The oxygen evolving enhancer protein 1 (OEE) of photosystem II in green algae exhibits thioredoxin activity

Enhanced azadirachtin production in neem (Azadirachta indica) callus through NaCl elicitation: Insights into differential protein regulation via shotgun proteomics

With their remarkable bioactivity and evolving commercial importance, plant secondary metabolites (PSMs) have gained significant research interest in recent years. Plant tissue culture serves as a credible tool to examine how abiotic stresses modulate the production of PSMs, enabling clear insights into plant stress responses and the prospects for controlled synthesis of bioactive compounds. Azadirachta indica, or neem has been recognized as a repository of secondary metabolites for centuries, particularly for the compound named azadirachtin, due to its bio-pesticidal and high antioxidant properties. Introducing salt stress as an elicitor makes it possible to enhance the synthesis of secondary metabolites, specifically azadirachtin. Thus, in this research, in vitro callus cultures of neem were micro-propagated and induced with salinity stress to explore their effects on the production of azadirachtin and identify potential proteins associated with salinity stress through comparative shotgun proteomics (LCMS/MS). To induce salinity stress, 2-month-old calli were subjected to various concentrations of NaCl (0.05-1.5%) for 4 weeks. The results showed that the callus cultures were able to adapt and survive in the salinity treatments, but displayed a reduction in fresh weight as the NaCl concentration increased. Notably, azadirachtin production was significantly enhanced in the salinity treatment compared to control, where 1.5% NaCl-treated calli produced the highest azadirachtin amount (10.847 ± 0.037 mg/g DW). The proteomics analysis showed that key proteins related to primary metabolism, such as defence, energy, cell structure, redox, transcriptional and photosynthesis, were predominantly differentially regulated (36 upregulated and 93 downregulated). While a few proteins were identified as being regulated in secondary metabolism, they were not directly involved in the synthesis of azadirachtin. In conjunction with azadirachtin elicitation, salinity stress treatment could therefore be successfully applied in commercial settings for the controlled synthesis of azadirachtin and other plant-based compounds. Further complementary omics approaches can be employed to enhance molecular-level modifications, to facilitate large-scale production of bioactive compounds in the future.

Proteomics for abiotic stresses in legumes: present status and future directions

Legumes are the most important crop plants in agriculture, contributing 27% of the world's primary food production. However, productivity and production of Legumes is reduced due to increasing environmental stress. Hence, there is a pressing need to understand the molecular mechanism involved in stress response and legumes adaptation. Proteomics provides an important molecular approach to investigate proteins involved in stress response. Both the gel-based and gel-free-based techniques have significantly contributed to understanding the proteome regulatory network in leguminous plants. In the present review, we have discussed the role of different proteomic approaches (2-DE, 2 D-DIGE, ICAT, iTRAQ, etc.) in the identification of various stress-responsive proteins in important leguminous crops, including soybean, chickpea, cowpea, pigeon pea, groundnut, and common bean under variable abiotic stresses including heat, drought, salinity, waterlogging, frost, chilling and metal toxicity. The proteomic analysis has revealed that most of the identified differentially expressed proteins in legumes are involved in photosynthesis, carbohydrate metabolism, signal transduction, protein metabolism, defense, and stress adaptation. The proteomic approaches provide insights in understanding the molecular mechanism of stress tolerance in legumes and have resulted in the identification of candidate genes used for the genetic improvement of plants against various environmental stresses. Identifying novel proteins and determining their expression under different stress conditions provide the basis for effective engineering strategies to improve stress tolerance in crop plants through marker-assisted breeding.

Identification of genetic and biochemical mechanisms associated with heat shock and heat stress adaptation in grain amaranths

Heat stress is poised to become a major factor negatively affecting plant performance worldwide. In terms of world food security, increased ambient temperatures are poised to reduce yields in cereals and other economically important crops. Grain amaranths are known to be productive under poor and/or unfavorable growing conditions that significantly affect cereals and other crops. Several physiological and biochemical attributes have been recognized to contribute to this favorable property, including a high water-use efficiency and the activation of a carbon starvation response. This study reports the behavior of the three grain amaranth species to two different stress conditions: short-term exposure to heat shock (HS) conditions using young plants kept in a conditioned growth chamber or long-term cultivation under severe heat stress in greenhouse conditions. The latter involved exposing grain amaranth plants to daylight temperatures that hovered around 50°C, or above, for at least 4 h during the day and to higher than normal nocturnal temperatures for a complete growth cycle in the summer of 2022 in central Mexico. All grain amaranth species showed a high tolerance to HS, demonstrated by a high percentage of recovery after their return to optimal growing conditions. The tolerance observed coincided with increased expression levels of unknown function genes previously shown to be induced by other (a)biotic stress conditions. Included among them were genes coding for RNA-binding and RNA-editing proteins, respectively. HS tolerance was also in accordance with favorable changes in several biochemical parameters usually induced in plants in response to abiotic stresses. Conversely, exposure to a prolonged severe heat stress seriously affected the vegetative and reproductive development of all three grain amaranth species, which yielded little or no seed. The latter data suggested that the usually stress-tolerant grain amaranths are unable to overcome severe heat stress-related damage leading to reproductive failure.

Proteomics approach to investigating osmotic stress effects on pistachio

Osmotic stress can occur due to some stresses such as salinity and drought, threatening plant survival. To investigate the mechanism governing the pistachio response to this stress, the biochemical alterations and protein profile of PEG-treated plants was monitored. Also, we selected two differentially abundant proteins to validate via Real-Time PCR. Biochemical results displayed that in treated plants, proline and phenolic content was elevated, photosynthetic pigments except carotenoid decreased and MDA concentration were not altered. Our findings identified a number of proteins using 2DE-MS, involved in mitigating osmotic stress in pistachio. A total of 180 protein spots were identified, of which 25 spots were altered in response to osmotic stress. Four spots that had photosynthetic activities were down-regulated, and the remaining spots were up-regulated. The biological functional analysis of protein spots exhibited that most of them are associated with the photosynthesis and metabolism (36%) followed by stress response (24%). Results of Real-Time PCR indicated that two of the representative genes illustrated a positive correlation among transcript level and protein expression and had a similar trend in regulation of gene and protein. Osmotic stress set changes in the proteins associated with photosynthesis and stress tolerance, proteins associated with the cell wall, changes in the expression of proteins involved in DNA and RNA processing occur. Findings of this research will introduce possible proteins and pathways that contribute to osmotic stress and can be considered for improving osmotic tolerance in pistachio.

Multi-Approach Analysis Reveals Pathways of Cold Tolerance Divergence in Camellia japonica

Understanding the molecular mechanism of the cold response is critical to improve horticultural plant cold tolerance. Here, we documented the physiological, transcriptome, proteome, and hormonal dynamics to cold stress in temperate genotype (Tg) and subtropical genotype (Sg) populations of Camellia japonica. Tg C. japonica suffered minimal osmotic and oxidative damage compared to Sg C. japonica under the same cold treatment. Transcriptional and translational differences increased under the cold treatment, indicating that Tg C. japonica was affected by the environment and displayed both conserved and divergent mechanisms. About 60% of the genes responding to cold had similar dynamics in the two populations, but 1,896 transcripts and 455 proteins differentially accumulated in response to the cold between Tg and Sg C. japonica. Co-expression analysis showed that the ribosomal protein and genes related to photosynthesis were upregulated in Tg C. japonica, and tryptophan, phenylpropanoid, and flavonoid metabolism were regulated differently between the two populations under cold stress. The divergence of these genes reflected a difference in cold responsiveness. In addition, the decrease in the abscisic acid (ABA)/gibberellic acid (GA) ratio regulated by biosynthetic signal transduction pathway enhanced cold resistance in Tg C. japonica, suggesting that hormones may regulate the difference in cold responsiveness. These results provide a new understanding of the molecular mechanism of cold stress and will improve cold tolerance in horticultural plants.

