Plant proteomics approaches have significantly revealed dynamic changes in plant proteome responses to stress and developmental processes. Thus, we reviewed the recent advances in cotton proteomics research under changing environmental conditions, considering the progress and challenging factors. Finally, we highlight how single-cell proteomics is revolutionizing plant research at the proteomics level. We envision that future cotton proteomics research at the single-cell level will provide a more complete understanding of cotton's response to stresses.

Advances in mass spectrometry-based phosphoproteomics for elucidating abscisic acid signaling and plant responses to abiotic stress

Abiotic stresses have significant impacts on crop yield and quality. Even though significant efforts during the past decade have been devoted to uncovering the core signaling pathways associated with the phytohormone abscisic acid (ABA) and abiotic stress in plants, abiotic stress signaling mechanisms in most crops remain largely unclear. The core components of the ABA signaling pathway, including early events in the osmotic stress-induced phosphorylation network, have recently been elucidated in Arabidopsis with the aid of phosphoproteomics technologies. We now know that SNF1-related kinases 2 (SnRK2s) are not only inhibited by the clade A type 2C protein phosphatases (PP2Cs) through dephosphorylation, but also phosphorylated and activated by upstream mitogen-activated protein kinase kinase kinases (MAP3Ks). Through describing the course of studies to elucidate abiotic stress and ABA signaling, we will discuss how we can take advantage of the latest innovations in mass-spectrometry-based phosphoproteomics and structural proteomics to boost our investigation of plant regulation and responses to ABA and abiotic stress.

Understanding the salinity stress on plant and developing sustainable management strategies mediated salt-tolerant plant growth-promoting rhizobacteria and CRISPR/Cas9

Soil salinity is a worldwide concern that decreases plant growth performance in agricultural fields and contributes to food scarcity. Salt stressors have adverse impacts on the plant's ionic, osmotic, and oxidative balance, as well as numerous physiological functions. Plants have a variety of coping strategies to deal with salt stress, including osmosensing, osmoregulation, ion-homeostasis, increased antioxidant synthesis, and so on. Not only does salt stress cause oxidative stress but also many types of stress do as well, thus plants have an effective antioxidant system to battle the negative effects of excessive reactive oxygen species produced as a result of stress. Rising salinity in the agricultural field affects crop productivity and plant development considerably; nevertheless, plants have a well-known copying mechanism that shields them from salt stress by facilitated production of secondary metabolites, antioxidants, ionhomeostasis, ABAbiosynthesis, and so on. To address this problem, various environment-friendly solutions such as salt-tolerant plant growth-promoting rhizobacteria, eco-friendly additives, and foliar applications of osmoprotectants/antioxidants are urgently needed. CRISPR/Cas9, a new genetic scissor, has recently been discovered to be an efficient approach for reducing salt stress in plants growing in saline soil. Understanding the processes underlying these physiological and biochemical responses to salt stress might lead to more effective crop yield control measures in the future. In order to address this information, the current review discusses recent advances in plant stress mechanisms against salinity stress-mediated antioxidant systems, as well as the development of appropriate long-term strategies for plant growth mediated by CRISPR/Cas9 techniques under salinity stress.

Physiological and Metabolic Responses of Gac Leaf (Momordica cochinchinensis (Lour.) Spreng.) to Salinity Stress

Gac is a carotenoid-rich, healthful tropical fruit; however, its productivity is limited by soil salinity, a growing environmental stress. This study aimed to evaluate the effects of salinity stress on key physiological traits and metabolites in 30-day-old gac seedling leaves, treated with 0, 25-, 50-, 100-, and 150-mM sodium chloride (NaCl) for four weeks to identify potential alarm, acclimatory, and exhaustion responses. Electrolyte leakage increased with increasing NaCl concentrations (p < 0.05) indicating loss of membrane permeability and conditions that lead to reactive oxygen species production. At 25 and 50 mM NaCl, superoxide dismutase (SOD) activity, starch content, and total soluble sugar increased. Chlorophyll a, and total chlorophyll increased at 25 mM NaCl but decreased at higher NaCl concentrations indicating salinity-induced thylakoid membrane degradation and chlorophyllase activity. Catalase (CAT) activity decreased (p < 0.05) at all NaCl treatments, while ascorbate peroxidase (APX) and guaiacol peroxidase (GPX) activities were highest at 150 mM NaCl. GC-MS-metabolite profiling showed that 150 mM NaCl induced the largest changes in metabolites and was thus distinct. Thirteen pathways and 7.73% of metabolites differed between the control and all the salt-treated seedlings. Salinity decreased TCA cycle intermediates, and there were less sugars for growth but more for osmoprotection, with the latter augmented by increased amino acids. Although 150 mM NaCl level decreased SOD activity, the APX and GPX enzymes were still active, and some carbohydrates and metabolites also accumulated to promote salinity resistance via multiple mechanisms.

Potential application of TurboID-based proximity labeling in studying the protein interaction network in plant response to abiotic stress

Abiotic stresses are major environmental conditions that reduce plant growth, productivity and quality. Protein-protein interaction (PPI) approaches can be used to screen stress-responsive proteins and reveal the mechanisms of protein response to various abiotic stresses. Biotin-based proximity labeling (PL) is a recently developed technique to label proximal proteins of a target protein. TurboID, a biotin ligase produced by directed evolution, has the advantages of non-toxicity, time-saving and high catalytic efficiency compared to other classic protein-labeling enzymes. TurboID-based PL has been successfully applied in animal, microorganism and plant systems, particularly to screen transient or weak protein interactions, and detect spatially or temporally restricted local proteomes in living cells. This review concludes classic PPI approaches in plant response to abiotic stresses and their limitations for identifying complex network of regulatory proteins of plant abiotic stresses, and introduces the working mechanism of TurboID-based PL, as well as its feasibility and advantages in plant abiotic stress research. We hope the information summarized in this article can serve as technical references for further understanding the regulation of plant adaptation to abiotic stress at the protein level.

GWAS and RNA-seq analysis uncover candidate genes associated with alkaline stress tolerance in maize (Zea mays L.) seedlings

Soil salt-alkalization is a common yet critical environmental stress factor for plant growth and development. Discovering and exploiting genes associated with alkaline tolerance in maize (Zea mays L.) is helpful for improving alkaline resistance. Here, an association panel consisting of 200 maize lines was used to identify the genetic loci responsible for alkaline tolerance-related traits in maize seedlings. A total of nine single-nucleotide polymorphisms (SNPs) and their associated candidate genes were found to be significantly associated with alkaline tolerance using a genome-wide association study (GWAS). An additional 200 genes were identified when the screen was extended to include a linkage disequilibrium (LD) decay distance of r2 ≥ 0.2 from the SNPs. RNA-sequencing (RNA-seq) analysis was then conducted to confirm the linkage between the candidate genes and alkali tolerance. From these data, a total of five differentially expressed genes (DEGs; |log2FC| ≥ 0.585, p < 0.05) were verified as the hub genes involved in alkaline tolerance. Subsequently, two candidate genes, Zm00001d038250 and Zm00001d001960, were verified to affect the alkaline tolerance of maize seedlings by qRT-PCR analysis. These genes were putatively involved protein binding and "flavonoid biosynthesis process," respectively, based on Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) enrichment analyses. Gene promoter region contains elements related to stress and metabolism. The results of this study will help further elucidate the mechanisms of alkaline tolerance in maize, which will provide the groundwork for future breeding projects.

