Rice proteomics: a model system for crop improvement and food security

Metabolomics-driven investigation of plant defense response against pest and pathogen attack

The advancement of metabolomics has assisted in the identification of various bewildering characteristics of the biological system. Metabolomics is a standard approach, facilitating crucial aspects of system biology with absolute quantification of metabolites using minimum samples, based on liquid/gas chromatography, mass spectrometry and nuclear magnetic resonance. The metabolome profiling has narrowed the wide gaps of missing information and has enhanced the understanding of a wide spectrum of plant-environment interactions by highlighting the complex pathways regulating biochemical reactions and cellular physiology under a particular set of conditions. This high throughput technique also plays a prominent role in combined analyses of plant metabolomics and other omics datasets. Plant metabolomics has opened a wide paradigm of opportunities for developing stress-tolerant plants, ensuring better food quality and quantity. However, despite advantageous methods and databases, the technique has a few limitations, such as ineffective 3D capturing of metabolites, low comprehensiveness, and lack of cell-based sampling. In the future, an expansion of plant-pathogen and plant-pest response towards the metabolite architecture is necessary to understand the intricacies of plant defence against invaders, elucidation of metabolic pathway operational during defence and developing a direct correlation between metabolites and biotic stresses. Our aim is to provide an overview of metabolomics and its utilities for the identification of biomarkers or key metabolites associated with biotic stress, devising improved diagnostic methods to efficiently assess pest and pathogen attack and generating improved crop varieties with the help of combined application of analytical and molecular tools.

Nutrient Elements Promote Disease Resistance in Tomato by Differentially Activating Immune Pathways

Nutrient elements play essential roles in plant growth, development, and reproduction. Balanced nutrition is critical for plant health and the ability to withstand biotic stress. Treatment with essential elements has been shown to induce disease resistance in certain cases. Understanding the functional mechanisms underlying plant immune responses to nutritional elements has the potential to provide new insights into crop improvement. In the present study, we investigated the effect of various elements-potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na)-in promoting resistance against the necrotrophic fungus Botrytis cinerea and the hemibiotrophic bacterium Xanthomonas euvesicatoria in tomato. We demonstrate that spray treatment of essential elements was sufficient to activate immune responses, inducing defense gene expression, cellular leakage, reactive oxygen species, and ethylene production. We report that different defense signaling pathways are required for induction of immunity in response to different elements. Our results suggest that genetic mechanisms that are modulated by nutrient elements can be exploited in agricultural practices to promote disease resistance.

Quantitative Proteomics at Early Stages of the Symbiotic Interaction Between Oryza sativa and Nostoc punctiforme Reveals Novel Proteins Involved in the Symbiotic Crosstalk

Symbiosis between cyanobacteria and plants is considered pivotal for biological nitrogen deposition in terrestrial ecosystems. Despite extensive knowledge of the ecology of plant-cyanobacterium symbioses, little is known about the molecular mechanisms involved in recognition between partners. Here, we conducted a quantitative sequential window acquisition of all theoretical fragment ion spectra mass spectrometry pipeline to analyze protein changes in Oryza sativa and Nostoc punctiforme during early events of symbiosis. We found differentially expressed proteins in both organisms linked to several biological functions, including signal transduction, adhesion, defense-related proteins and cell wall modification. In N. punctiforme we found increased expression of 62 proteins that have been previously described in other Nostoc-plant symbioses, reinforcing the robustness of our study. Our findings reveal new proteins activated in the early stages of the Nostoc-Oryza symbiosis that might be important for the recognition between the plant and the host. Oryza mutants in genes in the common symbiosis signaling pathway (CSSP) show reduced colonization efficiency, providing first insights on the involvement of the CSSP for the accommodation of N. punctiforme inside the plant cells. This information may have long-term implications for a greater understanding of the symbiotic interaction between Nostoc and land plants.