Physiological and Proteomic Responses of Contrasting Alfalfa (Medicago sativa L.) Varieties to High Temperature Stress

High temperature (HT) is an important factor for limiting global plant distribution and agricultural production. As the global temperature continues to rise, it is essential to clarify the physiological and molecular mechanisms of alfalfa responding the high temperature, which will contribute to the improvement of heat resistance in leguminous crops. In this study, the physiological and proteomic responses of two alfalfa (Medicago sativa L.) varieties contrasting in heat tolerance, MS30 (heat-tolerant) and MS37 (heat-sensitive), were comparatively analyzed under the treatments of continuously rising temperatures for 42 days. The results showed that under the HT stress, the chlorophyll content and the chlorophyll fluorescence parameter (Fv/Fm) of alfalfa were significant reduced and some key photosynthesis-related proteins showed a down-regulated trend. Moreover, the content of Malondialdehyde (MDA) and the electrolyte leakage (EL) of alfalfa showed an upward trend, which indicates both alfalfa varieties were damaged under HT stress. However, because the antioxidation-reduction and osmotic adjustment ability of MS30 were significantly stronger than MS37, the damage degree of the photosynthetic system and membrane system of MS30 is significantly lower than that of MS37. On this basis, the global proteomics analysis was undertaken by tandem mass tags (TMT) technique, a total of 6,704 proteins were identified and quantified. Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that a series of key pathways including photosynthesis, metabolism, adjustment and repair were affected by HT stress. Through analyzing Venn diagrams of two alfalfa varieties, 160 and 213 differentially expressed proteins (DEPs) that had dynamic changes under HT stress were identified from MS30 and MS37, respectively. Among these DEPs, we screened out some key DEPs, such as ATP-dependent zinc metalloprotease FTSH protein, vitamin K epoxide reductase family protein, ClpB3, etc., which plays important functions in response to HT stress. In conclusion, the stronger heat-tolerance of MS30 was attributed to its higher adjustment and repair ability, which could cause the metabolic process of MS30 is more conducive to maintaining its survival and growth than MS37, especially at the later period of HT stress. This study provides a useful catalog of the Medicago sativa L. proteomes with the insight into its future genetic improvement of heat-resistance.

The regulatory activities of microRNAs in non-vascular plants: a mini review

MicroRNA-mediated gene regulation in non-vascular plants is potentially involved in several unique biological functions, including biosynthesis of several highly valuable exclusive bioactive compounds, and those small RNAs could be manipulated for the overproduction of essential bioactive compounds in the future. MicroRNAs (miRNAs) are a class of endogenous, small (20-24 nucleotides), non-coding RNA molecules that regulate gene expression through the miRNA-mediated mechanisms of either translational inhibition or messenger RNA (mRNA) cleavage. In the past years, studies have mainly focused on elucidating the roles of miRNAs in vascular plants as compared to non-vascular plants. However, non-vascular plant miRNAs have been predicted to be involved in a wide variety of specific biological mechanisms; nevertheless, some of them have been demonstrated explicitly, thus showing that the research field of this plant group owns a noteworthy potential to develop novel investigations oriented towards the functional characterization of these miRNAs. Furthermore, the insights into the roles of miRNAs in non-vascular plants might be of great importance for designing the miRNA-based genetically modified plants for valuable secondary metabolites, active compounds, and biofuels in the future. Therefore, in this current review, we provide an overview of the potential roles of miRNAs in different groups of non-vascular plants such as algae and bryophytes.

Effects of excess ammoniacal nitrogen (NH4+-N) on pigments, photosynthetic rates, chloroplast ultrastructure, proteomics, formation of reactive oxygen species and enzymatic activity in submerged plant Hydrilla verticillata (L.f.) Royle

Although excess ammoniacal-nitrogen (NH₄⁺-N) results in the disturbance of various important biochemical and physiological processes, a detailed study on the effects of NH₄⁺-N stress on the photosynthesis and global changes in protein levels in submerged macrophytes is still lacking. Here, the changes of excess NH₄⁺-N on physiological parameters in Hydrilla verticillata (L.f.) Royle, a submerged macrophyte were investigated, including the contents of photosynthetic pigments, soluble sugars, net photosynthesis and respiration, glutamine synthetase (GS) and glutamate synthase (GOGAT) activities, chloroplast ultrastructure, chloroplast reactive oxygen species (ROS) accumulation and protein levels. Our results showed that the net photosynthetic rate and pigment content reached maximum values when the plants were treated with 1 and 2 mg L^-1 NH₄⁺-N, respectively, and decreased at NH₄⁺-N concentrations at 5, 10, 15 and 20 mg L^-1. This decrease might be caused by ROS accumulation. Compared that in 0.02 mg L^-1 NH₄⁺-N as a control, ROS generation in chloroplasts significantly increased in the presence of more than 2 mg L^-1 NH₄⁺-N. Consistently, the damages caused by over-accumulated ROS were observed in chloroplast ultrastructure, showing a loose thylakoid membranes and swollen grana/stroma lamellae. Furthermore, through proteomic analysis, we identified 91 differentially expressed protein spots. Among them, six proteins involved in photosynthesis decreased in abundance in response to excess NH₄⁺-N. Surprisingly, the abundance of all the identified proteins that were involved in nitrogen assimilation and amino acid metabolism tended to increase under excess NH₄⁺-N compared with the control, suggestive of the imbalanced carbon and nitrogen (C-N) metabolisms. In support, activated GS and GOGAT cycle was observed, evidenced by higher activities of GS and GOGAT enzymes. To our knowledge, this work is the first description that excess NH₄⁺-N results in chloroplast ultrastructural damages and the first proteomic evidence to support that excess NH₄⁺-N can lead to a decline in photosynthesis and imbalance of C-N metabolism in submerged macrophytes.

Inhibition of glucose assimilation in Auxenochlorella protothecoides by light

BACKGROUND

The yield of microalgae biomass is the key to affect the accumulation of fatty acids. A few microalgae can assimilate organic carbon to improve biomass yield. In mixotrophic cultivation, microalgae can use organic carbon source and light energy simultaneously. The preference of the main energy source by microalgae determines the biomass yield. Auxenochlorella protothecoides is an oleaginous mixotrophic microalga that can efficiently assimilate glucose and accumulate a large amount of biomass and fatty acids. The current study focused on the effect of light on the growth and glucose assimilation of A. protothecoides.

RESULTS

In this study, we found that the uptake and metabolism of glucose in A. protothecoides could be inhibited by light, resulting in a reduction of biomass growth and lipid accumulation. We employed comparative proteomics to study the influence of light on the regulation of glucose assimilation in A. protothecoides. Proteomics revealed that proteins involving in gene translation and photosynthesis system were up-regulated in the light, such as ribulose-phosphate 3-epimerase and phosphoribulokinase. Calvin cycle-related proteins were also up-regulated, suggesting that light may inhibit glucose metabolism by enhancing the production of glyceraldehyde-3-phosphate (G3P) in the Calvin cycle. In addition, the redox homeostasis-related proteins such as thioredoxin reductase were up-regulated in the light, indicating that light may regulate glucose uptake by changing the redox balance. Moreover, the increase of NADH levels and redox potential of the medium under illumination might inhibit the activity of the glucose transport system and subsequently reduce glucose uptake.

CONCLUSIONS

A theoretical model of how glucose assimilation in A. protothecoides is negatively influenced by light was proposed, which will facilitate further studies on the complex mechanisms underlying the transition from autotrophy to heterotrophy for improving biomass accumulation.

Diurnal.plant.tools: Comparative Transcriptomic and Co-expression Analyses of Diurnal Gene Expression of the Archaeplastida Kingdom

Almost all organisms coordinate some aspects of their biology through the diurnal cycle. Photosynthetic organisms, and plants especially, have established complex programs that coordinate physiological, metabolic and developmental processes with the changing light. The diurnal regulation of the underlying transcriptional processes is observed when groups of functionally related genes (gene modules) are expressed at a specific time of the day. However, studying the diurnal regulation of these gene modules in the plant kingdom was hampered by the large amount of data required for the analyses. To meet this need, we used gene expression data from 17 diurnal studies spanning the whole Archaeplastida kingdom (Plantae kingdom in the broad sense) to make an online diurnal database. We have equipped the database with tools that allow user-friendly cross-species comparisons of gene expression profiles, entire co-expression networks, co-expressed clusters (involved in specific biological processes), time-specific gene expression and others. We exemplify how these tools can be used by studying three important biological questions: (i) the evolution of cell division, (ii) the diurnal control of gene modules in algae and (iii) the conservation of diurnally controlled modules across species. The database is freely available at http://diurnal.plant.tools.