Transcriptomic Profile Analysis of Populus talassica × Populus euphratica Response and Tolerance under Salt Stress Conditions

A new Populus variety with a strong salt tolerance was obtained from cross breeding P. talassica as the female parent and P. euphratica as the male parent. In order to elucidate the molecular mechanism and find out the major differentially expressed genes of salt tolerance of P. talassica × P. euphratica, after being subjected to salt stress, at 0, 200, and 400 mmol/L NaCl, the root, stem, and leaf transcriptomes (denoted as R0, S0, and L0; R200, S200, and L200; and R400, S400, and L400, respectively) of P. talassica × P. euphratica were sequenced. In total, 41,617 differentially expressed genes (DEGs) were identified in all the comparison groups with 21,603 differentially upregulated genes and 20,014 differentially downregulated genes. Gene Ontology analysis showed that DEGs were significantly enriched in biological processes that may be involved in salt stress, such as ‘cell communication’, ‘ion transport’, ‘signaling’, and signal ‘transmission’. Kyoto Encyclopedia of Genes and Genomes analysis showed that DEGs were mainly enriched in pathways of ‘plant–pathogen interaction’, ‘carbon metabolism’, and ‘plant hormone signal transmission’. The pathways and related gene information formed a basis for future research on the mechanisms of salt stress, the development of molecular markers, and the cloning of key genes in P. talassica × P. euphratica.

Influence of Salinity Stress on Color Parameters, Leaf Pigmentation, Polyphenol and Flavonoid Contents, and Antioxidant Activity of Amaranthus lividus Leafy Vegetables

This is the first attempt to evaluate the impact of four salinity levels on the color parameters, pigments, polyphenols, flavonoids, and antioxidant capacities of four promising A. lividus genotypes. The color parameters, such as the yellowness/blueness (b*) and the chroma (C*); the antioxidant components, such as the polyphenols and flavonoids; and the antioxidant capacities of the leaves were remarkably increased by 39, 1, 5, 10 and 43%, respectively, at 50 mM of NaCl, and by 55, 5, 60, 34, 58 and 82%, respectively, at 100 mM NaCl concentrations. The green tower and SA6 genotypes were identified as tolerant varieties. The total phenolic content (TPC) and the total flavonoid content (TFC) played vital roles in scavenging reactive oxygen species (ROS), and they would be beneficial for the human diet and would serve as good antioxidants for the prevention of aging, and they are also essential to human health. A correlation study revealed the strong antioxidant capacities of the pigments and antioxidant components that were studied. It was revealed that A. lividus could tolerate a certain level of salinity stress without compromising the antioxidant quality of the final product. Taken together, our results suggest that A. lividus could be a promising alternative crop for farmers, especially in saline-prone areas in the tropical and subtropical regions.

Integrated transcriptomic and proteomic analysis of Tritipyrum provides insights into the molecular basis of salt tolerance

Background

Soil salinity is a major environmental stress that restricts crop growth and yield.

Methods

Here, crucial proteins and biological pathways were investigated under salt-stress and recovery conditions in Tritipyrum ‘Y1805’ using the data-independent acquisition proteomics techniques to explore its salt-tolerance mechanism.

Results

In total, 44 and 102 differentially expressed proteins (DEPs) were identified in ‘Y1805’ under salt-stress and recovery conditions, respectively. A proteome-transcriptome-associated analysis revealed that the expression patterns of 13 and 25 DEPs were the same under salt-stress and recovery conditions, respectively. ‘Response to stimulus’, ‘antioxidant activity’, ‘carbohydrate metabolism’, ‘amino acid metabolism’, ‘signal transduction’, ‘transport and catabolism’ and ‘biosynthesis of other secondary metabolites’ were present under both conditions in ‘Y1805’. In addition, ‘energy metabolism’ and ‘lipid metabolism’ were recovery-specific pathways, while ‘antioxidant activity’, and ‘molecular function regulator’ under salt-stress conditions, and ‘virion’ and ‘virion part’ during recovery, were ‘Y1805’-specific compared with the salt-sensitive wheat ‘Chinese Spring’. ‘Y1805’ contained eight specific DEPs related to salt-stress responses. The strong salt tolerance of ‘Y1805’ could be attributed to the strengthened cell walls, reactive oxygen species scavenging, osmoregulation, phytohormone regulation, transient growth arrest, enhanced respiration, transcriptional regulation and error information processing. These data will facilitate an understanding of the molecular mechanisms of salt tolerance and aid in the breeding of salt-tolerant wheat.

Ascorbate-Glutathione Oxidant Scavengers, Metabolome Analysis and Adaptation Mechanisms of Ion Exclusion in Sorghum under Salt Stress

Salt stress is one of the major significant restrictions that hamper plant development and agriculture ecosystems worldwide. Novel climate-adapted cultivars and stress tolerance-enhancing molecules are increasingly appreciated to mitigate the detrimental impacts of adverse stressful conditions. Sorghum is a valuable source of food and a potential model for exploring and understanding salt stress dynamics in cereals and for gaining a better understanding of their physiological pathways. Herein, we evaluate the antioxidant scavengers, photosynthetic regulation, and molecular mechanism of ion exclusion transporters in sorghum genotypes under saline conditions. A pot experiment was conducted in two sorghum genotypes viz. SSG 59-3 and PC-5 in a climate-controlled greenhouse under different salt concentrations (60, 80, 100, and 120 mM NaCl). Salinity drastically affected the photosynthetic machinery by reducing the accumulation of chlorophyll pigments and carotenoids. SSG 59-3 alleviated the adverse effects of salinity by suppressing oxidative stress (H2O2) and stimulating enzymatic and non-enzymatic antioxidant activities (SOD, APX, CAT, POD, GR, GST, DHAR, MDHAR, GSH, ASC, proline, GB), as well as protecting cell membrane integrity (MDA, electrolyte leakage). Salinity also influenced Na+ ion efflux and maintained a lower cytosolic Na+/K+ ratio via the concomitant upregulation of SbSOS1, SbSOS2, and SbNHX-2 and SbV-Ppase-II ion transporter genes in sorghum genotypes. Overall, these results suggest that Na+ ions were retained and detoxified, and less stress impact was observed in mature and younger leaves. Based on the above, we deciphered that SSG 59-3 performed better by retaining higher plant water status, photosynthetic assimilates and antioxidant potential, and the upregulation of ion transporter genes and may be utilized in the development of resistant sorghum lines in saline regions.

Characterization of Selected Plant Growth-Promoting Rhizobacteria and Their Non-Host Growth Promotion Effects

Plant growth-promoting rhizobacteria (PGPR) are a functionally diverse group of microbes having immense potential as biostimulants and biopesticides. We isolated four PGPR (designated n, L, K, and Y) that confer growth-promoting effects on Arabidopsis thaliana. The present study describes the detailed polyphasic characterization of these PGPR. Classical methods of bacterial identification and biochemical test kits (API20E, API20NE, API ZYM, and API 50CH) revealed their metabolic versatility. All rhizobacterial isolates were positive for 1-aminocyclopropane-1-carboxylate (ACC) deaminase (ACCD) and indole acetic acid production and phosphorous solubilization. PCR analysis confirmed the presence of the nifH gene in strains n, L, and Y, showing their N2-fixation potential. In vitro dual culture methods and bacterial infestation in planta demonstrated that strains n and L exerted antagonistic effects on Pseudomonas syringae pv. tomato DC3000 and Botrytis cinerea 191 and provided protection to Arabidopsis plants against both phytopathogens. Short- or long-term bacterial treatment revealed significant changes in transcript levels of genes annotated to stress response and hormone metabolism in A. thaliana. In particular, the expression of stress-responsive genes in A. thaliana showed an upregulation under salinity stress. MAP kinase 6 (MPK6) was involved in the growth promotion induced by the four bacterial strains. Furthermore, these strains caused a significant increase in root dry weight of maize seedlings under gnotobiotic conditions. We conclude that the four rhizobacteria are good candidates as biofertilizers for enhancing growth of maize, among which strains n and L showed marked plant growth-promoting attributes and the potential to be exploited as functional biostimulants and biopesticides for sustainable agriculture. IMPORTANCE There are pressing needs to reduce the use of agrochemicals, and PGPR are receiving increasing interest in plant growth promotion and disease protection. This study follows up our previous report that the four newly isolated rhizobacteria promote the growth of Arabidopsis thaliana. We test the hypothesis that they have multiple PGP traits and that they can be used as biofertilizers and biopesticides. In vitro assays indicated that these four strains have various PGP properties related to nutrient availability, stress resistance, and/or pest organism antagonism. They significantly influenced the transcript levels of genes involved in stress response and hormone metabolism in A. thaliana. MPK6 is indispensable to the growth stimulation effects. Strains n and L protected A. thaliana seedlings against phytopathogens. Three strains significantly increased maize growth in vitro. In summary, introducing these four strains onto plant roots provides a benefit to the plants. This is the first study regarding the potential mechanism(s) applied by Mucilaginibacter sp. as biostimulants.

