Comparative proteomics analysis of salt response reveals sex-related photosynthetic inhibition by salinity in Populus cathayana cuttings

Differences in ecophysiological responses of Populus euphratica females and males exposed to salinity and alkali stress

Soil salinity is usually accompanied by alkalization in northwest China, and they both negatively impact plant growth and result in severe ecological problems. Some studies have reported tree responses to salinity or alkali stress alone, however, the interactive salinity and alkali effects are still unclear, especially in dioecious trees. In this study, we measured growth, morphology, leaf stomata, gas exchange, carbon isotope composition (δ¹³C), total soluble sugar and starch contents, Na⁺ accumulation and allocation, oxidative stress, and antioxidants of female and male Populus euphratica seedlings in response to salinity, alkali and their interaction. Our study showed no significant sexual differences in studied traits under control conditions. In addition, P. euphratica females showed greater inhibitory and negative effects, such as bigger decreases in growth and gas exchange, lower stomatal density and water use efficiency (as described by δ¹³C), and lower levels of soluble sugars and antioxidant enzyme activities compared with males under salinity, alkali and interactive stress conditions. Furthermore, P. euphratica males had a greater ability of ion exclusion and Na ⁺ transport restriction. For example, males allocated more Na⁺ to stems and roots than females, whereas females had higher Na⁺ contents in leaves under stress conditions. In conclusion, our results indicated that P. euphratica males have superior resistance and they perform better than females under salinity, alkali and their interactive stress conditions.

Molecular responses to salinity stress in Salix matsudana (Koidz) females and males

Sexual dimorphism has commonly been found in many species. The phenotypes of Salix matsudana females and males are different under salinity stress. An F₁ population was selected to compare the differences between males and females. As a result, males showed stronger roots and heavier dry weights than females. The unique molecular mechanisms of males and females under salinity stress were further analyzed based on the root transcriptome of males and females. Both males and females up-regulated systemic acquired resistance genes, such as ADH and oxygenase-related genes, to resist salt. Moreover, many other abiotic stress response genes were up-regulated in males to adjust to salinity stress, while females showed more down-regulation of nitrogen metabolism-related genes to decrease the harm from salinity stress. The research on salinity tolerance in Salix matsudana males and females would help to further understand sexual dimorphism under selection pressure and provide benefits to the ecological environment.

The Glutathione S-Transferase PtGSTF1 Improves Biomass Production and Salt Tolerance through Regulating Xylem Cell Proliferation, Ion Homeostasis and Reactive Oxygen Species Scavenging in Poplar

Glutathione S-transferases (GSTs) play an essential role in plant cell detoxification and secondary metabolism. However, their accurate functions in the growth and response to abiotic stress in woody plants are still largely unknown. In this work, a Phi class Glutathione S-transferase encoding gene PtGSTF1 was isolated from poplar (P. trichocarpa), and its biological functions in the regulation of biomass production and salt tolerance were investigated in transgenic poplar. PtGSTF1 was ubiquitously expressed in various tissues and organs, with a predominant expression in leaves and inducible expression by salt stress. Transgenic poplar overexpressing PtGSTF1 showed improved shoot growth, wood formation and improved salt tolerance, consistent with the increased xylem cell number and size under normal condition, and the optimized Na⁺ and K⁺ homeostasis and strengthened reactive oxygen species scavenging during salt stress. Further transcriptome analyses demonstrated that the expressions of genes related to hydrolase, cell wall modification, ion homeostasis and ROS scavenging were up- or down-regulated in transgenic plants. Our findings imply that PtGSTF1 improves both biomass production and salt tolerance through regulating hydrolase activity, cell wall modification, ion homeostasis and ROS scavenging in transgenic poplar, and that it can be considered as a useful gene candidate for the genetic breeding of new tree varieties with improved growth under salt stress conditions.

Molecular cloning and oxidative-stress responses of a novel Phi class glutathione S-transferase (GSTF) gene in the freshwater algae Closterium ehrenbergii

Glutathione S-transferases (GSTs) belong to a family of enzymes involved in diverse biological processes, including detoxification and protection against oxidative damage. Here, we determined the full-length sequence (915 bp) of a novel Phi class cytosolic glutathione S-transferase (GSTF) gene from the green algae Closterium ehrenbergii. We examined the gene structure and expression patterns in response to metals and endocrine disrupting chemicals (EDCs). It was significantly upregulated by metals, but responded differently to EDCs. The highest up-regulation of CeGSTF was registered under 0.1 mg/L CuCl₂ and 0.01 mg/L CuSO₄ treatments. In a 72-h course experiment with treatment of 0.1 mg/L CuCl₂ , CeGSTF was dramatically induced at 6 h, and then gradually decreased with increasing exposure time. This was consistent with the increase in both GST activity and ROS production in copper-treated cells. These results suggest that CeGSTF may be involved in detoxification mechanisms associated with oxidative stress in green algae.