Primary Metabolism Is Distinctly Modulated by Plant Resistance Inducers in Coffea arabica Leaves Infected by Hemileia vastatrix

Epidemics of coffee leaf rust (CLR) leads to great yield losses and huge depreciation of coffee marketing values, if no control measures are applied. Societal expectations of a more sustainable coffee production are increasingly imposing the replacement of fungicide treatments by alternative solutions. A protection strategy is to take advantage of the plant immune system by eliciting constitutive defenses. Based on such concept, plant resistance inducers (PRIs) have been developed. The Greenforce CuCa formulation, similarly to acibenzolar-S-methyl (ASM), shows promising results in the control of CLR (Hemileia vastatrix) in Coffea arabica cv. Mundo Novo. The molecular mechanisms of PRIs action are poorly understood. In order to contribute to its elucidation a proteomic, physiological (leaf gas-exchange) and biochemical (enzymatic) analyses were performed. Coffee leaves treated with Greenforce CuCa and ASM and inoculation with H. vastatrix were considered. Proteomics revealed that both PRIs lead to metabolic adjustments but, inducing distinct proteins. These proteins were related with photosynthesis, protein metabolism and stress responses. Greenforce CuCa increased photosynthesis and stomatal conductance, while ASM caused a decrease in these parameters. It was further observed that Greenforce CuCa reinforces the redox homeostasis of the leaf, while ASM seems to affect preferentially the secondary metabolism and the stress-related proteins. So, the PRIs prepare the plant to resist CLR but, inducing different defense mechanisms upon pathogen infection. The existence of a link between the primary metabolism and defense responses was evidenced. The identification of components of the plant primary metabolism, essential for plant growth and development that, simultaneously, participate in the plant defense responses can open new perspectives for plant breeding programs.

Proteomic analysis of gametophytic sex expression in the fern Ceratopteris thalictroides

Ceratopteris thalictroides, a model fern, has two kinds of gametophytes with different sex expression: male and hermaphrodite. Hermaphroditic gametophytes have one or several archegonia beneath the growing point and a few antheridia at the base or margin. Male gametophytes show a spoon-like shape with much longer than the width and produce many antheridia at the margin and surface. The results of chlorophyll fluorescence detection showed that the photochemical efficiency of hermaphrodites was higher than that of males. By using two-dimensional electrophoresis and mass spectrometry, the differentially abundant proteins in hermaphroditic and male gametophytes were identified. A total of 1136 ± 55 protein spots were detected in Coomassie-stained gels of proteins from hermaphroditic gametophytes, and 1130 ± 65 spots were detected in gels of proteins from male gametophytes. After annotation, 33 spots representing differentially abundant proteins were identified. Among these, proteins involved in photosynthesis and chaperone proteins were over-represented in hermaphrodites, whereas several proteins involved in metabolism were increased in male gametophytes in order to maintain their development under relatively nutritionally deficient conditions. Furthermore, the differentially abundant cytoskeletal proteins detected in this study, such as centrin and actin, may be involved in the formation of sexual organs and are directly related to sex expression. These differentially abundant proteins are important for maintaining the development of gametophytes of different sexes in C. thalictroides.

Comparative proteomics illustrates the complexity of Fe, Mn and Zn deficiency-responsive mechanisms of potato (Solanum tuberosum L.) plants in vitro

The present study is the first to integrate physiological and proteomic data providing information on Fe, Mn and Zn deficiency-responsive mechanisms of potato plants in vitro. Micronutrient deficiency is an important limiting factor for potato production that causes substantial tuber yield and quality losses. To under the underlying molecular mechanisms of potato in response to Fe, Mn and Zn deficiency, a comparative proteomic approach was applied. Leaf proteome change of in vitro-propagated potato plantlets subjected to a range of Fe-deficiency treatments (20, 10 and 0 μM Na-Fe-EDTA), Mn-deficiency treatments (1 and 0 μM MnCl₂·4H₂O) and Zn-deficiency treatment (0 μM ZnCl₂) using two-dimensional gel electrophoresis was analyzed. Quantitative image analysis showed a total of 146, 55 and 42 protein spots under Fe, Mn and Zn deficiency with their abundance significantly altered (P < 0.05) more than twofold, respectively. By MALDI-TOF/TOF MS analyses, the differentially abundant proteins were found mainly involved in bioenergy and metabolism, photosynthesis, defence, redox homeostasis and protein biosynthesis/degradation under the metal deficiencies. Signaling, transport, cellular structure and transcription-related proteins were also identified. The hierarchical clustering results revealed that these proteins were involved in a dynamic network in response to Fe, Mn and Zn deficiency. All these metal deficiencies caused cellular metabolic remodeling to improve metal acquisition and distribution in potato plants. The reduced photosynthetic efficiency occurred under each metal deficiency, yet Fe-deficient plants showed a more severe damage of photosynthesis. More defence mechanisms were induced by Fe deficiency than Mn and Zn deficiency, and the antioxidant systems showed different responses to each metal deficiency. Reprogramming of protein biosynthesis/degradation and assembly was more strongly required for acclimation to Fe deficiency. The signaling cascades involving auxin and NDPKs might also play roles in micronutrient stress signaling and pinpoint interesting candidates for future studies. Our results first provide an insight into the complex functional and regulatory networks in potato plants under Fe, Mn and Zn deficiency.

Analyses of transgenic fibroblast growth factor 21 mature rice seeds

Although some studies have been conducted on the effects of foreign protein expression on rice, the results vary with foreign gene types and protein expression. This study reveals the effects of fibroblast growth factor 21 (FGF21) expression on mature rice seeds in various aspects. Results revealed that the grain weight of the transgene rice was lower than that of non-transgenic wild-type. The sucrose content and ADP-glucose pyrophosphorylase (AGPase) activity in transgenic FGF21 rice were higher than that in non-transgenic wild-type rice, while changes in the starch content, starch branching enzyme (SBE), sucrose synthase (SuS), superoxide dismutase (SOD) and peroxidase (POD) activity were lower in transgenic FGF21 rice compared to non-transgenic wild-type. The scanning electron microscope results revealed that mature seeds of the transgenic FGF21 rice contained fewer vascular bundles with irregular arrangement compared to the wild-type. The mature seeds of CK and T1 rice lines were collected for proteome analysis, and 167 differentially expressed proteins (DEPs) were found. In addition, the most enriched pathways in both rice lines were determined to be amino sugar and nucleotide sugar metabolism and starch and sucrose metabolism, etc. This study laid the foundation for revealing the effects of exogenous protein expression on rice bioreactors.

Bioherbicides: Current knowledge on weed control mechanism

Weed control is a challenging event during crop cultivation. Integrated management, including the application of bioherbicides, is an emerging method for weed control in sustainable agriculture. Plant extracts, allelochemicals and some microbes are utilized as bioherbicides to control weed populations. Bioherbicides based on plants and microbes inhibit the germination and growth of weeds; however,few studies conducted in weed physiology. This review ascribes the current knowledge of the physiological changes in weeds that occur during the exposure to bioherbicides. Plant extracts or metabolites are absorbed by weed seeds, which initiates damage to the cell membrane, DNA, mitosis, amylase activity and other biochemical processes and delays or inhibits seed germination. The growth of weeds is also retarded due to low rates of root-cell division, nutrient uptake, photosynthetic pigment synthesis, and plant growth hormone synthesis, while the productions of reactive oxygen species (ROS) and stress-mediated hormones increase, including irregular antioxidant activity. However, lytic enzymes and toxic substances secreted from microbes degrade the weed seed coat and utilize the endosperm for survival, which inhibits seed germination. The microbes grow through the intercellular spaces to reach the root core, and the deposition of toxins in the cells affects cell division and cellular functions. Some of the metabolites of deleterious microbes cause disease, necrosis and chlorosis,which inhibit the germination and growth of weed seeds by suppressing photosynthesis and gibberellin activities and enhancing ROS, abscisic acid and ethylene. This review explains the effects of bioherbicides (derived from plants and microbes) on weed-plant physiology to elucidate their modes of action.

