Overexpression of 2-cysteine peroxiredoxin enhances tolerance to methyl viologen-mediated oxidative stress and high temperature in potato plants

Oxidative stress is one of the major causative factors for injury to plants exposed to environmental stresses. Plants have developed diverse defense mechanisms for scavenging oxidative stress-inducing molecules. The antioxidative enzyme 2-cysteine peroxiredoxin (2-Cys Prx) removes peroxides and protects the photosynthetic membrane from oxidative damage. In this study, transgenic potato (Solanum tuberosum L. cv. Atlantic) expressing At2-Cys Prx under control of the oxidative stress-inducible SWPA2 promoter or enhanced CaMV 35S promoter (referred to as SP and EP plants, respectively) was generated using Agrobacterium-mediated transformation. The transgenic plants were tested for tolerance to stress. Following treatment with 3 μM methyl viologen (MV), leaf discs from SP and EP plants showed approximately 33 and 15% less damage than non-transformed (NT) plants. When 300 μM MV was sprayed onto whole plants, the photosynthetic activity of SP plants decreased by 25%, whereas that of NT plants decreased by 60%. In addition, SP plants showed enhanced tolerance to high temperature at 42 °C. After treatment at high temperature, the photosynthetic activity of SP plants decreased by about 7% compared to plants grown at 25 °C, whereas it declined by 31% in NT plants. These results indicate that transgenic potato can efficiently regulate oxidative stress from various environmental stresses via overexpression of At2-Cys Prx under control of the stress-inducible SWPA2 promoter.     

Heat stress: an overview of molecular responses in photosynthesis

The primary targets of thermal damage in plants are the oxygen evolving complex along with the associated cofactors in photosystem II (PSII), carbon fixation by Rubisco and the ATP generating system. Recent investigations on the combined action of moderate light intensity and heat stress suggest that moderately high temperatures do not cause serious PSII damage but inhibit the repair of PSII. The latter largely involves de novo synthesis of proteins, particularly the D1 protein of the photosynthetic machinery that is damaged due to generation of reactive oxygen species (ROS), resulting in the reduction of carbon fixation and oxygen evolution, as well as disruption of the linear electron flow. The attack of ROS during moderate heat stress principally affects the repair system of PSII, but not directly the PSII reaction center (RC). Heat stress additionally induces cleavage and aggregation of RC proteins; the mechanisms of such processes are as yet unclear. On the other hand, membrane linked sensors seem to trigger the accumulation of compatible solutes like glycinebetaine in the neighborhood of PSII membranes. They also induce the expression of stress proteins that alleviate the ROS-mediated inhibition of repair of the stress damaged photosynthetic machinery and are required for the acclimation process. In this review we summarize the recent progress in the studies of molecular mechanisms involved during moderate heat stress on the photosynthetic machinery, especially in PSII.     

Environmental stress inhibits the synthesis de novo of proteins involved in the photodamage-repair cycle of Photosystem II in Synechocystis sp. PCC 6803

The Photosystem II complex (PSII) is susceptible to inactivation by strong light, and the inactivation caused by strong light is referred to as photoinactivation or photoinhibition. In photosynthetic organisms, photoinactivated PSII is rapidly repaired and the extent of photoinactivation reflects the balance between the light-induced damage (photodamage) to PSII and the repair of PSII. In this study, we examined these two processes separately and quantitatively under stress conditions in the cyanobacterium Synechocystis sp. PCC 6803. The rate of photodamage was proportional to light intensity over a range of light intensities from 0 to 2000 μE m⁻² s⁻¹, and this relationship was not affected by environmental factors, such as salt stress, oxidative stress due to H₂O₂, and low temperature. The rate of repair also depended on light intensity. It was high under weak light and reached a maximum of 0.1 min⁻¹ at 300 μE m⁻² s⁻¹. By contrast to the rate of photodamage, the rate of repair was significantly reduced by the above-mentioned environmental factors. Pulse-labeling experiments with radiolabeled methionine revealed that these environmental factors inhibited the synthesis de novo of proteins. Such proteins included the D1 protein which plays an important role in the photodamage-repair cycle. These observations suggest that the repair of PSII under environmental stress might be the critical step that determines the outcome of the photodamage-repair cycle.     