Sex-specific photosynthetic capacity and Na+ homeostasis in Populus euphratica exposed to NaCl stress and AMF inoculation

Soil salinity and associated land degradation are major ecological problems. Excess Na⁺ ions in soil impede the plant photosynthetic process and Na⁺ homeostasis status. Arbuscular mycorrhizal fungi (AMF) can alleviate salt stress in host plants. Although a number of studies have demonstrated that Na⁺ accumulation is decreased by mycorrhizae, the molecular mechanisms involved have received little attention from researchers. Populus euphratica is a typical natural woody tree with excellent salt tolerance. Due to its symbiosis forming capability with AMF, we explored the influence of Funneliformis mosseae on the growth, photosynthesis, and expression of three genes involved in Na⁺ homeostasis within dioecious P. euphratica under salt stress. The results indicated that salt stress significantly increases Na⁺ contents and inhibits growth status and photosynthetic capacity, especially in females. However, AMF had positive effects on the growth status, photosynthetic capacity and Na⁺ homeostasis, especially in males. The expression levels of NHX1 in shoots and HKT1 and SOS1 in roots, all of which are involved in Na⁺ homeostasis, were upregulated by F. mosseae under salt stress. For males, the beneficial effect of AMF centered on extruding, sequestering and long-distance transporting of Na⁺ ions . For females, the beneficial effect of AMF centered on extruding excessive Na⁺.

SWATH-MS based quantitive proteomics reveal regulatory metabolism and networks of androdioecy breeding system in Osmanthus fragrans

BACKGROUND

The fragrant flower plant Osmanthus fragrans has an extremely rare androdioecious breeding system displaying the occurrence of males and hermaphrodites in a single population, which occupies a crucial intermediate stage in the evolutionary transition between hermaphroditism and dioecy. However, the molecular mechanism of androdioecy plant is very limited and still largely unknown.

RESULTS

Here, we used SWATH-MS-based quantitative approach to study the proteome changes between male and hermaphroditic O. fragrans pistils. A total of 428 proteins of diverse functions were determined to show significant abundance changes including 210 up-regulated and 218 down-regulated proteins in male compared to hermaphroditic pistils. Functional categorization revealed that the differentially expressed proteins (DEPs) primarily distributed in the carbohydrate metabolism, secondary metabolism as well as signaling cascades. Further experimental analysis showed the substantial carbohydrates accumulation associated with promoted net photosynthetic rate and water use efficiency were observed in purplish red pedicel of hermaphroditic flower compared with green pedicel of male flower, implicating glucose metabolism serves as nutritional modulator for the differentiation of male and hermaphroditic flower. Meanwhile, the entire upregulation of secondary metabolism including flavonoids, isoprenoids and lignins seem to protect and maintain the male function in male flowers, well explaining important feature of androdioecy that aborted pistil of a male flower still has a male function. Furthermore, nine selected DEPs were validated via gene expression analysis, suggesting an extra layer of post-transcriptional regulation occurs during O. fragrans floral development.

CONCLUSION

Taken together, our findings represent the first SWATH-MS-based proteomic report in androdioecy plant O. fragrans, which reveal carbohydrate metabolism, secondary metabolism and post-transcriptional regulation contributing to the androdioecy breeding system and ultimately extend our understanding on genetic basis as well as the industrialization development of O. fragrans.

Sexual Differences in Physiological and Transcriptional Responses to Salinity Stress of Salix linearistipularis

Willow (Salix), a dioecious plant, is an important ornamental tree species in the world. Salix linearistipularis, a perennial woody plant species naturally distributed on the Songnen Plain saline-alkali land in northeast China, has a high saline condition. To study the sexual differences of S. linearistipularis in salinity tolerance, the physiological and transcriptional responses to salinity were compared between female and male cuttings. Under salinity stress, the female leaves exhibited higher superoxide dismutase and peroxidase activities and photosynthetic capacity, and lower H2O2 contents than those of male leaves. Under salinity stress, sodium (Na+) accumulation in female leaves was lower than that in the male leaves. The non-invasive micro-test showed that the net Na+ efflux in the salt-treated female roots was higher than that in male roots. Physiological responses revealed that female cuttings were more tolerant than males, which may be mainly due to females having lower leaf Na+ accumulation and higher root Na+ efflux capacity than males. Transcriptional analyses showed that 108 differentially expressed salt-responsive genes were identified in both female and male roots; most of these showed sexual differences in expression patterns under salinity stress. RNA-seq combined with qPCR analysis showed that the salt-induced expression of four Na+/H+ antiporter (NHX) genes (SlNHX3, 5, 6, 7) in female roots was higher than that in male roots. Transcriptional analyses revealed that the higher Na+ efflux capacity in female roots than in male roots may be closely related to the differential expression of salt-responsive genes, especially NHX genes.