Acclimation process of cultivating Chlorella vulgaris in toxic excess sludge extract and its response mechanism

Chlorella vulgaris was cultivated in the gradually increased proportion of toxic sludge extracts for acclimation, which was obtained from SBR treated synthetic wastewater containing mixed chlorophenols (2,4,6-trichlorophenol and 4-chlorophenol). The growth of C. vulgaris was obviously improved after acclimation with the cell number in the 100% sludge group was 22.75±0.85∗10⁶cellmL^-1, which was relatively more than the BG11 control group's (20.80±0.35∗10⁶cellmL^-1) and apparently over the 100% sludge group (10.78±0.45∗10⁶cellmL^-1). Compared with the sludge control sludge group, C. vulgaris in the acclimation group gained 24.1% and 18.2% more relative removal rate about TOC and ecotoxicity, respectively. Proteomics analysis showed that protein spots were more clear and centralized and the clarifications of the different protein spots narrowed from 8 to 5 after acclimation. Proteins related to oxidoreducase activity and energy metabolism were over expressed and C. vulgaris could select the metabolic pathways, especially enhanced pyruvate fermentation, TCA cycle, and glycolysis after acclimation, by over accumulating the corresponding vital enzymes. Conclusively, acclimation was a good method to improve the removal ability and growth of C. vulgaris and algae could acclimatize itself to grow upon the toxic sludge extracts by metabolic selection. We suppose acclimation process was a potential method for algae wastewater treatment and algae cultivation without or reduce dilution.

Proteomic analysis of heat stress resistance of cucumber leaves when grafted onto Momordica rootstock

Various biotic and abiotic stresses threaten the cultivation of future agricultural crops. Among these stresses, heat stress is a major abiotic stress that substantially reduces agricultural productivity. Many strategies to enhance heat stress tolerance of crops have been developed, among which is grafting. Here, we show that Momordica-grafted cucumber scions have intrinsically enhanced chlorophyll content, leaf area, and net photosynthetic rate under heat stress compared to plants grafted onto cucumber rootstock. To investigate the mechanisms by which Momordica rootstock enhanced cucumber scions heat stress tolerance, comparative proteomic analysis of cucumber leaves in response to rootstock-grafting and/or heat stress was conducted. Seventy-seven differentially accumulated proteins involved in diverse biological processes were identified by two-dimensional electrophoresis (2-DE) in conjunction with matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry (MALDI-TOF/TOF MS). The following four main categories of proteins were involved: photosynthesis (42.8%), energy and metabolism (18.2%), defense response (14.3%), and protein and nucleic acid biosynthesis (11.7%). Proteomic analysis revealed that scions grafted onto Momordica rootstocks upregulated more proteins involved in photosynthesis compared to scions grafted onto cucumber rootstocks under heat stress and indicated enhanced photosynthetic capacity when seedlings were exposed to heat stress. Furthermore, the expression of photosynthesis-related genes in plants grafted onto Momordica rootstocks significantly increased in response to heat stress. In addition, increased high-temperature tolerance of plants grafted onto Momordica rootstock was associated with the accumulation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and oxygen-evolving enhancer protein 1 (OEE1). Taken together, the data indicated that Momordica rootstock might alleviate growth inhibition caused by heat stress by improving photosynthesis, providing valuable insight into enhancing heat stress tolerance in the global warming epoch.

Insights into the molecular mechanism of the responses for Cyperus alternifolius to PhACs stress in constructed wetlands

Cyperus alternifolius has been widely reported to be an effective phytoremediation plant in constructed wetland systems (CWs). In this context, an integrated biochemical and proteomic analysis of C. alternifolius leaves exposed to pharmaceutically active compounds (PhACs) in CWs was conducted to understand the mechanism of phytoremediation. The obtained results showed the antioxidant enzyme activities were induced throughout the experiment; however over time, the malondialdehyde content is not significantly different from the control and the photosynthetic pigment contents in plant were subsequently slowly recovered. Therefore, we concluded that reactive oxygen species could be effectively counteracted by the enhanced antioxidant enzyme activities, and therefore the photosynthetic pigments were ultimately restored. Leaf extract proteome maps were obtained through 2-DE, and an average of 55, 49, and 24 spots were significantly altered by 30, 100, and 500 μg/L of PhACs over the control, respectively. Protein expression patterns showed that proteins in C. alternifolius leaves are associated with photosynthesis, energy metabolism, defense, and protein synthesis. Moreover, the most relevant pathways modulated by PhACs were photosynthesis and energy metabolism. The protein expression involved in antioxidant defense and stress response generally increased in all the PhAC treatments. The regulated proteins may favor PhAC degradation in CWs; however, the role of these proteins in degrading PhACs remains unknown; further biochemical studies should be conducted. This study indicated that C. alternifolius can tolerate multiple PhACs.

Comparative proteomics illustrates the complexity of drought resistance mechanisms in two wheat (Triticum aestivum L.) cultivars under dehydration and rehydration

BACKGROUND

Drought stress is one of the most adverse environmental constraints to plant growth and productivity. Comparative proteomics of drought-tolerant and sensitive wheat genotypes is a strategy to understand the complexity of molecular mechanism of wheat in response to drought. This study attempted to extend findings regarding the potential proteomic dynamics in wheat under drought stress and to enrich the research content of drought tolerance mechanism.

RESULTS

A comparative proteomics approach was applied to analyze proteome change of Xihan No. 2 (a drought-tolerant cultivar) and Longchun 23 (a drought-sensitive cultivar) subjected to a range of dehydration treatments (18 h, 24 h and 48 h) and rehydration treatment (R24 h) using 2-DE, respectively. Quantitative image analysis showed a total of 172 protein spots in Xihan No. 2 and 215 spots from Longchun 23 with their abundance significantly altered (p < 0.05) more than 2.5-fold. Out of these spots, a total of 84 and 64 differentially abundant proteins were identified by MALDI-TOF/TOF MS in Xihan No. 2 and Longchun 23, respectively. Most of these identified proteins were involved in metabolism, photosynthesis, defence and protein translation/processing/degradation in both two cultivars. In addition, the proteins involved in redox homeostasis, energy, transcription, cellular structure, signalling and transport were also identified. Furthermore, the comparative analysis of drought-responsive proteome allowed for the general elucidation of the major mechanisms associated with differential responses to drought of both two cultivars. These cellular processes work more cooperatively to re-establish homeostasis in Xihan No. 2 than Longchun 23. The resistance mechanisms of Xihan No. 2 mainly included changes in the metabolism of carbohydrates and amino acids as well as in the activation of more antioxidation and defense systems and in the levels of proteins involved in ATP synthesis and protein degradation/refolding.

CONCLUSIONS

This study revealed that the levels of a number of proteins involved in various cellular processes were affected by drought stress in two wheat cultivars with different drought tolerance. The results showed that there exist specific responses to drought in Xihan No. 2 and Longchun 23. The proposed hypothetical model would explain the interaction of these identified proteins that are associated with drought-responses in two cultivars, and help in developing strategies to improve drought tolerance in wheat.

Gel-free/label-free proteomic analysis of wheat shoot in stress tolerant varieties under iron nanoparticles exposure

Iron nanoparticles (Fe NPs) have stimulatory effects on the germination ratio and plant growth of wheat. To elucidate the effects of Fe NPs on shoot of drought tolerant Pakistan-13 and salt tolerant NARC-11, a gel-free/label-free proteomic technique was used. The weights/lengths of seedling, shoot, and root of wheat varieties were increased on 5ppm Fe NPs exposure. The number of proteins related to photosynthesis and protein metabolism was decreased and increased in drought tolerant variety and salt tolerant variety, respectively, treated with Fe NPs compared to untreated plants. Differentially changed proteins in drought tolerant variety and salt tolerant variety were mainly related to photosynthesis. Out of photosynthesis related proteins, light reaction was enhanced in salt tolerant variety compared to drought tolerant variety on Fe NPs exposure. The abundance of ribulose bisphosphate carboxylase/oxygenase small chain in drought tolerant variety was higher than that in salt tolerant variety; however, in salt tolerant variety, it was increased 3 fold by Fe NPs exposure compared to untreated plant. These results suggest that Fe NPs improve the growth of wheat seedling, which might be associated with the increase of protein abundance in photosynthesis in salt tolerant variety.