Stability of thylakoid protein complexes and preserving photosynthetic efficiency are crucial for the successful recovery of the halophyte Cakile maritima from high salinity

Plants native to extreme habitats often face changes in environmental conditions such as salinity level and water availability. In response, plants have evolved efficient mechanisms allowing them to survive or recover. In the present work, effects of high salinity and salt-stress release were studied on the halophyte Cakile maritima. Four week-old plants were either cultivated at 0 mM NaCl or 200 mM NaCl. After one month of treatment, plants were further irrigated at either 0 mM NaCl, 200 mM NaCl, or rewatered to 0 mM NaCl (stress release). Upon salt stress, C. maritima plants exhibited reduced biomass production and shoot hydration which were associated with a decrease in the amount of chlorophyll a and b. However, under the same stressful conditions a significant increase of anthocyanin and malonyldialdehyde concentrations was noticed. Salt-stressed plants were able to maintain stable protein complexes of thylakoid membranes. Measurement of chlorophyll fluorescence and P700 redox state showed that PSI was more susceptible for damage by salinity than PSII. PSII machinery was significantly enhanced under saline conditions. All measured parameters were partially restored under salt-stress release conditions. Photoinhibition of PSI was also reversible and C. maritima was able to successfully re-establish PSI machinery indicating the high contribution of chloroplasts in salt tolerance mechanisms of C. maritima. Overall, to overcome high salinity stress, C. maritima sets a cascade of physio-biochemical and molecular pathways. Chloroplasts seem to act as metabolic centers as part of this adaptive process enabling growth restoration in this halophyte following salt stress release.

Stress response of lettuce (Lactuca sativa) to environmental contamination with selected pharmaceuticals: A proteomic study

Pharmaceutical compounds have been found in rivers and treated wastewaters. They often contaminate irrigation waters and consequently accumulate in edible vegetables, causing changes in plants metabolism. The main objective of this work is to understand how lettuce plants cope with the contamination from three selected pharmaceuticals using a label free proteomic analysis. A lettuce hydroponic culture, grown for 36 days, was exposed to metformin, acetaminophen and carbamazepine (at 1 mg/L), during 8 days, after which roots and leaves were sampled and analysed using a liquid chromatography-mass spectrometry proteomics-based approach. In roots, a total of 612 proteins showed differentially accumulation while in leaves 237 proteins were identified with significant differences over controls. Carbamazepine was the contaminant that most affected protein abundance in roots, while in leaves the highest number of differentially accumulated proteins was observed for acetaminophen. In roots under carbamazepine, stress related protein species such as catalase, superoxide dismutase and peroxidases presented higher abundance. Ascorbate peroxidase increased in roots under metformin. Cell respiration protein species were affected by the presence of the three pharmaceuticals suggesting possible dysregulation of the Krebs cycle. Acetaminophen caused the main differences in respiration pathways, with more emphasis in leaves. Lettuce plants revealed different tolerance levels when contaminants were compared, being more tolerant to metformin presence and less tolerant to carbamazepine. SIGNIFICANCE: The significant increase of emerging contaminants in ecosystems makes essential to understand how these compounds may affect the metabolism of different organisms. Our study contributes with a detailed approach of the main interactions that may occur in plant metabolism when subjected to the stress induced by three different pharmaceuticals (acetaminophen, carbamazepine and metformin).

The Resistance of Oilseed Rape Microspore-Derived Embryos to Osmotic Stress Is Associated With the Accumulation of Energy Metabolism Proteins, Redox Homeostasis, Higher Abscisic Acid, and Cytokinin Contents

The present study aims to investigate the response of rapeseed microspore-derived embryos (MDE) to osmotic stress at the proteome level. The PEG-induced osmotic stress was studied in the cotyledonary stage of MDE of two genotypes: Cadeli (D) and Viking (V), previously reported to exhibit contrasting leaf proteome responses under drought. Two-dimensional difference gel electrophoresis (2D-DIGE) revealed 156 representative protein spots that have been selected for MALDI-TOF/TOF analysis. Sixty-three proteins have been successfully identified and divided into eight functional groups. Data are available via ProteomeXchange with identifier PXD024552. Eight selected protein accumulation trends were compared with real-time quantitative PCR (RT-qPCR). Biomass accumulation in treated D was significantly higher (3-fold) than in V, which indicates D is resistant to osmotic stress. Cultivar D displayed resistance strategy by the accumulation of proteins in energy metabolism, redox homeostasis, protein destination, and signaling functional groups, high ABA, and active cytokinins (CKs) contents. In contrast, the V protein profile displayed high requirements of energy and nutrients with a significant number of stress-related proteins and cell structure changes accompanied by quick downregulation of active CKs, as well as salicylic and jasmonic acids. Genes that were suitable for gene-targeting showed significantly higher expression in treated samples and were identified as phospholipase D alpha, peroxiredoxin antioxidant, and lactoylglutathione lyase. The MDE proteome profile has been compared with the leaf proteome evaluated in our previous study. Different mechanisms to cope with osmotic stress were revealed between the genotypes studied. This proteomic study is the first step to validate MDE as a suitable model for follow-up research on the characterization of new crossings and can be used for preselection of resistant genotypes.

iTRAQ-based quantitative proteomic analysis of heat stress-induced mechanisms in pepper seedlings

Background

As one of the most important vegetable crops, pepper has rich nutritional value and high economic value. Increasing heat stress due to the global warming has a negative impact on the growth and yield of pepper.

Methods

To understand the heat stress response mechanism of pepper, an iTRAQ-based quantitative proteomic analysis was employed to identify possible heat-responsive proteins and metabolic pathways in 17CL30 and 05S180 pepper seedlings under heat stress.

Result

In the present study, we investigated the changes of phenotype, physiology, and proteome in heat-tolerant (17CL30) and heat-sensitive (05S180) pepper cultivars in response to heat stress. Phenotypic and physiological changes showed that 17CL30 had a stronger ability to resist heat stress compared with 05S180. In proteomic analysis, a total of 3,874 proteins were identified, and 1,591 proteins were considered to participate in the process of heat stress response. According to bioinformatic analysis of heat-responsive proteins, the heat tolerance of 17CL30 might be related to a higher ROS scavenging, photosynthesis, signal transduction, carbohydrate metabolism, and stress defense, compared with 05S180.