Comparative Proteomic Analysis of Two Manilkara Species Leaves Under NaCl Stress

Background:

Salinity is a major environmental limiting factor, which affect agricultural production. The two Manilkara seedlings (M. roxburghiana and M. zapota) with high economic importance, could not adapt well to higher soil salinity and little is known about their proteomic mechanisms.

Objectives:

The mechanisms responsible for the effects of salinity on the two Manilkara species leaves were examined by means of proteomic analysis.

Material and Methods:

The seedlings were cultivated in a greenhouse and treated with NaCl. Leaves of control and the salt-stressed seedlings were sampled for phenol protein extraction. Proteins were separated by two-dimensional gel electrophoresis coupled with mass spectroscopy to study the change of proteins under different NaCl concentration.

Results:

For M. roxburghiana leaves, 21 protein spots exhibited significant abundance variations between the control and the 6‰, 8‰ NaCl treatments, of these 13 proteins were identified. They included L-ascorbate peroxidase, chloroplast carbonic anhydrase, phosphoglycerate kinase, 5 heat-shock proteins(HSPs) which were all down- regulated; For M. zapota leaves, 35 protein spots exhibited significant abundance variations, then 24 proteins were identified, including 7 down-regulated HSPs as well as glyceraldehyde-3-phosphate dehydrogenase, Cell division protein, putative mitochondrial NAD-dependent malate dehydrogenase, ATP synthase, Rubisco large subunit-binding protein, Cytochrome c peroxidase.

Conclusions:

Based on the common identified proteins between the two M. species, our results indicated that the identificated proteins in the two Manilkara species were involved in carbohydrate metabolism, photosynthesis, defense and stress. HSPs exhibited variation strictly related to NaCl stress. The down-regulated HSPs meant the function to repair cells that have suffered damage weaken during stress process. Furthermore, except for HSP70 in M. zapota leaves, the HSPs in the two species were all small heat shock proteins (sHSPs) with molecular weights ranging from 15 to 42 kDa.

Connecting salt stress signalling pathways with salinity-induced changes in mitochondrial metabolic processes in C3 plants

Salinity exerts a severe detrimental effect on crop yields globally. Growth of plants in saline soils results in physiological stress, which disrupts the essential biochemical processes of respiration, photosynthesis, and transpiration. Understanding the molecular responses of plants exposed to salinity stress can inform future strategies to reduce agricultural losses due to salinity; however, it is imperative that signalling and functional response processes are connected to tailor these strategies. Previous research has revealed the important role that plant mitochondria play in the salinity response of plants. Review of this literature shows that 2 biochemical processes required for respiratory function are affected under salinity stress: the tricarboxylic acid cycle and the transport of metabolites across the inner mitochondrial membrane. However, the mechanisms by which components of these processes are affected or react to salinity stress are still far from understood. Here, we examine recent findings on the signal transduction pathways that lead to adaptive responses of plants to salinity and discuss how they can be involved in and be affected by modulation of the machinery of energy metabolism with attention to the role of the tricarboxylic acid cycle enzymes and mitochondrial membrane transporters in this process.

Proteomic analysis of Camellia sinensis (L.) reveals a synergistic network in the response to drought stress and recovery

Drought is a crucial limiting factor for tea yield and quality. To systematically characterize the molecular response of tea plants to drought stress and its capacity to recover, we used iTRAQ-based comparative proteomic approach to investigate the effects of drought on protein expression profiles in tea seedlings subjected to different drought treatments. A total of 3274 proteins were identified, of which 2169 and 2300 showed differential expressions during drought and recovery, respectively. Functional annotation showed that multiple biological processes were regulated, suggesting that tea plants probably employed multiple and synergistic resistance mechanisms in dealing with drought stress. Hierarchical clustering showed that chlorophyll a/b-binding proteins were up-regulated in DB and RE, suggesting that tea plants might regulate expression of chlorophyll a/b-binding proteins to maintain the photosystem II function during drought stress. Abundant proteins involved in sulfur-containing metabolite pathways, such as glutathione, taurine, hypotaurine, methionine, and cysteine, changed significantly during drought stress. Among them, TL29 interacted with LHCb6 to connect S-containing metabolites with chlorophyll a/b-binding proteins. This suggests that sulfur-containing compounds play important roles in the response to drought stress in tea plants. In addition, the expression of PAL was up-regulated in DA and down-regulated in DB. Cinnamyl alcohol dehydrogenase, caffeic acid O-methyltransferase, and 4-coumarate-CoA ligase also showed significant changes in expression levels, which regulated the biosynthesis of polyphenols. The results indicate that slight drought stress might promote polyphenol biosynthesis, while serious drought stress leads to inhibition. The expression of lipoxygenase and short-chain dehydrogenase increased during slight drought stress and some volatile metabolite pathways were enriched, indicating that drought stress might affect the tea aroma. The study provides valuable information that will lay the foundation for studies investigating the functions of drought response genes in tea leaves.