<Emphasis Type="Italic">Rhodobacter</Emphasis> sp. Rb3, an aerobic anoxygenic phototroph which thrives in the polyextreme ecosystem of the Salar de Huasco,in the Chilean Altiplano

The Salar de Huasco is an evaporitic basin located in the Chilean Altiplano, which presents extreme environmental conditions for life, i.e. high altitude (3800 m.a.s.l.), negative water balance, a wide salinity range, high daily temperature changes and the occurrence of the highest registered solar radiation on the planet (>?1200 W m^?2). This ecosystem is considered as a natural laboratory to understand different adaptations of microorganisms to extreme conditions. Rhodobacter, an anoxygenic aerobic phototrophic bacterial genus, represents one of the most abundant groups reported based on taxonomic diversity surveys in this ecosystem. The bacterial mat isolate Rhodobacter sp. strain Rb3 was used to study adaptation mechanisms to stress-inducing factors potentially explaining its success in a polyextreme ecosystem. We found that the Rhodobacter sp. Rb3 genome was characterized by a high abundance of genes involved in stress tolerance and adaptation strategies, among which DNA repair and oxidative stress were the most conspicuous. Moreover, many other molecular mechanisms associated with oxidative stress, photooxidation and antioxidants; DNA repair and protection; motility, chemotaxis and biofilm synthesis; osmotic stress, metal, metalloid and toxic anions resistance; antimicrobial resistance and multidrug pumps; sporulation; cold shock and heat shock stress; mobile genetic elements and toxin–antitoxin system were detected and identified as potential survival mechanism features in Rhodobacter sp. Rb3. In total, these results reveal a wide set of strategies used by the isolate to adapt and thrive under environmental stress conditions as a model of polyextreme environmental resistome.     

Differential Expression of Proteins in Response to Molybdenum Deficiency in Winter Wheat Leaves Under Low-Temperature Stress

Molybdenum (Mo) is an essential micronutrient for plants. To obtain a better understanding of the molecular mechanisms of cold resistance enhanced by molybdenum application in winter wheat, we applied a proteomic approach to investigate the differential expression of proteins in response to molybdenum deficiency in winter wheat leaves under low-temperature stress. Of 13 protein spots that were identified, five spots were involved in the light reaction of photosynthesis, five were involved in the dark reaction of photosynthesis, and three were highly involved in RNA binding and protein synthesis. Before the application of cold stress, four differentially expressed proteins between the Mo deficiency (?Mo) vs. Mo application (+Mo) comparison are involved in carbon metabolism and photosynthetic electron transport. After 48 h of cold stress, nine differentially expressed proteins between the ?Mo vs. +Mo comparison are involved in carbon metabolism, photosynthetic electron transport, RNA binding, and protein synthesis. Under ?Mo condition, cold stress induced a more than twofold decrease in the accumulation of six differential proteins including ribulose bisphosphate carboxylase large-chain precursor, phosphoglycerate kinase, cp31BHv, chlorophyll a/b-binding protein, ribulose bisphosphate carboxylase small subunit, and ribosomal protein P1, whereas under +Mo condition cold stress only decreased the expression of RuBisCO large subunit, suggesting that Mo application might contribute to the balance or stability of these proteins especially under low-temperature stress and that Mo deficiency has greater influence on differential protein expression in winter wheat after low-temperature stress. Further investigations showed that Mo deficiency decreased the concentrations of chlorophyll a, chlorophyll b, and carotenoids; the maximum net photosynthetic rate; the apparent quantum yield; and carboxylation efficiency, even before the application of the cold stress, although the decrease rates were greater after 48 h of cold treatment, which is consistent with changes in the expressions of differential proteins in winter wheat under low-temperature stress. These findings provide some new evidence that Mo might be involved in the light and dark reaction of photosynthesis and protein synthesis.     