Phytotoxic mechanisms of bur cucumber seed extracts on lettuce with special reference to analysis of chloroplast proteins, phytohormones, and nutritional elements

Bioherbicides from plant extracts are an effective and environmentally friendly method to prevent weed growth. The present investigation was aimed at determining the inhibitory effect of bur cucumber seed extracts (BSE) on lettuce plant growth. Bur cucumber seeds were ground with water, and two different concentrations of seed extracts (10% and 20%) were prepared and applied to lettuce plants. Decreased plant height, number of leaves, leaf length, leaf width, anProd. Type: FTPd leaf area were found in lettuce exposed to BSE as compared with controls. A significant reduction in lettuce biomass was observed in 20% BSE-treated plants due to the presence of higher amounts of phenolic content in the extracts. Moreover, a significant inhibitory chemical, 2-linoleoyl glycerol, was identified in BSE extracts. The mechanism of plant growth inhibition was assayed in lettuce proteins by 2-dimensional electrophoresis (2-DE) and the LC-MS/MS method. In total, 57 protein spots were detected in plants treated with 20% BSE and control plants. Among these, 39 proteins were down-regulated and 18 proteins were up-regulated in plants exposed to 20% BSE as compared with controls. The presence of low levels of chlorophyll a/b binding protein and oxygen-evolving enhancer protein 1 in BSE-exposed plants reduced photosynthetic pigment synthesis and might be a reason for stunted plant growth. Indeed, the plant-growth stimulating hormone gibberellin was inhibited, and synthesis of stress hormones such as abscisic acid, jasmonic acid, and salicylic acid were triggered in lettuce by the effects of BSE. Uptake of essential nutrients, Ca, Fe, Mg, K, S, and Mo, was deficient and accumulation of the toxic ions Cu, Zn, and Na was higher in BSE-treated plants. The results of this study suggest that extracts of bur cucumber seeds can be an effective eco-friendly bioherbicide for weed control that work by inhibiting mechanisms of photosynthesis and regulating phytohormones and nutritional elements.

Proteomic Analysis of the Relationship between Metabolism and Nonhost Resistance in Soybean Exposed to Bipolaris maydis

Nonhost resistance (NHR) pertains to the most common form of plant resistance against pathogenic microorganisms of other species. Bipolaris maydis is a non-adapted pathogen affecting soybeans, particularly of maize/soybean intercropping systems. However, no experimental evidence has described the immune response of soybeans against B. maydis. To elucidate the molecular mechanism underlying NHR in soybeans, proteomics analysis based on two-dimensional polyacrylamide gel electrophoresis (2-DE) was performed to identify proteins involved in the soybean response to B. maydis. The spread of B. maydis spores across soybean leaves induced NHR throughout the plant, which mobilized almost all organelles and various metabolic processes in response to B. maydis. Some enzymes, including ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), mitochondrial processing peptidase (MPP), oxygen evolving enhancer (OEE), and nucleoside diphosphate kinase (NDKs), were found to be related to NHR in soybeans. These enzymes have been identified in previous studies, and STRING analysis showed that most of the protein functions related to major metabolic processes were induced as a response to B. maydis, which suggested an array of complex interactions between soybeans and B. maydis. These findings suggest a systematic NHR against non-adapted pathogens in soybeans. This response was characterized by an overlap between metabolic processes and response to stimulus. Several metabolic processes provide the soybean with innate immunity to the non-adapted pathogen, B. maydis. This research investigation on NHR in soybeans may foster a better understanding of plant innate immunity, as well as the interactions between plant and non-adapted pathogens in intercropping systems.

Antioxidant Activity of Oxygen Evolving Enhancer Protein 1 Purified from Capsosiphon fulvescens

This study was conducted to determine the antioxidant activity of a protein purified from Capsosiphon fulvescens. The purification steps included sodium acetate (pH 6) extraction and diethylaminoethyl-cellulose, reversed phase Shodex C4P-50 column chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis indicated that the molecular weight of the purified protein was 33 kDa. The N-terminus and partial peptide amino acid sequence of this protein was identical to the sequence of oxygen evolving enhancer (OEE) 1 protein. The antioxidant activity of the OEE 1 was determined in vitro using a scavenging test with 4 types of reactive oxygen species (ROS), including the 2,2-diphenyl-1-picrylhydrazyl radical, hydroxyl radical, superoxide anion, and hydrogen peroxide (H2 O2 ). OEE 1 had higher H2 O2 scavenging activity, which proved to be the result of enzymatic antioxidants rather than nonenzymatic antioxidants. In addition, OEE 1 showed less H2 O2 -mediated ROS formation in HepG2 cells. In conclusion, this study demonstrates that OEE 1 purified from C. fulvescens is an excellent antioxidant.

Zn deficiency in Brassica napus induces Mo and Mn accumulation associated with chloroplast proteins variation without Zn remobilization

The importance of zinc (Zn) has been of little concern in human nutrition despite a strong decrease of this element in crops since the rise of high yielding varieties. For better food quality, Zn biofortification can be used, but will be optimal only if mechanisms governing Zn management are better known. Using Zn deficiency, we are able to demonstrate that Zn is not remobilized in Brassica napus (B. napus). Thus, remobilization processes should not be targeted by biofortification strategies. This study also complemented previous work by investigating leaf responses to Zn deficiency, especially from proteomic and ionomic points of view, showing for example, an increase in Manganese (Mn) content and of the Mn-dependent protein, Oxygen Evolving Enhancer.

Photosynthetic and molecular responses of the marine diatom Thalassiosira pseudonana to triphenyltin exposure

This study aimed to investigate the responses of the marine diatom Thalassiosira pseudonana upon waterborne exposure to triphenyltin chloride (TPTCl) through determining their photosynthetic response, growth performance, and expressions of genes and proteins. Based on the growth inhibition test, the 96-h IC50 (i.e., median inhibition concentration) was found to be 1.09 μg/L (95% confidence interval (CI): 0.89-1.34 μg/L). According to photosynthetic parameters, the 96-h EC50s (i.e., median effect concentrations) were estimated at 1.54 μg/L (95% CI: 1.40-1.69 μg/L) and 1.51 μg/L (95% CI: 1.44-1.58 μg/L) for the maximum quantum yield of photosystem II (PSII) photochemistry (ΦPo) and the effective quantum yield of photochemical energy conversion in PSII (Φ2), respectively. Non-photochemical quenching in the algae was increased at low concentrations of TPTCl (0.5-1.0 μg/L) but it decreased gradually when the TPTCl concentration further increased from 1.0 to 2.5 μg/L. Results of gene expressions showed that lipid metabolism related genes were not influenced by TPTCl at 0.5 or 1.0 μg/L, while silica shell formation genes were down-regulated at 0.5 μg/L. Photosynthesis related genes were up-regulated at 0.5 μg/L TPTCl but were down-regulated at 1.0 μg/L TPTCl. Proteomics analysis revealed that relatively less proteins could be detected after exposure to 1.0 μg/L TPTCl (only about 50-60 spots) compared with that observed in the 0.5μg/L TPTCl treatment and two control groups (each with about 290-300 protein spots). At 0.5 μg/L TPTCl, five proteins were differentially expressed when compared with the seawater control and solvent control, and most of these proteins are involved in defence function to protect the biological systems from reactive oxygen species that generated by TPTCl. These proteins include oxygen-evolving enhancer protein 1 precursor, fucoxanthin chlorophyll a/c protein - LI818 clade, and mitochondrial manganese superoxide dismutase, which can function to maintain the capacity of PSII and stabilize the photosynthesis efficiency as reflected by the unchanged ΦPo and Φ2 values at 0.5 μg/L TPTCl. In contrast, the excess toxicity that caused by TPTCl at the high concentration (1.0 μg/L TPTCl) might directly damage the proteins, inhibit their expression, and/or cause the suppression of metabolism as indicated by the down-regulation of most studied proteins and genes, which could ultimately inhibit the photosynthesis and growth of the algae. Overall, this study comprehensively elucidated the toxicity effects of TPT on T. pseudonana, and partially revealed the molecular toxic mechanisms and corresponding defence responses in this model algal species.

Transcriptomic and proteomic analysis of a compatible tomato-aphid interaction reveals a predominant salicylic acid-dependent plant response

BACKGROUND

Aphids are among the most destructive pests in temperate climates, causing significant damage on several crops including tomato. We carried out a transcriptomic and proteomic study to get insights into the molecular mechanisms and dynamics of the tomato response to the Macrosyphum euphorbiae aphid.