Sex-Specific Response to Stress in Populus

Populus is an effective model for genetic studies in trees. The genus Populus includes dioecious species, and the differences exhibited in males and females have been intensively studied. This review focused on the distinctions between male and female poplar and aspen plants under stress conditions, such as drought, salinity, heavy metals, and nutrient deficiency on morphological, physiological, proteome, and gene expression levels. In most studies, males of Populus species were more adaptive to the majority of the stress conditions and showed less damage, better growth, and higher photosynthetic capacity and antioxidant activity than that of the females. However, in two recent studies, no differences in non-reproductive traits were revealed for male and female trees. This discrepancy of the results could be associated with experimental design: different species and genotypes, stress conditions, types of plant materials, sampling sizes. Knowledge of sex-specific differences is crucial for basic and applied research in Populus species.

Comparative photochemistry activity and antioxidant responses in male and female Populus cathayana cuttings inoculated with arbuscular mycorrhizal fungi under salt

We investigated the impact of arbuscular mycorrhizal fungi (AMF) on the morphology and physiology of two genders of the typical dioecious plant Populus cathayana under salt stress. We conducted a pot experiment containing seedlings of the two genders that were subjected to salt or non-salt and filled with soil that was either inoculated with Rhizophagus intraradices or not. The results showed that males had higher mycorrhizal dependency than females. Salt stress decreased growth, the relative water content and chlorophyll fluorescence. Meanwhile, salt increased the superoxide radical (O₂⁻), and hydrogen peroxide (H₂O₂) contents and antioxidant enzyme activities. Mycorrhizal male seedlings performed better than females in shoot morphological growth under both conditions and in chlorophyll fluorescence parameters, O₂⁻ and H₂O₂ contents, MDA concentration, proline content and antioxidant enzymes activities under salt stress. In females, under saline conditions, a lower MDA concentration and H₂O₂, O₂⁻ and proline contents were observed in the leaves and roots. In addition, inoculated female plants performed better in chlorophyll fluorescence parameters than non-inoculated plants. AMF inoculation had either slight or no effects on the performance of females. These findings suggested that when subjected to stress and AMF, differences in the genders existed, followed by the alleviation of the damage to P. cathayana by AMF via improving growth and photosynthesis and antioxidant systems under salt stress.

Role of Proteomics in Crop Stress Tolerance

Plants often experience various biotic and abiotic stresses during their life cycle. The abiotic stresses include mainly drought, salt, temperature (low/high), flooding and nutritional deficiency/excess which hamper crop growth and yield to a great extent. In view of a projection 50% of the crop loss is attributable to abiotic stresses. However, abiotic stresses cause a myriad of changes in physiological, molecular and biochemical processes operating in plants. It is now widely reported that several proteins respond to these stresses at pre- and post-transcriptional and translational levels. By knowing the role of these stress inducible proteins, it would be easy to comprehensively expound the processes of stress tolerance in plants. The proteomics study offers a new approach to discover proteins and pathways associated with crop physiological and stress responses. Thus, studying the plants at proteomic levels could help understand the pathways involved in stress tolerance. Furthermore, improving the understanding of the identified key metabolic proteins involved in tolerance can be implemented into biotechnological applications, regarding recombinant/transgenic formation. Additionally, the investigation of identified metabolic processes ultimately supports the development of antistress strategies. In this review, we discussed the role of proteomics in crop stress tolerance. We also discussed different abiotic stresses and their effects on plants, particularly with reference to stress-induced expression of proteins, and how proteomics could act as vital biotechnological tools for improving stress tolerance in plants.

Effects of drought and salt-stresses on gene expression in Caragana korshinskii seedlings revealed by RNA-seq

BACKGROUND

Drought and soil salinity are major abiotic stresses. The mechanisms of stress tolerance have been studied extensively in model plants. Caragana korshinskii is characterized by high drought and salt tolerance in northwestern China; unique patterns of gene expression allow it to tolerate the stress imposed by dehydration and semi-desert saline soil. There have, however, been no reports on the differences between C. korshinskii and model plants in the mechanisms underlying their drought and salt tolerance and regulation of gene expression.

RESULTS

Three sequencing libraries from drought and salt-treated whole-seedling- plants and the control were sequenced to investigate changes in the C. korshinskii transcriptome in response to drought and salt stresses. Of the 129,451 contigs, 70,662 (54.12 %) were annotated with gene descriptions, gene ontology (GO) terms, and metabolic pathways, with a cut-off E-value of 10(-5). These annotations included 56 GO terms, 148 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, and 25 Clusters of Orthologous Groups (COG). On comparison of the transcriptomes of the control, drought- and salt-treated plants, 1630 and 1521 contigs showed significant differences in transcript abundance under drought and salt stresses. Compared to the differentially expressed genes (DEGs) in drought- or salt-treated Arabidopsis in the database, 542 DEGs in drought-treated C. korshinskii and 529 DEGs in salt-treated samples were presumably unique to C. korshinskii. The transcription profiles revealed that genes related to transcription factors, protein kinases, and antioxidant enzymes are relevant to the tolerance of drought and salt stress in this species. The expression patterns of 38 randomly selected DEGs were confirmed by quantitative real-time PCR and were essentially consistent with the changes in transcript abundance identified by RNA-seq.