Integrated proteomics and metabolomics analysis of rice leaves in response to rice straw return

Straw return is crucial for the sustainable development of rice planting, but no consistent results were observed for the effect of straw return on rice growth. To investigate the response of rice leaves to rice straw return in Northeast China, two treatments were set, no straw return (S0) and rice straw return (SR). We analyzed the physiological index of rice leaves and measured differentially expressed proteins (DEPs) and differentially expressed metabolites (DEMs) levels in rice leaves by the use of proteomics and metabolomics approaches. The results showed that, compared with the S0 treatment, the SR treatment significantly decreased the dry weight of rice plants and non-structural carbohydrate contents and destroyed the chloroplast ultrastructure. In rice leaves of SR treatment, 329 DEPs were upregulated, 303 DEPs were downregulated, 44 DEMs were upregulated, and 71 DEMs were downregulated. These DEPs were mainly involved in photosynthesis and oxidative phosphorylation, and DEMs were mainly involved in alpha-linolenic acid metabolism, galactose metabolism, glycerophospholipid metabolism, pentose and gluconic acid metabolism, and other metabolic pathways. Rice straw return promoted the accumulation of scavenging substances of active oxygen and osmotic adjustment substances, such as glutathione, organic acids, amino acids, and other substances. The SR treatment reduced the photosynthetic capacity and energy production of carbon metabolism, inhibiting the growth of rice plants, while the increase of metabolites involved in defense against abiotic stress enhanced the adaptability of rice plants to straw return stress.

Ectopic Expression of the Rice Grain-Size-Affecting Gene GS5 in Maize Affects Kernel Size by Regulating Endosperm Starch Synthesis

Maize is one of the most important food crops, and maize kernel is one of the important components of maize yield. Studies have shown that the rice grain-size affecting gene GS5 increases the thousand-kernel weight by positively regulating the rice grain width and grain grouting rate. In this study, based on the GS5 transgenic maize obtained through transgenic technology with specific expression in the endosperm, molecular assays were performed on the transformed plants. Southern blotting results showed that the GS5 gene was integrated into the maize genome in a low copy number, and RT-PCR analysis showed that the exogenous GS5 gene was normally and highly expressed in maize. The agronomic traits of two successive generations showed that certain lines were significantly improved in yield-related traits, and the most significant changes were observed in the OE-34 line, where the kernel width increased significantly by 8.99% and 10.96%, the 100-kernel weight increased by 14.10% and 10.82%, and the ear weight increased by 13.96% and 15.71%, respectively; however, no significant differences were observed in the plant height, ear height, kernel length, kernel row number, or kernel number. In addition, the overexpression of the GS5 gene increased the grain grouting rate and affected starch synthesis in the rice grains. The kernels’ starch content in OE-25, OE-34, and OE-57 increased by 10.30%, 7.39%, and 6.39%, respectively. Scanning electron microscopy was performed to observe changes in the starch granule size, and the starch granule diameter of the transgenic line(s) was significantly reduced. RT-PCR was performed to detect the expression levels of related genes in starch synthesis, and the expression of these genes was generally upregulated. It was speculated that the exogenous GS5 gene changed the size of the starch granules by regulating the expression of related genes in the starch synthesis pathway, thus increasing the starch content. The trans-GS5 gene was able to be stably expressed in the hybrids with the genetic backgrounds of the four materials, with significant increases in the kernel width, 100-kernel weight, and ear weight. In this study, the maize kernel size was significantly increased through the endosperm-specific expression of the rice GS5 gene, and good material for the functional analysis of the GS5 gene was created, which was of great importance in theory and application.

Twenty years of rice genomics research: From sequencing and functional genomics to quantitative genomics

Since the completion of the rice genome sequencing project in 2005, we have entered the era of rice genomics, which is still in its ascendancy. Rice genomics studies can be classified into three stages: structural genomics, functional genomics, and quantitative genomics. Structural genomics refers primarily to genome sequencing for the construction of a complete map of rice genome sequence. This is fundamental for rice genetics and molecular biology research. Functional genomics aims to decode the functions of rice genes. Quantitative genomics is large-scale sequence- and statistics-based research to define the quantitative traits and genetic features of rice populations. Rice genomics has been a transformative influence on rice biological research and contributes significantly to rice breeding, making rice a good model plant for studying crop sciences.