Assessment of Acidic Biochar on the Growth, Physiology and Nutrients Uptake of Maize (Zea mays L.) Seedlings under Salinity Stress

The application of an acidic biochar can improve plant growth and soil properties in saline conditions. In this study, we investigated the effect of acidic biochar on plant growth and nutrients contents in saline soil. Seven treatments were arranged in a complete randomized design, including control (CK), 0, 30, and 45 g biochar added to a soil having 1% and 1.5% salts; these treatments were termed as B0S1, B30S1, B45S1 and B0S1.5, B30S1.5, B45S1.5 respectively. Experimental results showed that the plant height, leaves plant−1, leaf area, and shoot fresh and dry biomass, and root fresh and dry biomass were increased for the B45S1.5, respectively. Similarly, the highest total nitrogen (TN), total phosphorus (TP), total potassium (TK), and total sodium (Na) concentration in maize shoot were observed for B30S1, B0S1.5, CK, and B0S1.5, respectively. The highest concentrations of TN, TP, TK, and Na in root were obtained with the treatments B0S1, B0S1, B45S1, and B0S1, respectively. Soil pH, and EC decreased and nutrients concentration improved by the addition of acidic biochar. We conclude that the use of acidic biochar can be a potential source for the improvement of maize plant growth as well as mitigate the adverse effect of salt stress.

Enhanced Abiotic Stress Tolerance of Vicia faba L. Plants Heterologously Expressing the PR10a Gene from Potato

Pathogenesis-related (PR) proteins are known to play relevant roles in plant defense against biotic and abiotic stresses. In the present study, we characterize the response of transgenic faba bean (Vicia faba L.) plants encoding a PR10a gene from potato (Solanum tuberosum L.) to salinity and drought. The transgene was under the mannopine synthetase (pMAS) promoter. PR10a-overexpressing faba bean plants showed better growth than the wild-type plants after 14 days of drought stress and 30 days of salt stress under hydroponic growth conditions. After removing the stress, the PR10a-plants returned to a normal state, while the wild-type plants could not be restored. Most importantly, there was no phenotypic difference between transgenic and non-transgenic faba bean plants under well-watered conditions. Evaluation of physiological parameters during salt stress showed lower Na⁺-content in the leaves of the transgenic plants, which would reduce the toxic effect. In addition, PR10a-plants were able to maintain vegetative growth and experienced fewer photosystem changes under both stresses and a lower level of osmotic stress injury under salt stress compared to wild-type plants. Taken together, our findings suggest that the PR10a gene from potato plays an important role in abiotic stress tolerance, probably by activation of stress-related physiological processes.

Plant endophytes promote growth and alleviate salt stress in Arabidopsis thaliana

Plant growth promoting rhizobacteria (PGPR) are a functionally diverse group of microbes having immense potential as biostimulants and stress alleviators. Their exploitation in agro-ecosystems as an eco-friendly and cost-effective alternative to traditional chemical inputs may positively affect agricultural productivity and environmental sustainability. The present study describes selected rhizobacteria, from a range of origins, having plant growth promoting potential under controlled conditions. A total of 98 isolates (ectophytic or endophytic) from various crop and uncultivated plants were screened, out of which four endophytes (n, L, K and Y) from Phalaris arundinacea, Solanum dulcamara, Scorzoneroides autumnalis, and Glycine max, respectively, were selected in vitro for their vegetative growth stimulating effects on Arabidopsis thaliana Col-0 seedlings with regard to leaf surface area and shoot fresh weight. A 16S rRNA gene sequencing analysis of the strains indicated that these isolates belong to the genera Pseudomonas, Bacillus, Mucilaginibacter and Rhizobium. Strains were then further tested for their effects on abiotic stress alleviation under both Petri-plate and pot conditions. Results from Petri-dish assay indicated strains L, K and Y alleviated salt stress in Arabidopsis seedlings, while strains K and Y conferred increases in fresh weight and leaf area under osmotic stress. Results from subsequent in vivo trials indicated all the isolates, especially strains L, K and Y, distinctly increased A. thaliana growth under both normal and high salinity conditions, as compared to control plants. The activity of antioxidant enzymes (ascorbate peroxidase, catalase and peroxidase), proline content and total antioxidative capacity also differed in the inoculated A. thaliana plants. Furthermore, a study on spatial distribution of the four strains, using either conventional Petri-plate counts or GFP-tagged bacteria, indicated that all four strains were able to colonize the endosphere of A. thaliana root tissue. Thus, the study revealed that the four selected rhizobacteria are good candidates to be explored as plant growth stimulators, which also possess salt stress mitigating property, partially by regulating osmolytes and antioxidant enzymes. Moreover, the study is the first report of Scorzoneroides autumnalis (fall dandelion) and Solanum dulcamara (bittersweet) associated endophytes with PGP effects.

Comparing transcriptome expression profiles to reveal the mechanisms of salt tolerance and exogenous glycine betaine mitigation in maize seedlings

Salt stress is a common abiotic stress that limits the growth, development and yield of maize (Zea mays L.). To better understand the response of maize to salt stress and the mechanism by which exogenous glycine betaine (GB) alleviates the damaging effects of salt stress, the morphology, physiological and biochemical indexes, and root transcriptome expression profiles of seedlings of salt-sensitive inbred line P138 and salt-tolerant inbred line 8723 were compared under salt stress and GB-alleviated salt stress conditions. The results showed that under salt stress the growth of P138 was significantly inhibited and the vivo ion balance was disrupted, whereas 8723 could prevent salt injury by maintaining a high ratio of K+ to Na+. The addition of a suitable concentration of GB could effectively alleviate the damage caused by salt stress, and the mitigating effect on salt-sensitive inbred line P138 was more obvious than that on 8723. Transcriptome analysis revealed that 219 differentially expressed genes (DEGs) were up-regulated and 153 DEGs were down-regulated in both P138 and 8723 under NaCl treatment, and that 487 DEGs were up-regulated and 942 DEGs were down-regulated in both P138 and 8723 under salt plus exogenous GB treatment. In 8723 the response to salt stress is mainly achieved through stabilizing ion homeostasis, strong signal transduction activation, increasing reactive oxygen scavenging. GB alleviates salt stress in maize mainly by inducing gene expression changes to enhance the ion balance, secondary metabolic level, reactive oxygen scavenging mechanism, signal transduction activation. In addition, the transcription factors involved in the regulation of salt stress response and exogenous GB mitigation mainly belong to the MYB, MYB-related, AP2-EREBP, bHLH, and NAC families. We verified 10 selected up-regulated DEGs by quantitative real-time polymerase chain reaction (qRT-PCR), and the expression results were basically consistent with the transcriptome expression profiles. Our results from this study may provide the theoretical basis for determining maize salt tolerance mechanisms and the mechanism by which GB regulates salt tolerance.

NaCl-responsive ROS scavenging and energy supply in alkaligrass callus revealed from proteomic analysis

BACKGROUND

Salinity has obvious effects on plant growth and crop productivity. The salinity-responsive mechanisms have been well-studied in differentiated organs (e.g., leaves, roots and stems), but not in unorganized cells such as callus. High-throughput quantitative proteomics approaches have been used to investigate callus development, somatic embryogenesis, organogenesis, and stress response in numbers of plant species. However, they have not been applied to callus from monocotyledonous halophyte alkaligrass (Puccinellia tenuifora).

RESULTS

The alkaligrass callus growth, viability and membrane integrity were perturbed by 50 mM and 150 mM NaCl treatments. Callus cells accumulated the proline, soluble sugar and glycine betaine for the maintenance of osmotic homeostasis. Importantly, the activities of ROS scavenging enzymes (e.g., SOD, APX, POD, GPX, MDHAR and GR) and antioxidants (e.g., ASA, DHA and GSH) were induced by salinity. The abundance patterns of 55 salt-responsive proteins indicate that salt signal transduction, cytoskeleton, ROS scavenging, energy supply, gene expression, protein synthesis and processing, as well as other basic metabolic processes were altered in callus to cope with the stress.