CONCLUSIONS

The present study identified potential genes involved in drought and salt tolerance in C. korshinskii, as well as many DEGs uniquely expressed in drought- or salt-treated C. korshinskii samples compared to Arabidopsis. To our knowledge, this study is the first exploration of the C. korshinskii transcriptome under drought and salt conditions, and these results will facilitate the discovery of specific stress-resistance-related genes in C. korshinskii, possibly leading to the development of novel plant cultivars through genetic engineering.

Proteomics, photosynthesis and salt resistance in crops: An integrative view

Salinity is a stressful condition that causes a significant decrease in crop production worldwide. Salt stress affects several photosynthetic reactions, including the modulation of several important proteins. Despite these effects, few molecular-biochemical markers have been identified and evaluated for their importance in improving plant salt resistance. Proteomics is a powerful tool that allows the analysis of multigenic events at the post-translational level that has been widely used to evaluate protein modulation changes in plants exposed to salt stress. However, these studies are frequently fragmented and the results regarding photosynthesis proteins in response to salinity are limited. These constraints could be related to the low number of important photosynthetic proteins differently modulated in response to salinity, as has been commonly revealed by conventional proteomics. In this review, we present an evaluation and perspective on the integrated application of proteomics for the identification of photosynthesis proteins to improve salt resistance. We propose the use of phospho-, thiol- and redox-proteomics, associated with the utilization of isolated chloroplasts or photosynthetic sub-organellar components. This strategy may allow the characterization of essential proteins, providing a better understanding of photosynthesis regulation. Furthermore, this may contribute to the selection of molecular markers to improve salt resistance in crops.

Sex-related differences in stress tolerance in dioecious plants: a critical appraisal in a physiological context

Sex-related differences in reproductive effort can lead to differences in vegetative growth and stress tolerance. However, do all dioecious plants show sex-related differences in stress tolerance? To what extent can the environmental context and modularity mask sex-related differences in stress tolerance? Finally, to what extent can physiological measurements help us understand secondary sexual dimorphism? This opinion paper aims to answer these three basic questions with special emphasis on developments in research in this area over the last decade. Compelling evidence indicates that dimorphic species do not always show differences in stress tolerance between sexes; and when sex-related differences do occur, they seem to be highly species-specific, with greater stress tolerance in females than males in some species, and the opposite in others. The causes of such sex-related species-specific differences are still poorly understood, and more physiological studies and diversity of plant species that allow comparative analyses are needed. Furthermore, studies performed thus far demonstrate that the expression of dioecy can lead to sex-related differences in physiological traits-from leaf gas exchange to gene expression-but the biological significance of modularity and sectoriality governing such differences has been poorly investigated. Future studies that consider the importance of modularity and sectoriality are essential for unravelling the mechanisms underlying stress adaptation in male and female plants growing in their natural habitat.

Salt stress response of membrane proteome of sugar beet monosomic addition line M14

Understanding how plants respond to and tolerate salt stress is important for engineering and breeding effort to boost plant productivity and bioenergy in an ever challenging environment. Sugar beet M14 line is a unique germplasm that contains genetic materials from Beta vulgaris L. and Beta corolliflora Zoss, and it exhibits tolerance to salt stress. Here we report the changes in membrane proteome of the M14 plants in response to salt stress (0, 200, 400mM NaCl) using an iTRAQ two-dimensional LC-MS/MS technology for quantitative proteomic analysis. In total, 274 proteins, mostly membrane proteins, were identified, and 50 proteins exhibited differential protein level changes, with 40 proteins increased and 10 decreased. The proteins were mainly involved in transport, metabolism, protein synthesis, photosynthesis, protein folding and degradation, signal transduction, stress and defense, energy, and cell structure. These results have revealed interesting mechanisms underlying the M14 response and tolerance to salt stress.

BIOLOGICAL SIGNIFICANCE

Sugar beet monosomic addition line M14 is a special variety with salt stress tolerance. Analysis of the M14 membrane proteome under salt stress may provide useful information regarding specific adaptive mechanisms underlying salt stress tolerance. Membrane proteins are known to play critical roles in salt stress signaling and adaptation. The purpose of this study was to identify significantly changed membrane proteins and determine their possible relevance to salt tolerance. The proteomic analysis of the M14 line revealed important molecular mechanisms that can be potentially applied to improving crop salt tolerance. This article is part of a Special Issue entitled: Proteomics in India.