Genomic investigation of the system for selenocysteine incorporation in the bacterial domain

The Photosystem II complex (PSII) is susceptible to inactivation by strong light, and the inactivation caused by strong light is referred to as photoinactivation or photoinhibition. In photosynthetic organisms, photoinactivated PSII is rapidly repaired and the extent of photoinactivation reflects the balance between the light-induced damage (photodamage) to PSII and the repair of PSII. In this study, we examined these two processes separately and quantitatively under stress conditions in the cyanobacterium Synechocystis sp. PCC 6803. The rate of photodamage was proportional to light intensity over a range of light intensities from 0 to 2000 microE m(-2) s(-1), and this relationship was not affected by environmental factors, such as salt stress, oxidative stress due to H2O2, and low temperature. The rate of repair also depended on light intensity. It was high under weak light and reached a maximum of 0.1 min(-1) at 300 microE m(-2) s(-1). By contrast to the rate of photodamage, the rate of repair was significantly reduced by the above-mentioned environmental factors. Pulse-labeling experiments with radiolabeled methionine revealed that these environmental factors inhibited the synthesis de novo of proteins. Such proteins included the D1 protein which plays an important role in the photodamage-repair cycle. These observations suggest that the repair of PSII under environmental stress might be the critical step that determines the outcome of the photodamage-repair cycle.     

Singlet oxygen-mediated and EXECUTER-dependent signalling and acclimation of Arabidopsis thaliana exposed to light stress

Plants respond to environmental changes by acclimation that activates defence mechanisms and enhances the plant''s resistance against a subsequent more severe stress. Chloroplasts play an important role as a sensor of environmental stress factors that interfere with the photosynthetic electron transport and enhance the production of reactive oxygen species (ROS). One of these ROS, singlet oxygen (¹O₂), activates a signalling pathway within chloroplasts that depends on the two plastid-localized proteins EXECUTER 1 and 2. Moderate light stress induces acclimation protecting photosynthetic membranes against a subsequent more severe high light stress and at the same time activates ¹O₂-mediated and EXECUTER-dependent signalling. Pre-treatment of Arabidopsis seedlings with moderate light stress confers cross-protection against a virulent Pseudomonas syringae strain. While non-pre-acclimated seedlings are highly susceptible to the pathogen regardless of whether ¹O₂- and EXECUTER-dependent signalling is active or not, pre-stressed acclimated seedlings without this signalling pathway lose part of their pathogen resistance. These results implicate ¹O₂- and EXECUTER-dependent signalling in inducing acclimation but suggest also a contribution by other yet unknown signalling pathways during this response of plants to light stress.     

Proteomic analysis of Synechocystis sp. PCC6803 responses to low-temperature and high light conditions

The global changes in protein expression of Synechocystis sp. PCC6803, a photosynthetic bacterium for the production of secondary metabolites as a green cell factory, were investigated by proteome separation and a subsequent tandem mass spectrometry. Two different proteome separation techniques, strong cation exchange chromatography and off-gel electrophoresis, were applied. The combination of the two proteome separation techniques enabled the comparative analysis of the differential regulation of the Synechocystis proteome in response to two different environmental factors, temperature and light. A total of 1,483 proteins were identified, which represent over 40% of the genes in Synechocystis. Our data showed that fatty acid metabolism was inhibited by (3R)-hydroxymyristol acyl carrier protein dehydrase (Sll1605) under low temperature conditions. The expression of UDP-N-acetylglucosamine acyltransferase (Sll0379) and 3-O-[3-hydroxymyristoyl] glucosamine N-acyltransferase (Slr0776), which is involved in lipopolysaccharide metabolism, was not observed under high light conditions. Under high light exposure, proteins related to iron-sulfur metabolism were detected, which may be responsible for maintaining the redox potential of the photosystem. High light under low temperature caused severe damage to the photosystem. Some of the responses to these stresses were similar to those previously reported for other photosynthetic organisms. Notably, this study revealed the followings: (i) low temperature inhibits fatty acid synthesis; (ii) high light inhibits lipopolysaccharides synthesis and stimulates the expression of iron-sulfur related proteins; and (iii) high light under low temperature induces the photorespiratory cycle. The global proteomic analysis clearly showed that stress conditions such as low temperature and/or high light induce cellular metabolisms related with the protection of their photosystems in the model microalga Synechocystis sp. PCC6803.     