CONCLUSIONS

The undifferentiated callus exhibited unique salinity-responsive mechanisms for ROS scavenging and energy supply. Activation of the POD pathway and AsA-GSH cycle was universal in callus and differentiated organs, but salinity-induced SOD pathway and salinity-reduced CAT pathway in callus were different from those in leaves and roots. To cope with salinity, callus mainly relied on glycolysis, but not the TCA cycle, for energy supply.

iTRAQ-Based Proteomic Analysis Reveals Several Strategies to Cope with Drought Stress in Maize Seedlings

Drought stress, especially during the seedling stage, seriously limits the growth of maize and reduces production in the northeast of China. To investigate the molecular mechanisms of drought response in maize seedlings, proteome changes were analyzed. Using an isotopic tagging relative quantitation (iTRAQ) based method, a total of 207 differentially accumulated protein species (DAPS) were identified under drought stress in maize seedlings. The DAPS were classified into ten essential groups and analyzed thoroughly, which involved in signaling, osmotic regulation, protein synthesis and turnover, reactive oxygen species (ROS) scavenging, membrane trafficking, transcription related, cell structure and cell cycle, fatty acid metabolism, carbohydrate and energy metabolism, as well as photosynthesis and photorespiration. The enhancements of ROS scavenging, osmotic regulation, protein turnover, membrane trafficking, and photosynthesis may play important roles in improving drought tolerance of maize seedlings. Besides, the inhibitions of some protein synthesis and slowdown of cell division could reduce the growth rate and avoid excessive water loss, which is possible to be the main reasons for enhancing drought avoidance of maize seedlings. The incongruence between protein and transcript levels was expectedly observed in the process of confirming iTRAQ data by quantitative real-time polymerase chain reaction (qRT-PCR) analysis, which further indicated that the multiplex post-transcriptional regulation and post-translational modification occurred in drought-stressed maize seedlings. Finally, a hypothetical strategy was proposed that maize seedlings coped with drought stress by improving drought tolerance (via. promoting osmotic adjustment and antioxidant capacity) and enhancing drought avoidance (via. reducing water loss). Our study provides valuable insight to mechanisms underlying drought response in maize seedlings.

Comparative Proteomics of Salt-Tolerant and Salt-Sensitive Maize Inbred Lines to Reveal the Molecular Mechanism of Salt Tolerance

Salt stress is one of the key abiotic stresses that causes great loss of yield and serious decrease in quality in maize (Zea mays L.). Therefore, it is very important to reveal the molecular mechanism of salt tolerance in maize. To acknowledge the molecular mechanisms underlying maize salt tolerance, two maize inbred lines, including salt-tolerant 8723 and salt-sensitive P138, were used in this study. Comparative proteomics of seedling roots from two maize inbred lines under 180 mM salt stress for 10 days were performed by the isobaric tags for relative and absolute quantitation (iTRAQ) approach. A total of 1056 differentially expressed proteins (DEPs) were identified. In total, 626 DEPs were identified in line 8723 under salt stress, among them, 378 up-regulated and 248 down-regulated. There were 473 DEPs identified in P138, of which 212 were up-regulated and 261 were down-regulated. Venn diagram analysis showed that 17 DEPs were up-regulated and 12 DEPs were down-regulated in the two inbred lines. In addition, 8 DEPs were up-regulated in line 8723 but down-regulated in P138, 6 DEPs were down-regulated in line 8723 but up-regulated in P138. In salt-stressed 8723, the DEPs were primarily associated with phenylpropanoid biosynthesis, starch and sucrose metabolism, and the mitogen-activated protein kinase (MAPK) signaling pathway. Intriguingly, the DEPs were only associated with the nitrogen metabolism pathway in P138. Compared to P138, the root response to salt stress in 8723 could maintain stronger water retention capacity, osmotic regulation ability, synergistic effects of antioxidant enzymes, energy supply capacity, signal transduction, ammonia detoxification ability, lipid metabolism, and nucleic acid synthesis. Based on the proteome sequencing information, changes of 8 DEPs abundance were related to the corresponding mRNA levels by quantitative real-time PCR (qRT-PCR). Our results from this study may elucidate some details of salt tolerance mechanisms and salt tolerance breeding of maize.

Rhizobacteria AK1 remediates the toxic effects of salinity stress via regulation of endogenous phytohormones and gene expression in soybean

Salinity stress adversely affects the growth and productivity of different crops. In the present study, we isolated the rhizospheric bacteria Arthrobacter woluwensis AK1 from Pohang beach, South Korea and determined its plant growth-promoting potential under NaCl salt stress (0, 100, and 200 mM). AK1 has phosphate-solubilizing activity and produce siderophores, organic acids, and phytohormones such as gibberellic acid (GA) and indole-3-acetic acid (IAA) that significantly alleviate sodium chloride (NaCl) stress and increase all plant growth attributes. Furthermore, inoculation of AK1 significantly decreased endogenous abscisic acid (ABA) content, extensively regulated the antioxidant activities and mitigated NaCl stress. Similarly, inductively coupled plasma mass spectrometry results showed that soybean plants inoculated with AK1 significantly decreased the amount of sodium (Na+) uptake during NaCl stress after 6 and 12 days. Four genes, auxin resistant 1 (GmLAX1), potassium channel AKT2 (GmAKT2), soybean salt tolerance 1 (GmST1), and salt tolerance-associated gene on chromosome 3 (GmSALT3) were up-regulated, while two genes chloride channel gene (GmNHX1) and Na+/H+ antiporter (GmCLC1) were down-regulated in soybean AK1treated plants. In conclusion, AK1 can mitigate salinity stress, increase plant growth and could be utilized as an eco-friendly bio-fertilizer under salinity stress.

Proteomic Analysis of Rapeseed Root Response to Waterlogging Stress

The overall health of a plant is constantly affected by the changing and hostile environment. Due to climate change and the farming pattern of rice (Oryza sativa) and rapeseed (Brassica napus L.), stress from waterlogging poses a serious threat to productivity assurance and the yield of rapeseed in China's Yangtze River basin. In order to improve our understanding of the complex mechanisms behind waterlogging stress and identify waterlogging-responsive proteins, we firstly conducted iTRAQ (isobaric tags for relative and absolute quantification)-based quantitative proteomic analysis of rapeseed roots under waterlogging treatments, for both a tolerant cultivar ZS9 and sensitive cultivar GH01. A total of 7736 proteins were identified by iTRAQ, of which several hundred showed different expression levels, including 233, 365, and 326 after waterlogging stress for 4H, 8H, and 12H in ZS9, respectively, and 143, 175, and 374 after waterlogging stress for 4H, 8H, and 12H in GH01, respectively. For proteins repeatedly identified at different time points, gene ontology (GO) cluster analysis suggested that the responsive proteins of the two cultivars were both enriched in the biological process of DNA-dependent transcription and the oxidation⁻reduction process, and response to various stress and hormone stimulus, while different distribution frequencies in the two cultivars was investigated. Moreover, overlap proteins with similar or opposite tendencies of fold change between ZS9 and GH01 were observed and clustered based on the different expression ratios, suggesting the two genotype cultivars exhibited diversiform molecular mechanisms or regulation pathways in their waterlogging stress response. The following qRT-PCR (quantitative real-time polymerase chain reaction) results verified the candidate proteins at transcription levels, which were prepared for further research. In conclusion, proteins detected in this study might perform different functions in waterlogging responses and would provide information conducive to better understanding adaptive mechanisms under environmental stresses.