RESULTS

The time course analysis of aphid infestation indicated a complex, dynamic pattern of gene expression. Several biological functions were affected and genes related to the stress and defence response were the most represented. The Gene Ontology categories of the differentially expressed genes (899) and identified proteins (57) indicated that the tomato response is characterized by an increased oxidative stress accompanied by the production of proteins involved in the detoxification of oxygen radicals. Aphids elicit a defense reaction based on the cross-communication of different hormone-related signaling pathways such as those related to the salicylic acid (SA), jasmonic acid (JA), ethylene and brassinosteroids. Among them, the SA-signaling pathway and stress-responsive SA-dependent genes play a dominant role. Furthermore, tomato response is characterized by a reduced accumulation of photosynthetic proteins and a modification of the expression of various cell wall related genes.

CONCLUSIONS

Our work allowed a more comprehensive understanding of the signaling events and the defense dynamics of the tomato response to aphids in a compatible interaction and, based on experimental data, a model of the tomato-aphid molecular interaction was proposed. Considering the rapid advancement of tomato genomics, this information will be important for the development of new protection strategies.

Proteomic analysis of grape berry skin responding to sunlight exclusion

The most obvious effect of sunlight exclusion from grape clusters is the inhibition of anthocyanin biosynthesis in the berry skin so that no color develops. Two-dimensional gel electrophoresis coupled with mass spectrometry was used to characterize the proteins isolated from berry skins that developed under sunlight exclusion versus those from sunlight-exposed berries. Among more than 1500 spots resolved in stained gels, the accumulation patterns of 96 spots differed significantly between sunlight-excluded berry skin and that of sunlight-exposed control berries. Seventy-two proteins, including 35 down-regulated and 37 up-regulated proteins, were identified and categorized. Proteins involved in photosynthesis and secondary metabolism, especially UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT), the key step for anthocyanin biosynthesis in grape berry skin, were accumulated less in the absence of sunlight. Several isoforms of heat shock proteins were also down-regulated. The proteins that were over-accumulated in sunlight-excluded berry skin were more often related to energy production, glycolysis, the tricarboxylic-acid cycle, protein synthesis and biogenesis of cellular components. Their putative role is discussed in terms of their relevance to sunlight exclusion processes.

Proteins linked to drought tolerance revealed by DIGE analysis of drought resistant and susceptible barley varieties

Drought is a major threat to world agriculture. In order to identify proteins associated with plant drought tolerance, barley varieties bred in the UK (Golden Promise) and Iraq (Basrah) were compared. The variety Basrah showed physiological adaptations to drought when compared to Golden Promise, for example relative water content of roots and shoots after 1 week of drought was much higher for Basrah than for Golden Promise. DIGE analysis was carried out on proteins from roots and leaves under control and drought conditions. Twenty-four leaf and 45 root proteins were identified by MALDI-TOF MS. The relative expression patterns of the identified proteins fell into a number of distinct classes. The variety Basrah is characterised by constitutive expression or higher drought-induced expression levels of proteins regulating ROS production and protein folding. Photosynthetic enzymes, by contrast, were downregulated in Basrah. Enzyme assays showed a good correlation between DIGE-derived protein abundance estimates and enzyme activity in extracts. Overall, this study shows that the enhanced drought tolerance of variety Basrah is driven by an enhanced regulation of ROS under drought.

Comparative analysis of cells and proteins of pumpkin plants for the control of fruit size

Common pumpkin plants (Cucurbita maxima) produce fruits of 1-2 kg size on the average, while special varieties of the same species called Atlantic Giant are known to produce a huge fruit up to several hundred kilograms. As an approach to determine the factors controlling the fruit size in C. maxima, we cultivated both AG and control common plants, and found that both the cell number and cell sizes were increased in a large fruit while DNA content of the cell did not change significantly. We also compared protein patterns in the leaves, stems, ripe and young fruits by two-dimensional (2D) gel electrophoresis, and identified those differentially expressed between them with mass spectroscopy. Based on these results, we suggest that factors in photosynthesis such as ribulose-bisphosphate carboxylase, glycolysis pathway enzymes, heat-shock proteins and ATP synthase play positive or negative roles in the growth of a pumpkin fruit. These results provide a step toward the development of plant biotechnology to control fruit size in the future.

Cellular oxido-reductive proteins of Chlamydomonas reinhardtii control the biosynthesis of silver nanoparticles

Background

Elucidation of molecular mechanism of silver nanoparticles (SNPs) biosynthesis is important to control its size, shape and monodispersity. The evaluation of molecular mechanism of biosynthesis of SNPs is of prime importance for the commercialization and methodology development for controlling the shape and size (uniform distribution) of SNPs. The unicellular algae Chlamydomonas reinhardtii was exploited as a model system to elucidate the role of cellular proteins in SNPs biosynthesis.

Results

The C. reinhardtii cell free extract (in vitro) and in vivo cells mediated synthesis of silver nanoparticles reveals SNPs of size range 5 ± 1 to 15 ± 2 nm and 5 ± 1 to 35 ± 5 nm respectively. In vivo biosynthesized SNPs were localized in the peripheral cytoplasm and at one side of flagella root, the site of pathway of ATP transport and its synthesis related enzymes. This provides an evidence for the involvement of oxidoreductive proteins in biosynthesis and stabilization of SNPs. Alteration in size distribution and decrease of synthesis rate of SNPs in protein-depleted fractions confirmed the involvement of cellular proteins in SNPs biosynthesis. Spectroscopic and SDS-PAGE analysis indicate the association of various proteins on C. reinhardtii mediated in vivo and in vitro biosynthesized SNPs. We have identified various cellular proteins associated with biosynthesized (in vivo and in vitro) SNPs by using MALDI-MS-MS, like ATP synthase, superoxide dismutase, carbonic anhydrase, ferredoxin-NADP⁺ reductase, histone etc. However, these proteins were not associated on the incubation of pre-synthesized silver nanoparticles in vitro.

Conclusion

Present study provides the indication of involvement of molecular machinery and various cellular proteins in the biosynthesis of silver nanoparticles. In this report, the study is mainly focused towards understanding the role of diverse cellular protein in the synthesis and capping of silver nanoparticles using C. reinhardtii as a model system.

Expressed sequence tag (EST) profiling in hyper saline shocked Dunaliella salina reveals high expression of protein synthetic apparatus components

The unicellular, halotolerant, green alga, Dunaliella salina (Chlorophyceae) has the unique ability to adapt and grow in a wide range of salt conditions from about 0.05 to 5.5M. To better understand the molecular basis of its salinity tolerance, a complementary DNA (cDNA) library was constructed from D. salina cells adapted to 2.5M NaCl, salt-shocked at 3.4M NaCl for 5h, and used to generate an expressed sequence tag (EST) database. ESTs were obtained for 2831 clones representing 1401 unique transcripts. Putative functions were assigned to 1901 (67.2%) ESTs after comparison with protein databases. An additional 154 (5.4%) ESTs had significant similarity to known sequences whose functions are unclear and 776 (27.4%) had no similarity to known sequences. For those D. salina ESTs for which functional assignments could be made, the largest functional categories included protein synthesis (35.7%), energy (photosynthesis) (21.4%), primary metabolism (13.8%) and protein fate (6.8%). Within the protein synthesis category, the vast majority of ESTs (80.3%) encoded ribosomal proteins representing about 95% of the approximately 82 subunits of the cytosolic ribosome indicating that D. salina invests substantial resources in the production and maintenance of protein synthesis. The increased mRNA expression upon salinity shock was verified for a small set of selected genes by real-time, quantitative reverse-transcription-polymerase chain reaction (qRT-PCR). This EST collection also provided important new insights into the genetic underpinnings for the biosynthesis and utilization of glycerol and other osmoprotectants, the carotenoid biosynthetic pathway, reactive oxygen-scavenging enzymes, and molecular chaperones (heat shock proteins) not described previously for D. salina. EST discovery also revealed the existence of RNA interference and signaling pathways associated with osmotic stress adaptation. The unknown ESTs described here provide a rich resource for the identification of novel genes associated with the mechanistic basis of salinity stress tolerance and other stress-adaptive traits.

Genome-wide analysis of thiourea-modulated salinity stress-responsive transcripts in seeds of Brassica juncea: identification of signalling and effector components of stress tolerance

BACKGROUND AND AIMS

Abiotic stresses including salinity are the major constraints to crop production. In this regard, the use of thiourea (TU) in imparting salinity-stress tolerance to Indian mustard (Brassica juncea) has been demonstrated earlier. To gain an insight into the mechanism of TU action, various molecular and biochemical studies were conducted.