Environmentally modulated phosphorylation and dynamics of proteins in photosynthetic membranes

Recent advances in vectorial proteomics of protein domains exposed to the surface of photosynthetic thylakoid membranes of plants and the green alga Chlamydomonas reinhardtii allowed mapping of in vivo phosphorylation sites in integral and peripheral membrane proteins. In plants, significant changes of thylakoid protein phosphorylation are observed in response to stress, particularly in photosystem II under high light or high temperature stress. Thylakoid protein phosphorylation in the algae is much more responsive to the ambient redox and light conditions, as well as to CO₂ availability. The light-dependent multiple and differential phosphorylation of CP29 linker protein in the green algae is suggested to control photosynthetic state transitions and uncoupling of light harvesting proteins from photosystem II under high light. The similar role for regulation of the dynamic distribution of light harvesting proteins in plants is proposed for the TSP9 protein, which together with other recently discovered peripheral proteins undergoes specific environment- and redox-dependent phosphorylation at the thylakoid surface. This review focuses on the environmentally modulated reversible phosphorylation of thylakoid proteins related to their membrane dynamics and affinity towards particular photosynthetic protein complexes.     

植物光合系统对高温胁迫的响应机制

温度变化是影响植物生长和发育的一个非常重要的因素,而光合作用是植物对温度变化最为敏感的生理过程.高温胁迫给植物光合器官造成了严重的危害,但在高温胁迫下,植物并不是消极被动的,并且能够在生理生化及分子水平上发生各种变化来渡过逆境.本文结合当今国内外研究进展,从光合系统热量耗散与光合修复的相关因素,如类囊体膜上相关蛋白,热激蛋白,水杨酸,抗过氧化物酶及抗坏血酸等几个方面展开分析,阐述了植物光合系统对高温胁迫的防御机制,并对今后的研究方向进行了探讨和展望.     

Enhanced photosynthesis and redox energy production contribute to salinity tolerance in Dunaliella as revealed by homology-based proteomics

Salinity is a major limiting factor for the proliferation of plants and inhibits central metabolic activities such as photosynthesis. The halotolerant green alga Dunaliella can adapt to hypersaline environments and is considered a model photosynthetic organism for salinity tolerance. To clarify the molecular basis for salinity tolerance, a proteomic approach has been applied for identification of salt-induced proteins in Dunaliella. Seventy-six salt-induced proteins were selected from two-dimensional gel separations of different subcellular fractions and analyzed by mass spectrometry (MS). Application of nanoelectrospray mass spectrometry, combined with sequence-similarity database-searching algorithms, MS BLAST and MultiTag, enabled identification of 80% of the salt-induced proteins. Salinity stress up-regulated key enzymes in the Calvin cycle, starch mobilization, and redox energy production; regulatory factors in protein biosynthesis and degradation; and a homolog of a bacterial Na(+)-redox transporters. The results indicate that Dunaliella responds to high salinity by enhancement of photosynthetic CO(2) assimilation and by diversion of carbon and energy resources for synthesis of glycerol, the osmotic element in Dunaliella. The ability of Dunaliella to enhance photosynthetic activity at high salinity is remarkable because, in most plants and cyanobacteria, salt stress inhibits photosynthesis. The results demonstrated the power of MS BLAST searches for the identification of proteins in organisms whose genomes are not known and paved the way for dissecting molecular mechanisms of salinity tolerance in algae and higher plants.     