The partial root-zone saline irrigation system and antioxidant responses in tomato plants

Salinity is a limiting factor that can affect plant growth and cause significant losses in agricultural productivity. This study provides an insight about the viability of partial root-zone irrigation (PRI) system with saline water supported by a biochemical approach involving antioxidant responses. Six different irrigation methods using low and high salt concentrations (S1-0.5 and S2-5.0 dS m^-1) were applied, with or without PRSI, so that one side of the root-zone was submitted to saline water while the other side was low salinity water irrigated. The results revealed different responses according to the treatments and the PRSI system applied. For the treatments T1, T2 and T3, the PRSI was not applied, while T4, T5 and T6 treatments were applied with PRSI system. Lipid peroxidation, proline content, and activities of SOD, CAT, APX, GR and GSH in tomato plants subjected to PRSI system were analyzed. Plant growth was not affected by the salt concentrations; however, plants submitted to high salt concentrations showed high MDA content and Na⁺ accumulation when compared to the control plants. Plants submitted to treatments T4, T5 and T6 with PRSI system exhibited lower MDA compared to the control plants (T1). Proline content and activities of SOD, CAT, APX, GR and GSH content were maintained in all treatments and tissues analyzed, with only exception for APX in fruits and GSH content, in roots. The overall results showed that PRSI system could be an applicable technique for saline water supply on irrigation since plants did not show to be vulnerable to salt stress, supported by a biochemical approach involving antioxidant responses.

A Proteomic Approach to Investigate the Drought Response in the Orphan Crop Eragrostis tef

The orphan crop, Eragrostis tef, was subjected to controlled drought conditions to observe the physiological parameters and proteins changing in response to dehydration stress. Physiological measurements involving electrolyte leakage, chlorophyll fluorescence and ultra-structural analysis showed tef plants tolerated water loss to 50% relative water content (RWC) before adverse effects in leaf tissues were observed. Proteomic analysis using isobaric tag for relative and absolute quantification (iTRAQ) mass spectrometry and appropriate database searching enabled the detection of 5727 proteins, of which 211 proteins, including a number of spliced variants, were found to be differentially regulated with the imposed stress conditions. Validation of the iTRAQ dataset was done with selected stress-related proteins, fructose-bisphosphate aldolase (FBA) and the protective antioxidant proteins, monodehydroascorbate reductase (MDHAR) and peroxidase (POX). Western blot analyses confirmed protein presence and showed increased protein abundance levels during water deficit while enzymatic activity for FBA, MDHAR and POX increased at selected RWC points. Gene ontology (GO)-term enrichment and analysis revealed terms involved in biotic and abiotic stress response, signaling, transport, cellular homeostasis and pentose metabolic processes, to be enriched in tef upregulated proteins, while terms linked to reactive oxygen species (ROS)-producing processes under water-deficit, such as photosynthesis and associated light harvesting reactions, manganese transport and homeostasis, the synthesis of sugars and cell wall catabolism and modification, to be enriched in tef downregulated proteins.

Heat-Responsive Photosynthetic and Signaling Pathways in Plants: Insight from Proteomics

Heat stress is a major abiotic stress posing a serious threat to plants. Heat-responsive mechanisms in plants are complicated and fine-tuned. Heat signaling transduction and photosynthesis are highly sensitive. Therefore, a thorough understanding of the molecular mechanism in heat stressed-signaling transduction and photosynthesis is necessary to protect crop yield. Current high-throughput proteomics investigations provide more useful information for underlying heat-responsive signaling pathways and photosynthesis modulation in plants. Several signaling components, such as guanosine triphosphate (GTP)-binding protein, nucleoside diphosphate kinase, annexin, and brassinosteroid-insensitive I-kinase domain interacting protein 114, were proposed to be important in heat signaling transduction. Moreover, diverse protein patterns of photosynthetic proteins imply that the modulations of stomatal CO₂ exchange, photosystem II, Calvin cycle, ATP synthesis, and chlorophyll biosynthesis are crucial for plant heat tolerance.

Towards a better understanding of protein changes in common bean under drought: A case study of N-glycoproteins

Drought is one of the major abiotic stress conditions limiting crop growth and productivity. Glycosylation of proteins is very important post-translational modification that is involved in many physiological functions and biological pathways. To understand the involvement of N-glycoproteins in the mechanism of drought response in leaves of common bean, a proteomic approach using lectin affinity chromatography, SDS-PAGE and LC-MS/MS was applied. Quantification of N-glycoproteins was performed using MaxQuant with a label free quantification approach. Thirty five glycoproteins were changed in abundance in leaves of common bean under drought. The majority of these proteins were classified into functional groups that include cell wall processes, defence/stress related proteins and proteins related to proteolysis. Beta-glucosidase showed the highest increase in abundance among proteins involved in cell wall metabolism, suggesting its role in cell wall modification under drought stress. These results fit with the general concept of the stress response in plants and suggest that drought stress might affect biochemical metabolism in the cell wall. The structures of N-glycans were determined manually from spectra, where structures of high mannose, complex and hybrid types of N-glycans were found. The present study provided an insight into the glycoproteins related to drought stress in common bean at the proteome level, which is important for further understanding of molecular mechanisms of drought response in this important legume.

Potassium and zinc increase tolerance to salt stress in wheat (Triticum aestivum L.)

Potassium and zinc are essential elements in plant growth and metabolism and plays a vital role in salt stress tolerance. To investigate the physiological mechanism of salt stress tolerance, a pot experiment was conducted. Potassium and zinc significantly minimize the oxidative stress and increase root, shoot and spike length in wheat varieties. Fresh and dry biomass were significantly increased by potassium followed by zinc as compared to control C. The photosynthetic pigment and osmolyte regulator (proline, total phenolic, and total carbohydrate) were significantly enhanced by potassium and zinc. Salt stress increases MDA content in wheat varieties while potassium and zinc counteract the adverse effect of salinity and significantly increased membrane stability index. Salt stress decreases the activities of antioxidant enzymes (superoxide dismutase, catalase and ascorbate peroxidase) while the exogenous application of potassium and zinc significantly enhanced the activities of these enzymes. A significant positive correlation was found of spike length with proline (R² = 0.966 ^∗∗∗), phenolic (R² = 0.741^∗) and chlorophyll (R² = 0.853^∗∗). The MDA content showed significant negative correlation (R² = 0.983^∗∗∗) with MSI. It is concluded that potassium and zinc reduced toxic effect of salinity while its combine application showed synergetic effect and significantly enhanced salt tolerance.

Ectopic Expression of CDF3 Genes in Tomato Enhances Biomass Production and Yield under Salinity Stress Conditions

Cycling Dof Factor (CDF) transcription factors (TFs) are involved in multiple processes related to plant growth and development. A member of this family, CDF3, has recently been linked in Arabidopsis to the regulation of primary metabolism and abiotic stress responses, but its role in crop production under stress is still unknown. In this study, we characterized tomato plants overexpressing the CDF3 genes from Arabidopsis and tomato and analyzed their effects on growth and yield under salinity, additionally gaining deeper insights into the molecular function of these TFs. Our results provide evidence for higher biomass production and yield in the 35S::AtCDF3 and 35S::SlCDF3 plants, likely due to a higher photosynthetic capacity resulting in increased sucrose availability. Transcriptome analysis revealed that CDF3 genes regulate a set of genes involved in redox homeostasis, photosynthesis performance and primary metabolism that lead to enhanced biomass production. Consistently, metabolomic profiling revealed that CDF3 evokes changes in the primary metabolism triggering enhanced nitrogen assimilation, and disclosed that the amount of some protective metabolites including sucrose, GABA and asparagine were higher in vegetative tissues of CDF3 overexpressing plants. Altogether these changes improved performance of 35S::AtCDF3 and 35S::SlCDF3 plants under salinity conditions. Moreover, the overexpression of CDF3 genes modified organic acid and sugar content in fruits, improving variables related to flavor perception and fruit quality. Overall, our results associate the CDF3 TF with a role in the control of growth and C/N metabolism, and highlight that overexpression of CDF3 genes can substantially improve plant yield.