METHODS

Microarray analysis was performed in seeds subjected to distilled water (control), 1 m NaCl, 1 m NaCl + 6·5 mm TU and 6·5 mm TU alone for 1 h. Real-time PCR validation of selected genes and biochemical studies were conducted under similar treatments at 1 h and 6 h.

KEY RESULTS

The microarray analysis revealed a differential expression profile of 33 genes in NaCl- and NaCl + TU-treated seeds, most of which are established markers of stress tolerance. The temporal regulation of eight selected genes by real-time PCR indicated their early and co-ordinated induction at 1 h in NaCl + TU only. Besides, NaCl + TU-treated seeds also maintained a higher level of abscisic acid, reduced to oxidized glutathione (GSH : GSSG) ratio and activities of catalase, phenylalanine ammonia lyase and glutathione-S-transferases, as compared with that of NaCl treatment. The addition of LaCl(3) (a specific calcium-channel blocker) restricted the responses of TU both at molecular and biochemical level suggesting the possible involvement of a cytosolic calcium burst in the TU-mediated response. The TU-alone treatment was comparable to that of the control; however, it reduced the expression of some transcription factors and heat-shock proteins presumably due to the stabilization of the corresponding proteins.

CONCLUSIONS

The TU treatment co-ordinately regulates different signalling and effector mechanisms at an early stage to alleviate stress even under a high degree of salinity. This also indicates the potential of TU to be used as an effective bioregulator to impart salinity tolerance under field conditions.

Detection of an L-amino acid dehydrogenase activity in Synechocystis sp. PCC 6803

The protein Slr0782 from Synechocystis sp. PCC 6803, which has similarity to L-amino acid oxidase from Synechococcus elongatus PCC 6301 and PCC 7942, has been characterized in part. Immunoblot blot analysis showed that Slr0782 is mainly thylakoid membrane-associated. Moreover, expression of slr0782 mRNA and Slr0782 protein were analyzed and an activity assay was developed. Utilizing toluene-permeabilized cells, an L-arginine-stimulated O(2) uptake became detectable in Synechocystis sp. PCC 6803. Besides oxidizing the basic L-amino acids L-arginine, L-lysine, L-ornithine, and L-histidine, a number of other L-amino acids were also substrates, while D-amino acids were not. The best substrate was L-cysteine, and the second best was L-arginine. The L-arginine-stimulated O(2) uptake was inhibited by cations. The inhibition by o-phenanthroline and salicylhydroxamic acid suggested the presence of a transition metal besides FAD in the enzyme. Moreover, it is shown that inhibitors of the respiratory electron transport chain, such as KCN and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, also inhibited the L-arginine-stimulated O(2) uptake, suggesting that Slr0782 functions as an L-arginine dehydrogenase, mediating electron transfer from L-arginine into the respiratory electron transport chain utilizing O(2) as electron acceptor via cytochrome oxidase. The results imply that Slr0782 is an additional substrate dehydrogenase being able to interact with the electron transport chain of the thylakoid membrane.

Morphological and molecular characterization of a spontaneously tuberizing potato mutant: an insight into the regulatory mechanisms of tuber induction

BACKGROUND

Tuberization in potato (Solanum tuberosum L.) represents a morphogenetic transition of stolon growth to tuber formation, which is under complex environmental and endogenous regulation. In the present work, we studied the regulatory mechanisms and the role of different morphogenetic factors in a newly isolated potato mutant, which exhibited spontaneous tuberization (ST). The ST mutant was characterized in detail at morphological, physiological and biochemical levels.

RESULTS

Tuberization of the ST mutant grown in the soil was photoperiod-insensitive; predominantly sessile tubers formed directly from axillary buds even under continuous light. Single-node cuttings of the ST mutant cultured in vitro frequently formed tubers or basal tuber-like swellings instead of normal shoots under conditions routinely used for shoot propagation. The tuberization response of ST cuttings under light was dependent on sucrose, the concentration of which had to exceed certain threshold that inversely correlated with irradiance. Gibberellic acid prevented tuberization of ST cuttings, but failed to restore normal shoot phenotype and caused severe malformations. Carbohydrate analysis showed increased levels of both soluble sugars and starch in ST plants, with altered carbohydrate partitioning and metabolism. Comparative proteomic analysis revealed only a few differences between ST- and wild-type plants, primary amongst which seemed to be the absence of an isoform of manganese-stabilizing protein, a key subunit of photosystem II.

CONCLUSION

ST mutant exhibits complex developmental and phenotypic modifications, with features that are typical for plants strongly induced to tuberize. These changes are likely to be related to altered regulation of photosynthesis and carbohydrate metabolism rather than impaired transduction of inhibitory gibberellin or photoperiod-based signals. The effect of gibberellins on tuberization of ST mutant suggests that gibberellins inhibit tuberization downstream of the inductive effects of sucrose and other positive factors.

Transcript profiling indicates that the absence of PsbO affects the coordination of C and N metabolism in Synechocystis sp. PCC 6803

Transcript profiling of nitrate-grown Synechocystis sp. PCC 6803 PsbO-free mutant cells in comparison to wild-type (WT) detected substantial deviations. Because we had previously observed phenotypical differences between Synechocystis sp. PCC 6803 WT and its corresponding PsbO-free mutant when cultivated with l-arginine as sole N source and a light intensity of 200 mumol photons m(-2) s(-1), we also performed transcript profiling for both strains grown either with nitrate or with l-arginine as sole N source. We observed a total number of 520 differentially regulated transcripts in Synechocystis WT because of a shift from nitrate- to l-arginine-containing BG11 medium, while we detected only 13 differentially regulated transcripts for the PsbO-free mutant. Thus, the PsbO-free Synechocystis mutant had already undergone a preconditioning process for growth with l-arginine in comparison to WT. While Synechocystis WT suffered from growth with l-arginine at a light intensity of 200 mumol photons m(-2) s(-1), the PsbO-free mutant developed only a minor stress phenotype. In summary, our results suggest that the absence of PsbO in Synechocystis affects the coordination of photosynthesis/respiration and l-arginine metabolism through complex probably redox-mediated regulatory pathways. In addition, we show that a comparison of the transcriptomes of nitrate-grown Synechococcus elongatus PCC 7942 WT cells and its corresponding PsbO-free mutant cells resulted in only a few differentially regulated transcripts between both strains. The absence of the manganese/calcium-stabilizing PsbO protein of PSII with an assigned regulatory function for photosynthetic water oxidation causes bigger changes in the transcriptome of the permissive photoheterotrophically growing Synechocystis sp. PCC 6803 than in the transcriptome of the obligate photoautotrophically growing S. elongatus PCC 7942.

Thioredoxin target proteins in chloroplast thylakoid membranes

In recent years, impressive progress has been made in the identification of thioredoxin-linked proteins. However, due to technical difficulties inherent in working with hydrophobic proteins, identifications so far have been restricted to proteins in the soluble fraction. Thus, our knowledge of redox regulated membrane proteins is quite limited. To gain information in this area, the authors have applied an adaptation of the approach based on the fluorescent thiol probe monobromobimane (mBBr) to identify redox-linked proteins of chloroplast thylakoids. By application of this procedure, 14 potential membrane-bound thioredoxin target proteins were identified, including seven new candidates functional in processes associated with photosynthetic electron flow, ATP synthesis, and Photosystem II/Photosystem I state transitions.

Constitutive expression of the pea ABA-responsive 17 (ABR17) cDNA confers multiple stress tolerance in Arabidopsis thaliana

The constitutive expression of the pea ABR17 (abscisic acid-responsive 17) cDNA, which is a member of the group 10 family of pathogenesis-related proteins (PR 10), in Arabidopsis thaliana is reported. The presence of ABR17 transcripts and the protein in the three transgenic lines is demonstrated by reverse transcriptase-polymerase chain reaction (RT-PCR) and two-dimensional electrophoresis followed by tandem mass spectrometry, respectively. Three independently derived transgenic lines containing ABR17 germinated better in the presence of salt, cold temperature or both. Furthermore, the transgenic plants also exhibited enhanced tolerance to freezing temperature, suggesting the potential utility of the ABR17 gene to engineer multiple stress tolerance. In order to obtain insights into the mechanism underlying ABR17-mediated stress tolerance, we have compared the proteome of a transgenic line with that of its wild-type counterpart. Several proteins were observed to be significantly altered in the transgenic line, including some with a role(s) in photosynthesis, stress tolerance and the regulation of gene expression. Our findings are discussed within the context of available genes to engineer multiple stress tolerance as well as the biological activities of the ABR17 protein.