Transcriptional profiling in dioecious plant Populus cathayana reveals potential and sex-related molecular adaptations to solar UV-B radiation

There is increasing evidence confirming that dioecious plants have evolved a series of sex-related physiological mechanisms allowing acclimation to environmental stresses, but few studies have attempted to thoroughly uncover the potential molecular regulation underlying these responses. Recently, we found in the dioecious plant, Populus cathayana, that males possess a greater tolerance to enhanced UV-B radiation than do females. To continue this work further, comparative transcriptome analyses were carried out. A total of 362 and 296 differentially expressed genes (DEGs) were detected in males and females, respectively. Similarly, as shown in previous studies, these DEGs were involved in a set of conserved functions and pathways related to UV-B stress, regardless of the sex. On the other hand, sex-related responses via transcriptome remodeling were detected, as changes in sex-related gene expression occurred in some pathways. For example, many DEGs involved in amino acid metabolism were mainly upregulated in males but downregulated in females. In some pathways, DEGs were expressed predominantly or exclusively in one sex. This may directly contribute to sex-related physiological responses. Taken together, our results not only provide strong evidence that males and females have adopted sex-related molecular strategies in response to solar UV-B radiation but also suggest many new insights, in particular into molecular regulation, via sex-biased gene expression. We conclude that these results can further enhance the sustainable exploitation and management of P. cathayana plants.

Proteomic analysis of salt-responsive proteins in the leaves of mangrove Kandelia candel during short-term stress

Salt stress is a major abiotic stress that limits crop productivity in many regions of the world. A comparative proteomic approach to identify salt stress-responsive proteins and to understand the molecular mechanisms was carried out in the woody halophyte Kandelia candel. Four-leaf-old K. candel seedlings were exposed to 150 (control), 300, 450, and 600 mM NaCl for 3 days. Proteins extracted from the leaves of K. candel seedlings were separated by two-dimensional gel electrophoresis (2-DE). More than 900 protein spots were detected on each gel, and 53 differentially expressed protein spots were located with at least two-fold differences in abundance on 2-DE maps, of which 48 were identified by matrix-assisted laser desorption ionization time-of-flight/time-of-flight mass spectrometry (MALDI-TOF-TOF/MS). The results showed that K. candel could withstand up to 450 mM NaCl stress by up-regulating proteins that are mainly involved in photosynthesis, respiration and energy metabolism, Na(+) compartmentalization, protein folding and assembly, and signal transduction. Physiological data, including superoxide dismutase (SOD) and dehydroascorbate reductase (DHAR) activities, hydrogen peroxide (H2O2) and superoxide anion radicals (O2(-)) contents, as well as Na(+) content and K(+)/Na(+) ratios all correlated well with our proteomic results. This study provides new global insights into woody halophyte salt stress responses. Identification of differentially expressed proteins promotes better understanding of the molecular basis for salt stress reduction in K. candel.

The poplar Phi class glutathione transferase: expression, activity and structure of GSTF1

Glutathione transferases (GSTs) constitute a superfamily of enzymes with essential roles in cellular detoxification and secondary metabolism in plants as in other organisms. Several plant GSTs, including those of the Phi class (GSTFs), require a conserved catalytic serine residue to perform glutathione (GSH)-conjugation reactions. Genomic analyses revealed that terrestrial plants have around ten GSTFs, eight in the Populus trichocarpa genome, but their physiological functions and substrates are mostly unknown. Transcript expression analyses showed a predominant expression of all genes both in reproductive (female flowers, fruits, floral buds) and vegetative organs (leaves, petioles). Here, we show that the recombinant poplar GSTF1 (PttGSTF1) possesses peroxidase activity toward cumene hydroperoxide and GSH-conjugation activity toward model substrates such as 2,4-dinitrochlorobenzene, benzyl and phenetyl isothiocyanate, 4-nitrophenyl butyrate and 4-hydroxy-2-nonenal but interestingly not on previously identified GSTF-class substrates. In accordance with analytical gel filtration data, crystal structure of PttGSTF1 showed a canonical dimeric organization with bound GSH or 2-(N-morpholino)ethanesulfonic acid molecules. The structure of these protein-substrate complexes allowed delineating the residues contributing to both the G and H sites that form the active site cavity. In sum, the presence of GSTF1 transcripts and proteins in most poplar organs especially those rich in secondary metabolites such as flowers and fruits, together with its GSH-conjugation activity and its documented stress-responsive expression suggest that its function is associated with the catalytic transformation of metabolites and/or peroxide removal rather than with ligandin properties as previously reported for other GSTFs.