Proteomic analysis of common bean stem under drought stress using in-gel stable isotope labeling

Drought is an abiotic stress that strongly influences plant growth, development and productivity. Proteome changes in the stem of the drought-tolerant common bean (Phaseolus vulgaris L.) cultivar Tiber have were when the plants were exposed to drought. Five-week-old plants were subjected to water deficit by withholding irrigation for 7, 12 and 17days, whereas control plants were regularly irrigated. Relative water content (RWC) of leaves, as an indicator of the degree of cell and tissue hydration, showed the highest statistically significant differences between control and drought-stressed plants after 17days of treatment, where RWC remained at 90% for control and declined to 45% for stressed plants. Plants exposed to drought for 17days and control plants at the same developmental stage were included in quantitative proteomic analysis using in-gel stable isotope labeling of proteins in combination with mass spectrometry. The quantified proteins were grouped into several functional groups, mainly into energy metabolism, photosynthesis, proteolysis, protein synthesis and proteins related to defense and stress. 70kDa heat shock protein showed the greatest increase in abundance under drought of all the proteins, suggesting its role in protecting plants against stress by re-establishing normal protein conformations and thus cellular homeostasis. The abundance of proteins involved in protein synthesis also increased under drought stress, important for recovery of damaged proteins involved in the plant cell's metabolic activities. Other important proteins in this study were related to proteolysis and folding, which are necessary for maintaining proper cellular protein homeostasis. Taken together, these results reveal the complexity of pathways involved in the drought stress response in common bean stems and enable comparison with the results of proteomic analysis of leaves, thus providing important information to further understand the biochemical and molecular mechanisms of drought response in this important legume.

Effects of microcystin-LR and cylindrospermopsin on plant-soil systems: A review of their relevance for agricultural plant quality and public health

Toxic cyanobacterial blooms are recognized as an emerging environmental threat worldwide. Although microcystin-LR is the most frequently documented cyanotoxin, studies on cylindrospermopsin have been increasing due to the invasive nature of cylindrospermopsin-producing cyanobacteria. The number of studies regarding the effects of cyanotoxins on agricultural plants has increased in recent years, and it has been suggested that the presence of microcystin-LR and cylindrospermopsin in irrigation water may cause toxic effects in edible plants. The uptake of these cyanotoxins by agricultural plants has been shown to induce morphological and physiological changes that lead to a potential loss of productivity. There is also evidence that edible terrestrial plants can bioaccumulate cyanotoxins in their tissues in a concentration dependent-manner. Moreover, the number of consecutive cycles of watering and planting in addition to the potential persistence of microcystin-LR and cylindrospermopsin in the environment are likely to result in groundwater contamination. The use of cyanotoxin-contaminated water for agricultural purposes may therefore represent a threat to both food security and food safety. However, the deleterious effects of cyanotoxins on agricultural plants and public health seem to be dependent on the concentrations studied, which in most cases are non-environmentally relevant. Interestingly, at ecologically relevant concentrations, the productivity and nutritional quality of some agricultural plants seem not to be impaired and may even be enhanced. However, studies assessing if the potential tolerance of agricultural plants to these concentrations can result in cyanotoxin and allergen accumulation in the edible tissues are lacking. This review combines the most current information available regarding this topic with a realistic assessment of the impact of cyanobacterial toxins on agricultural plants, groundwater quality and public health.

Analysis of Soluble Proteins in Natural Cordyceps sinensis from Different Producing Areas by Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis and Two-dimensional Electrophoresis

Background:

As one of the bioactive components in Cordyceps sinensis (CS), proteins were rarely used as index components to study the correlation between the protein components and producing areas of natural CS.

Objective:

Protein components of 26 natural CS samples produced in Qinghai, Tibet, and Sichuan provinces were analyzed and compared to investigate the relationship among 26 different producing areas.

Materials and Methods:

Proteins from 26 different producing areas were extracted by Tris-HCl buffer with Triton X-100, and separated using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and two-dimensional electrophoresis (2-DE).

Results:

The SDS-PAGE results indicated that the number of protein bands and optical density curves of proteins in 26 CS samples was a bit different. However, the 2-DE results showed that the numbers and abundance of protein spots in protein profiles of 26 samples were obviously different and showed certain association with producing areas.

Conclusions:

Based on the expression values of matched protein spots, 26 batches of CS samples can be divided into two main categories (Tibet and Qinghai) by hierarchical cluster analysis.

SUMMARY

The number of protein bands and optical density curves of proteins in 26 Cordyceps sinensis samples were a bit different on the sodium dodecyl sulfate-polyacrylamide gel electrophoresis protein profiles

Numbers and abundance of protein spots in protein profiles of 26 samples were obvious different on two-dimensional electrophoresis maps

Twenty-six different producing areas of natural Cordyceps sinensis samples were divided into two main categories (Tibet and Qinghai) by Hierarchical cluster analysis based on the values of matched protein spots.

Abbreviations Used: SDS-PAGE: Sodium dodecyl sulfate polyacrylamide gel electrophoresis, 2-DE: Two-dimensional electrophoresis, Cordyceps sinensis: CS, TCMs: Traditional Chinese medicines

Proteomic and physiological approach reveals drought-induced changes in rapeseeds: Water-saver and water-spender strategy

The cultivar-dependent differences in Brassica napus L. seed yield are significantly affected by drought stress. Here, the response of leaf proteome to long-term drought (28days) was studied in cultivars (cvs): Californium (C), Cadeli (D), Navajo (N), and Viking (V). Analysis of twenty-four 2-D DIGE gels revealed 134 spots quantitatively changed at least 2-fold; from these, 79 proteins were significantly identified by MALDI-TOF/TOF. According to the differences in water use, the cultivars may be assigned to two categories: water-savers or water-spenders. In the water-savers group (cvs C+D), proteins related to nitrogen assimilation, ATP and redox homeostasis were increased under stress, while in the water-spenders category (cvs N+V), carbohydrate/energy, photosynthesis, stress related and rRNA processing proteins were increased upon stress. Taking all data together, we indicated cv C as a drought-adaptable water-saver, cv D as a medium-adaptable water-saver, cv N as a drought-adaptable water-spender, and cv V as a low-adaptable drought sensitive water-spender rapeseed. Proteomic data help to evaluate the impact of drought and the extent of genotype-based adaptability and contribute to the understanding of their plasticity. These results provide new insights into the provenience-based drought acclimation/adaptation strategy of contrasting winter rapeseeds and link data at gasometric, biochemical, and proteome level.

SIGNIFICANCE

Soil moisture deficit is a real problem for every crop. The data in this study demonstrates for the first time that in stem-prolongation phase cultivars respond to progressive drought in different ways and at different levels. Analysis of physiological and proteomic data showed two different water regime-related strategies: water-savers and spenders. However, not only water uptake rate itself, but also individual protein abundances, gasometric and biochemical parameters together with final biomass accumulation after stress explained genotype-based responses. Interestingly, under a mixed climate profile, both water-use patterns (savers or spenders) can be appropriate for drought adaptation. These data suggest, than complete "acclimation image" of rapeseeds in stem-prolongation phase under drought could be reached only if these characteristics are taken, explained and understood together.