Comparative proteomics of high light stress in the model algaChlamydomonas reinhardtii

High light (HL) stress adversely affects growth, productivity and viability of photosynthetic organisms. The green alga Chlamydomonas reinhardtii is a model system to study photosynthesis and light stress. Comparative proteomics of wild-type and two very high light (VHL)-resistant mutants, VHL(R)-S4 and VHL(R)-S9, revealed complex alterations in response to excess light. A two-dimensional reference map of the soluble subproteome was constructed representing about 1500 proteins. A total of 83 proteins from various metabolic pathways were identified by peptide mass fingerprinting. Quantitative comparisons of 444 proteins showed 105 significantly changed proteins between wild type and mutants under different light conditions. Commonly, more proteins were decreased than increased, but different proteins were affected in each genotype. Proteins uniquely altered in either VHL(R) mutant may be involved in VHL resistance. Such candidate proteins similarly altered without light stress, thus possibly contributing to "pre-adaptation" of mutants to VHL, included decreased levels of a DEAD box RNA helicase (VHL(R)-S4) and NAB1 and RB38 proteins (VHL(R)-S9), and increased levels of an oxygen evolving enhancer 1 (OEE1) isoform and an unknown protein (VHL(R)-S4). Changes from increased levels in HL to decreased levels in excess light, included OEE1 (VHL(R)-S9) or the reverse change for NAB1, RB38, beta-carbonic anhydrase and an ABC transporter-like protein (VHL(R)-S4).

Identification of plant glutaredoxin targets

Glutaredoxins (Grxs) are small ubiquitous proteins of the thioredoxin (Trx) family, which catalyze dithiol-disulfide exchange reactions or reduce protein-mixed glutathione disulfides. In plants, several Trx-interacting proteins have been isolated from different compartments, whereas very few Grx-interacting proteins are known. We describe here the determination of Grx target proteins using a mutated poplar Grx, various tissular and subcellular plant extracts, and liquid chromatography coupled to tandem mass spectrometry detection. We have identified 94 putative targets, involved in many processes, including oxidative stress response [peroxiredoxins (Prxs), ascorbate peroxidase, catalase], nitrogen, sulfur, and carbon metabolisms (methionine synthase, alanine aminotransferase, phosphoglycerate kinase), translation (elongation factors E and Tu), or protein folding (heat shock protein 70). Some of these proteins were previously found to interact with Trx or to be glutathiolated in other organisms, but others could be more specific partners of Grx. To substantiate further these data, Grx was shown to support catalysis of the stroma beta-type carbonic anhydrase and Prx IIF of Arabidopsis thaliana, but not of poplar 2-Cys Prx. Overall, these data suggest that the interaction could occur randomly either with exposed cysteinyl disulfide bonds formed within or between target proteins or with mixed disulfides between a protein thiol and glutathione.

The MntC crystal structure suggests that import of Mn2+ in cyanobacteria is redox controlled

The MntC protein is the periplasmic solute-binding protein component of the high-affinity manganese ATP-binding cassette-type transport system in the cyanobacterium Synechocytis PCC sp. 6803. We have determined the structure of recombinant MntC at 2.9 A resolution by X-ray crystallography using a combination of multi-wavelength anomalous diffraction and molecular replacement. The presence of Mn2+ in the metal ion-binding site was ascertained by use of anomalous difference electron density maps using diffraction data collected at the Mn absorption edge. The MntC protein is similar to previously determined metal ion-binding, solute-binding proteins with two globular domains connected by an extended alpha-helix. However, the metal ion-binding site is asymmetric, with two of the four ligating residues (Glu220 and Asp295) situated closer to the ion than the two histidine residues (His89 and His154). A unique characteristic of the MntC is the existence of a disulfide bond between Cys219 and Cys268. Analysis of amino acid sequences of homologous proteins shows that conservation of the cysteine residues forming the disulfide bond occurs only in cyanobacterial manganese solute-binding proteins. One of the monomers in the MntC asymmetric unit trimer is disordered significantly in the globular domain containing the disulfide bond. The electron density on the manganese ion and on the disulfide bond in this monomer indicates that reduction of this bond changes the relative position of the lower domain and of the Glu220 ligand, potentially lowering the affinity towards Mn2+. This is confirmed by reduction of the disulfide bond in vitro, showing the release of bound Mn2+. We propose that the reduction or oxidation state of the disulfide bond can alter the binding affinity of the protein towards Mn2+ and thus determine whether these ions will be transported into the cytoplasm, or be available for photosystem II biogenesis in the periplasm.

Redox regulation in the chloroplast thylakoid lumen: a new frontier in photosynthesis research

Initially linked to photosynthesis, regulation by change in the redox state of thiol groups (S-S<-- -->2SH) is now known to occur throughout biology. Thus, in addition to serving important structural and catalytic functions, it is recognized that, in many cases, disulphide bonds can be broken and reformed for regulation. Several systems, each linking a hydrogen donor to an intermediary disulphide protein, act to effect changes that alter the activity of target proteins by change in the thiol redox state. Pertinent to the present discussion is the chloroplast ferredoxin/thioredoxin system, comprised of photoreduced ferredoxin, a thioredoxin, and the enzyme ferredoxin-thioredoxin reductase, that occur in the stroma. In this system, thioredoxin links the activity of enzymes to light: those enzymes functional in biosynthesis are reductively activated by light via thioredoxin (S-S-->2SH), whereas counterparts acting in degradation are deactivated under illumination conditions and are oxidatively activated in the dark (2SH-->S-S). Recent research has uncovered a new paradigm in which an immunophilin, FKBP13, and potentially other enzymes of the chloroplast thylakoid lumen are oxidatively activated in the light (2SH-->S-S). The present review provides a perspective on this recent work.

Structural analysis uncovers a role for redox in regulating FKBP13, an immunophilin of the chloroplast thylakoid lumen

Change in redox status has long been known to link light to the posttranslational regulation of chloroplast enzymes. So far, studies have been conducted primarily with thioredoxin-linked members of the stroma that function in a broad array of biosynthetic and degradatory processes. Consequently, little is known about the role of redox in regulating the growing number of enzymes found to occur in the lumen, the site of oxygen evolution in thylakoid membranes. To help fill this gap, we have studied AtFKBP13, an FKBP-type immunophilin earlier shown to interact with a redox-active protein of the lumen, and found the enzyme to contain a pair of disulfide bonds in x-ray structural studies. These disulfides, which in protein mutagenesis experiments were shown to be essential for the associated peptidyl-prolyl isomerase activity, are unique to chloroplast FKBPs and are absent in animal and yeast counterparts. Both disulfide bonds were redox-active and were reduced by thioredoxin from either chloroplast or bacterial sources in a reaction that led to loss of enzyme activity. The results suggest a previously unrecognized paradigm for redox regulation in chloroplasts in which activation by light is achieved in concert with oxygen evolution by the oxidation of sulfhydryl groups (conversion of SH to S-S). Such a mechanism, occurring in the thylakoid lumen, is in direct contrast to regulation of enzymes in the stroma, where reduction of disulfides targeted by thioredoxin (S-S converted to SH) leads to an increase in activity in the light.

New thioredoxin targets in the unicellular photosynthetic eukaryote Chlamydomonas reinhardtii

Proteomics were used to identify the proteins from the eukaryotic unicellular green alga Chlamydomonas reinhardtii that can be reduced by thioredoxin. These proteins were retained specifically on a thioredoxin affinity column made of a monocysteinic thioredoxin mutant able to form mixed disulfides with its targets. Of a total of 55 identified targets, 29 had been found previously in higher plants or Synechocystis, but 26 were new targets. Biochemical tests were performed on three of them, showing a thioredoxin-dependent activation of isocitrate lyase and isopropylmalate dehydrogenase and a thioredoxin-dependent deactivation of catalase that is redox insensitive in Arabidopsis. In addition, we identified a Ran protein, a previously uncharacterized nuclear target in a photosynthetic organism. The metabolic and evolutionary implications of these findings are discussed.