Comparative studies focusing on transgenic through cp4EPSPS gene and non-transgenic soybean plants: an analysis of protein species and enzymes

This work evaluates the activity of a few key enzymes involved in combating reactive oxygen species (ROS), such as ascorbate peroxidase (EC 1.11.1.11), catalase (EC 1.11.1.6), glutathione reductase (EC 1.6.4.2), and superoxide dismutase (EC 1.15.1.1), as well as the concentration of malondialdehyde and hydrogen peroxide in transgenic and non-transgenic soybean leaves. Additionally, differential protein species from leaves of both genotypes were evaluated by applying a regulation factor of ≥1.8 to further corroborate the hypothesis that genetic modification itself can be a stress factor for these plants. For this task, transgenic soybean plants were obtained from seeds modified with the cp4EPSPS gene. The results revealed higher activities of all evaluated enzymes in transgenic than in non-transgenic soybean leaves (ranging from 13.8 to 70.1%), as well as higher concentrations of malondialdehyde and hydrogen peroxide in transgenic soybean leaves, clearly indicating a condition of oxidative stress established in the transgenic genotype. Additionally, 47 proteins were differentially abundant when comparing the leaves of both plants, with 26 species accurately identified, including the protein involved in the genetic modification (CP4EPSPS). From these results, it is possible to conclude that the plant is searching for a new equilibrium to maintain its metabolism because the stress condition is being maintained within levels that can be tolerated by the plant.

BIOLOGICAL SIGNIFICANCE

The present paper is the first one in the literature where are shown translational aspects involving plant stress and the genetic modification for soybean involving the cp4 EPSPS gene. The main biological importance of this work is to make possible the demystification of the genetic modification, allowing answers for some questions that still remain unknown, and enlarge our knowledge about genetically modified organisms. This article is part of a Special Issue entitled: Translational Plant Proteomics.

Comparative proteomic analysis of the hepatic response to heat stress in Muscovy and Pekin ducks: insight into thermal tolerance related to energy metabolism

The Pekin duck, bred from the mallard (Anas platyrhynchos) in china, is one of the most famous meat duck species in the world. However, it is more sensitive to heat stress than Muscovy duck, which is believed to have originated in South America. With temperature raising, mortality, laying performance, and meat quality of the Pekin duck are severely affected. This study aims to uncover the temperature-dependent proteins of two duck species using comparative proteomic approach. Duck was cultured under 39°C ± 0.5°C for 1 h, and then immediately returned to 20°C for a 3 h recovery period, the liver proteins were extracted and electrophoresed in two-dimensional mode. After analysis of gel images, 61 differentially expressed proteins were detected, 54 were clearly identified by MALDI TOF/TOF MS. Of the 54 differentially expressed protein spots identified, 7 were found in both species, whereas 47 were species specific (25 in Muscovy duck and 22 in Pekin duck). As is well known, chaperone proteins, such as heat shock protein (HSP) 70 and HSP10, were abundantly up-regulated in both species in response to heat stress. However, we also found that several proteins, such as α-enolase, and S-adenosylmethionine synthetase, showed different expression patterns in the 2 duck species. The enriched biological processes were grouped into 3 main categories according to gene ontology analysis: cell death and apoptosis (20.93%), amino acid metabolism (13.95%) and oxidation reduction (20.93%). The mRNA levels of several differentially expressed protein were investigated by real-time RT-PCR. To our knowledge, this study is the first to provide insights into the differential expression of proteins following heat stress in ducks and enables better understanding of possible heat stress response mechanisms in animals.

Sex-specific responses of Populus yunnanensis exposed to elevated CO2 and salinity

Populus yunnanensis Dode., a native dioecious woody plant in southwestern China, was employed as a model species to study sex-specific morphological, physiological and biochemical responses to elevated CO2 and salinity. To investigate the effects of elevated CO2 , salinity and their combination, the cuttings were exposed to two CO2 regimes (ambient CO2 and double ambient CO2 ) and two salt treatments in growth chambers. Males exhibited greater downregulation of net photosynthesis rate (Anet ) and carboxylation efficiency (CE) than females at elevated CO2 , whereas these sexual differences were lessened under salt stress. On the other hand, salinity induced a higher decrease in Anet and CE, more growth inhibition and leaf Cl(-) accumulation and more damage to cell organelles in females than in males, whereas the sexual differences in photosynthesis and growth were lessened at elevated CO2 . Moreover, elevated CO2 exacerbated membrane lipid peroxidation and organelle damage in females but not in males under salt stress. Our results indicated that: (1) females are more sensitive and suffer from greater negative effects than do males under salt stress, and elevated CO2 lessens the sexual differences in photosynthesis and growth under salt stress; (2) elevated CO2 tends to aggravate the negative effects of salinity in females; and (3) sex-specific reactions under the combination of elevated CO2 and salinity are distinct from single-stress responses. Therefore, these results provide evidence for different adaptive responses between plants of different sexes exposed to elevated CO2 and salinity.