Drought-Responsive Mechanisms in Plant Leaves Revealed by Proteomics

Plant drought tolerance is a complex trait that requires a global view to understand its underlying mechanism. The proteomic aspects of plant drought response have been extensively investigated in model plants, crops and wood plants. In this review, we summarize recent proteomic studies on drought response in leaves to reveal the common and specialized drought-responsive mechanisms in different plants. Although drought-responsive proteins exhibit various patterns depending on plant species, genotypes and stress intensity, proteomic analyses show that dominant changes occurred in sensing and signal transduction, reactive oxygen species scavenging, osmotic regulation, gene expression, protein synthesis/turnover, cell structure modulation, as well as carbohydrate and energy metabolism. In combination with physiological and molecular results, proteomic studies in leaves have helped to discover some potential proteins and/or metabolic pathways for drought tolerance. These findings provide new clues for understanding the molecular basis of plant drought tolerance.

High Salinity Induces Different Oxidative Stress and Antioxidant Responses in Maize Seedlings Organs

Salinity negatively affects plant growth and causes significant crop yield losses world-wide. Maize is an economically important cereal crop affected by high salinity. In this study, maize seedlings were subjected to 75 mM and 150 mM NaCl, to emulate high soil salinity. Roots, mature leaves (basal leaf-pair 1,2) and young leaves (distal leaf-pair 3,4) were harvested after 3 weeks of sowing. Roots showed the highest reduction in biomass, followed by mature and young leaves in the salt-stressed plants. Concomitant with the pattern of growth reduction, roots accumulated the highest levels of Na(+) followed by mature and young leaves. High salinity induced oxidative stress in the roots and mature leaves, but to a lesser extent in younger leaves. The younger leaves showed increased electrolyte leakage (EL), malondialdehyde (MDA), and hydrogen peroxide (H2O2) concentrations only at 150 mM NaCl. Total antioxidant capacity (TAC) and polyphenol content increased with the increase in salinity levels in roots and mature leaves, but showed no changes in the young leaves. Under salinity stress, reduced ascorbate (ASC) and glutathione (GSH) content increased in roots, while total tocopherol levels increased specifically in the shoot tissues. Similarly, redox changes estimated by the ratio of redox couples (ASC/total ascorbate and GSH/total glutathione) showed significant decreases in the roots. Activities of enzymatic antioxidants, catalase (CAT, EC 1.11.1.6) and dehydroascorbate reductase (DHAR, EC 1.8.5.1), increased in all organs of salt-treated plants, while superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), glutathione-s-transferase (GST, EC 2.5.1.18) and glutathione reductase (GR, EC 1.6.4.2) increased specifically in the roots. Overall, these results suggest that Na(+) is retained and detoxified mainly in roots, and less stress impact is observed in mature and younger leaves. This study also indicates a possible role of ROS in the systemic signaling from roots to leaves, allowing leaves to activate their defense mechanisms for better protection against salt stress.

Metabolic response of maize plants to multi-factorial abiotic stresses

Clarification of the metabolic mechanisms underlying multi-stress responses in plants will allow further optimisation of crop breeding and cultivation to obtain high yields in an increasingly variable environment. Using NMR metabolomic techniques, we examined the metabolic responses of maize plants grown under different conditions: soil drought, soil salinity, heat and multiple concurrent stresses. A detailed time-course metabolic profile was also performed on maize plants sampled 1, 3 and 7 days after initiation of soil drought and heat stress. The metabolic profile of maize plants subjected to soil drought was more similar to plants exposed to salt stress than to heat-stressed plants. Drought-stressed maize plants subjected to salt or heat stress showed distinct integrated metabolic profiles compared with those exposed to either stressor individually. These differences show the considerable metabolic plasticity of maize in response to different growth conditions. Moreover, glucose, fructose, malate, citrate, proline, alanine, aspartate, asparagine, threonine and one unknown compound fluctuated obviously between maize plants grown in controlled growth cabinet and a natural regime. These changes were associated with the TCA cycle and core nitrogen metabolism, and could be related to their multiple functions during plant growth. The evident stress-induced trajectory of metabolic changes in maize indicated that the primary metabolic responses to soil drought, heat and combined drought and heat stresses occurred in a time-dependent manner. Plasticity at the metabolic level may allow maize plants to acclimatise their metabolic ranges in response to changing environmental conditions.

Spinach (Spinacia oleracea L.) modulates its proteome differentially in response to salinity, cadmium and their combination stress

Cadmium (Cd) contamination and salinity are common stressors in agricultural soils all over the globe. Sensitivity and modulation of plant proteome lead to proper signal execution and adaptation to abiotic stress via molecular responses, which strengthen plant defence system. A comparative proteomic study, employing 2DE-MALDI TOF/TOF MS, of Spinacia oleracea plants exposed to cadmium (50 μg CdCl2 g(-1) soil), salinity (10 mg NaCl g(-1) soil) and their combination (NaCl + Cd) was conducted to understand the minimum common adaptation to multiple stress. Analysis of 2D gel maps showed significant increase and decrease in relative abundance of 14 and 39 proteins by Cd; 11 and 46 by salinity and 22 and 37 by combined stress of Cd and salinity, respectively. Peptide mass fingerprinting (PMF) helped in the identification of maturase K and PPD4 with increased relative abundance under all stresses; whereas salinity stress and combination stress silenced the presence of one protein (polycomb protein EZ2) and two proteins (cellulose synthase-like protein and ubiquitin conjugation factor E4), respectively. The identified proteins were functionally associated with signal transduction (15%), protein synthesis (16%), stress response and defence (33%), photosynthesis (13%), plant growth/cell division (9%), energy generation (4%), transport (4%), secondary metabolism (3%), and cell death (3%); clearly indicating the importance and necessity of keeping a higher ratio of defence and disease-responsive proteins. The results suggest that plant may increase the abundance of defence proteins and may also lower the abundance of catabolic proteins. Proteins with altered ratios of abundance belonged to different functional categories, suggesting that plants have differential mechanisms to respond to Cd, salinity, and their combined stress, but with unique sets of proteins.

Comparative study of the protein profiles of Sunki mandarin and Rangpur lime plants in response to water deficit

BACKGROUND

Rootstocks play a major role in the tolerance of citrus plants to water deficit by controlling and adjusting the water supply to meet the transpiration demand of the shoots. Alterations in protein abundance in citrus roots are crucial for plant adaptation to water deficit. We performed two-dimensional electrophoresis (2-DE) separation followed by LC/MS/MS to assess the proteome responses of the roots of two citrus rootstocks, Rangpur lime (Citrus limonia Osbeck) and 'Sunki Maravilha' (Citrus sunki) mandarin, which show contrasting tolerances to water deficits at the physiological and molecular levels.

RESULTS

Changes in the abundance of 36 and 38 proteins in Rangpur lime and 'Sunki Maravilha' mandarin, respectively, were observed via LC/MS/MS in response to water deficit. Multivariate principal component analysis (PCA) of the data revealed major changes in the protein profile of 'Sunki Maravilha' in response to water deficit. Additionally, proteomics and systems biology analyses allowed for the general elucidation of the major mechanisms associated with the differential responses to water deficit of both varieties. The defense mechanisms of Rangpur lime included changes in the metabolism of carbohydrates and amino acids as well as in the activation of reactive oxygen species (ROS) detoxification and in the levels of proteins involved in water stress defense. In contrast, the adaptation of 'Sunki Maravilha' to stress was aided by the activation of DNA repair and processing proteins.

CONCLUSIONS

Our study reveals that the levels of a number of proteins involved in various cellular pathways are affected during water deficit in the roots of citrus plants. The results show that acclimatization to water deficit involves specific responses in Rangpur lime and 'Sunki Maravilha' mandarin. This study provides insights into the effects of drought on the abundance of proteins in the roots of two varieties of citrus rootstocks. In addition, this work allows for a better understanding of the molecular basis of the response to water deficit in citrus. Further analysis is needed to elucidate the behaviors of the key target proteins involved in this response.