Citrus flavanone metabolites significantly modulate global proteomic profile in pancreatic β-cells under high-glucose-induced metabolic stress

Hesperidin and narirutin are the major citrus flavanones. Several studies have associated these compounds with pancreatic β-cell survival through their capacity to reduce oxidative stress, inflammation, and inhibit apoptosis. However, the molecular mechanisms of action of flavanones in pancreatic β-cells under high-glycemic stress is still largely unknown. Therefore, this study aimed to decipher molecular mechanisms of flavanone metabolites in pancreatic β-cells treated with high glucose concentration using untargeted shotgun proteomics. We identified 569 proteins differentially expressed in cells exposed to hesperetin 7-glucuronide (H7G) and 265 in cells exposed to 3-(4′-hydroxyphenyl) propanoic acid (PA). Comparison of global proteomic profiles suggest that these metabolites could counteract changes in protein expression induced by high glucose stress. The bioinformatic analyses suggested that H7G and PA modulated the expression of proteins involved in cell adhesion, cell signaling, metabolism, inflammation, and protein processing in endoplasmic reticulum (ER) pathways. Taken together, this study suggests that H7G and PA can modulate the expression of proteins that may prevent dysfunction of pancreatic β-cells under stress induced by high glucose.     

Two major metabolic factors for an efficient NADP-malic enzyme type C4 photosynthesis

Compared to the large number of studies focused on the factors controlling C₃ photosynthesis efficiency, there are relatively fewer studies of the factors controlling photosynthetic efficiency in C₄ leaves. Here, we used a dynamic systems model of C₄ photosynthesis based on maize (Zea mays) to identify features associated with high photosynthetic efficiency in NADP-malic enzyme (NADP-ME) type C₄ photosynthesis. We found that two additional factors related to coordination between C₄ shuttle metabolism and C₃ metabolism are required for efficient C₄ photosynthesis: (1) accumulating a high concentration of phosphoenolpyruvate through maintaining a large PGA concentration in the mesophyll cell chloroplast and (2) maintaining a suitable oxidized status in bundle sheath cell chloroplasts. These identified mechanisms are in line with the current cellular location of enzymes/proteins involved in the starch synthesis, the Calvin–Benson cycle and photosystem II of NADP-ME type C₄ photosynthesis. These findings suggested potential strategies for improving C₄ photosynthesis and engineering C₄ rice.

High levels of PGA and PEP in mesophyll cell chloroplasts and a suitable oxidation state in bundle sheath cell chloroplasts are the requirements for efficient C₄ photosynthesis.     

Comparative Physiological and Proteomic Analysis Reveals the Leaf Response to Cadmium-Induced Stress in Poplar (Populus yunnanensis)

Excess amounts of heavy metals are important environmental pollutants with significant ecological and nutritional effects. Cdmium (Cd) is of particular concern because of its widespread occurrence and high toxicity. We conducted physiological and proteomic analyses to improve our understanding of the responses of Populus yunnanensis to Cd stress. The plantlets experienced two apparent stages in their response to Cd stress. During the first stage, transiently induced defense-response molecules, photosynthesis- and energy-associated proteins, antioxidant enzymes and heat shock proteins (HSPs) accumulated to enhance protein stability and establish a new cellular homeostasis. This activity explains why plant photosynthetic capability during this period barely changed. During the second stage, a decline of ribulose-1, 5-bisphosphate carboxylase (RuBisCO) and HSP levels led to imbalance of the plant photosynthetic system. Additionally, the expression of Mitogen-activated protein kinase 3 (MPK3), Mitogen-activated protein kinase 6 (MPK6) and a homeobox-leucine zipper protein was higher in the second stage. Higher expression of caffeoyl-CoA O-methyltransferase (CCoAOMT) may regulate plant cell wall synthesis for greater Cd storage. These genes may be candidates for further research and use in genetic manipulation of poplar tolerance to Cd stress.     