Protein contribution to plant salinity response and tolerance acquisition

The review is focused on plant proteome response to salinity with respect to physiological aspects of plant salt stress response. The attention is paid to both osmotic and ionic effects of salinity stress on plants with respect to several protein functional groups. Therefore, the role of individual proteins involved in signalling, changes in gene expression, protein biosynthesis and degradation and the resulting changes in protein relative abundance in proteins involved in energy metabolism, redox metabolism, stressand defence-related proteins, osmolyte metabolism, phytohormone, lipid and secondary metabolism, mechanical stress-related proteins as well as protein posttranslational modifications are discussed. Differences between salt-sensitive (glycophytes) and salt-tolerant (halophytes) plants are analysed with respect to differential salinity tolerance. In conclusion, contribution of proteomic studies to understanding plant salinity tolerance is summarised and discussed.

Transcriptomic profiling of the salt-stress response in the wild recretohalophyte Reaumuria trigyna

Background

Reaumuria trigyna is an endangered small shrub endemic to desert regions in Inner Mongolia. This dicotyledonous recretohalophyte has unique morphological characteristics that allow it to tolerate the stress imposed by semi-desert saline soil. However, it is impossible to explore the mechanisms underlying this tolerance without detailed genomic information. Fortunately, newly developed high-throughput sequencing technologies are powerful tools for de novo sequencing to gain such information for this species.

Results

Two sequencing libraries prepared from control (C21) and NaCl-treated samples (T43) were sequenced using short reads sequencing technology (Illumina) to investigate changes in the R. trigyna transcriptome in response to salt stress. Among 65340 unigenes, 35495 (52.27%) were annotated with gene descriptions, conserved domains, gene ontology terms, and metabolic pathways with a cut-off E-value of 10^-5. These included 44 Gene Ontology (GO) terms, 119 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, and 25 Clusters of Orthologous Groups families. By comparing the transcriptomes from control and NaCl-treated plants, 5032 genes showed significantly differences in transcript abundance under salt stress (false discovery rate ≤ 0.001 and |log₂Ratio| ≥ 1). These genes were significantly enriched in 29 KEGG pathways and 26 GO terms. The transcription profiles indicated that genes related to ion transport and the reactive oxygen species scavenging system were relevant to the morphological and physiological characteristics of this species. The expression patterns of 30 randomly selected genes resulted from quantitative real-time PCR were basically consistent with their transcript abundance changes identified by RNA-seq.

Conclusions

The present study identified potential genes involved in salt tolerance of R. trigyna. The globally sequenced genes covered a considerable proportion of the R. trigyna transcriptome. These data represent a genetic resource for the discovery of genes related to salt tolerance in this species, and may be a useful source of reference sequences for closely related taxa. These results can also further our understanding of salt tolerance in other halophytes surviving under sodic stress.

Biochemical and proteomic analyses reveal that Populus cathayana males and females have different metabolic activities under chilling stress

Male and female poplars (Populus cathayana Rehd.) respond differently to environmental stresses. However, little is known about sex-dependent responses to chilling at the proteome level. To better understand these differences, a comparative proteomics investigation combined with a biochemical approach was used in the current study. Three-month-old poplar cuttings were treated at 25 or 4 °C for 14 days. Results revealed significant sexual differences in nitrogen metabolic enzymes and free amino acid components in response to chilling. The chilling-treated males showed higher activities of nitrate reductase and glutamine synthetase and higher contents of reduced glutathione, serine, arginine, leucine, glycine, proline and methionine than chilling-treated females. A total of 65 chilling-responsive spots were found, of which 48 showed significant sexual differences. These proteins are involved in photosynthesis, carbon and energy metabolism, metabolic processes of proteins, lipid metabolism, vitamin metabolism, stress defense, and gene expression regulation. The study shows that males have more effective metabolic processes and protective systems to chilling than females.

Mechanisms of plant salt response: insights from proteomics

Soil salinity is a major abiotic stress that limits plant growth and agriculture productivity. To cope with salt stress, plants have evolved complex salt-responsive signaling and metabolic processes at the cellular, organ, and whole-plant levels. Investigation of the physiological and molecular mechanisms underlying plant salinity tolerance will provide valuable information for effective engineering strategies. Current proteomics provides a high-throughput approach to study sophisticated molecular networks in plants. In this review, we describe a salt-responsive protein database by an integrated analysis of proteomics-based studies. The database contains 2171 salt-responsive protein identities representing 561 unique proteins. These proteins have been identified from leaves, roots, shoots, seedlings, unicells, grains, hypocotyls, radicles, and panicles from 34 plant species. The identified proteins provide invaluable information toward understanding the complex and fine-tuned plant salt-tolerance mechanisms in photosynthesis, reactive oxygen species (ROS) scavenging, ion homeostasis, osmotic modulation, signaling transduction, transcription, protein synthesis/turnover, cytoskeleton dynamics, and cross-tolerance to different stress conditions.