Inhibition of the repair of Photosystem II by oxidative stress in cyanobacteria

The activity of Photosystem II (PS II) is severely restricted by a variety of environmental factors and, under environmental stress, is determined by the balance between the rate of damage to PS II and the rate of the repair of damaged PS II. The effects of oxidative stress on damage and repair can be examined separately, and it appears that, while light can damage PS II directly, oxidative stress acts primarily by inhibiting the repair of PS II. Studies in cyanobacteria have demonstrated that oxidative stress suppresses the de novo synthesis of proteins, in particular, the D1 protein, which is required for the repair of PS II.     

Photosynthetic performance of Anabaena variabilis PCC 7937 under simulated solar radiation

In vivo chlorophyll fluorescence analysis reflecting the photosystem II functionality was investigated in the cyanobacterium Anabaena variabilis PCC 7937 under simulated solar radiation in a combination with various cut-off filters (WG 280, WG 295, WG 305, WG 320, WG 335, WG 345, and GG 400) to assess the effects of photosynthetically active radiation (PAR), ultraviolet-A (UV-A), and ultraviolet-B (UV-B) radiations on photosynthesis. The photosynthetic activity (PA) was severely inhibited immediately after 10 min of exposure to high PAR, UV-A, and UV-B radiations compared with low PAR grown control samples. After 1 h of exposure, PA of 17.5 ± 2.9% was detected in the high PAR exposed samples compared with the control, while only a trace or no PA was observed in the presence of ultraviolet radiation (UVR). A recovery of PA was recorded after 2 h of the exposure, which continued for next 4, 8, 12, and 24 h. After 24 h of the exposure, PA of 57.5 ± 1.9%, 36.1 ± 11.7%, 23.5 ± 3.3%, 22.3 ± 5.2%, 20.8 ± 6.7%, 13.2 ± 6.6%, and 21.6 ± 9.5% was observed compared with the control sample in 400, 345, 335, 320, 305, 295, and 280 nm cut-off filters-covered samples, respectively. The relative electron transport rate, measured after 24 h exposure, showed also a disturbance in electron transfer between the two photosystems under the high PAR and UVR treatments relative to the control samples, suggesting the inhibition of photosynthesis. This study suggests that both high PAR and UVR inhibited the photosynthetic performance of A. variabilis PCC 7937 by damaging the photosynthetic apparatus, however, photoprotective mechanisms evolved by the organism allowed an immediate repair of ecologically important machinery, and enabled its survival.     

Native architecture and acclimation of photosynthetic membranes in a fast-growing cyanobacterium

Efficient solar energy conversion is ensured by the organization, physical association, and physiological coordination of various protein complexes in photosynthetic membranes. Here, we visualize the native architecture and interactions of photosynthetic complexes within the thylakoid membranes from a fast-growing cyanobacterium Synechococcus elongatus UTEX 2973 (Syn2973) using high-resolution atomic force microscopy. In the Syn2973 thylakoid membranes, both photosystem I (PSI)-enriched domains and crystalline photosystem II (PSII) dimer arrays were observed, providing favorable membrane environments for photosynthetic electron transport. The high light (HL)-adapted thylakoid membranes accommodated a large amount of PSI complexes, without the incorporation of iron-stress-induced protein A (IsiA) assemblies and formation of IsiA–PSI supercomplexes. In the iron deficiency (Fe⁻)-treated thylakoid membranes, in contrast, IsiA proteins densely associated with PSI, forming the IsiA–PSI supercomplexes with varying assembly structures. Moreover, type-I NADH dehydrogenase-like complexes (NDH-1) were upregulated under the HL and Fe⁻ conditions and established close association with PSI complexes to facilitate cyclic electron transport. Our study provides insight into the structural heterogeneity and plasticity of the photosynthetic apparatus in the context of their native membranes in Syn2973 under environmental stress. Advanced understanding of the photosynthetic membrane organization and adaptation will provide a framework for uncovering the molecular mechanisms of efficient light harvesting and energy conversion.