Toward Integrated Multi-Omics Intervention: Rice Trait Improvement and Stress Management

Rice (Oryza sativa) is an imperative staple crop for nearly half of the world's population. Challenging environmental conditions encompassing abiotic and biotic stresses negatively impact the quality and yield of rice. To assure food supply for the unprecedented ever-growing world population, the improvement of rice as a crop is of utmost importance. In this era, "omics" techniques have been comprehensively utilized to decipher the regulatory mechanisms and cellular intricacies in rice. Advancements in omics technologies have provided a strong platform for the reliable exploration of genetic resources involved in rice trait development. Omics disciplines like genomics, transcriptomics, proteomics, and metabolomics have significantly contributed toward the achievement of desired improvements in rice under optimal and stressful environments. The present review recapitulates the basic and applied multi-omics technologies in providing new orchestration toward the improvement of rice desirable traits. The article also provides a catalog of current scenario of omics applications in comprehending this imperative crop in relation to yield enhancement and various environmental stresses. Further, the appropriate databases in the field of data science to analyze big data, and retrieve relevant information vis-à-vis rice trait improvement and stress management are described.

Improving drought tolerance in rice: Ensuring food security through multi-dimensional approaches

Drought has been highly prevalent around the world especially in Sub-Saharan Africa and South-East Asian countries. Consistent climatic instabilities and unpredictable rainfall patterns are further worsening the situation. Rice is a C₃ staple cereal and an important food crop for the majority of the world's population and drought stress is one of the major growth retarding threats for rice that slashes down grain quality and yield. Drought deteriorates rice productivity and induces various acclimation responses that aids in stress mitigation. However, the complexity of traits associated with drought tolerance has made the understanding of drought stress-induced responses in rice a challenging process. An integrative understanding based on physiological adaptations, omics, transgenic and molecular breeding approaches successively backed up to developing drought stress-tolerant rice. The review represents a step forward to develop drought-resilient rice plants by exploiting the knowledge that collaborates with omics-based developments with integrative efforts to ensure the compilation of all the possible strategies undertaken to develop drought stress-tolerant rice.

Proteomics and Metabolomics Studies on the Biotic Stress Responses of Rice: an Update

Biotic stresses represent a serious threat to rice production to meet global food demand and thus pose a major challenge for scientists, who need to understand the intricate defense mechanisms. Proteomics and metabolomics studies have found global changes in proteins and metabolites during defense responses of rice exposed to biotic stressors, and also reported the production of specific secondary metabolites (SMs) in some cultivars that may vary depending on the type of biotic stress and the time at which the stress is imposed. The most common changes were seen in photosynthesis which is modified differently by rice plants to conserve energy, disrupt food supply for biotic stress agent, and initiate defense mechanisms or by biotic stressors to facilitate invasion and acquire nutrients, depending on their feeding style. Studies also provide evidence for the correlation between reactive oxygen species (ROS) and photorespiration and photosynthesis which can broaden our understanding on the balance of ROS production and scavenging in rice-pathogen interaction. Variation in the generation of phytohormones is also a key response exploited by rice and pathogens for their own benefit. Proteomics and metabolomics studies in resistant and susceptible rice cultivars upon pathogen attack have helped to identify the proteins and metabolites related to specific defense mechanisms, where choosing of an appropriate method to identify characterized or novel proteins and metabolites is essential, considering the outcomes of host-pathogen interactions. Despites the limitation in identifying the whole repertoire of responsive metabolites, some studies have shed light on functions of resistant-specific SMs. Lastly, we illustrate the potent metabolites responsible for resistance to different biotic stressors to provide valuable targets for further investigation and application.

What Did We Learn From Plant Growth-Promoting Rhizobacteria (PGPR)-Grass Associations Studies Through Proteomic and Metabolomic Approaches?

Plant growth stimulation by microorganisms that interact in a mutually beneficial manner remains poorly understood. Understanding the nature of plant-bacteria interactions may open new routes for plant productivity enhancement, especially cereal crops consumed by humans. Proteomic and metabolomic analyses are particularly useful for elucidating these mechanisms. A complete depiction of these mechanisms will prompt researchers to develop more efficient plant-bacteria associations. The success of microorganisms as biofertilizers may replace the current massive use of chemical fertilizers, mitigating many environmental and economic issues. In this review, we discuss the recent advances and current state of the art in proteomics and metabolomics studies involving grass-bacteria associations. We also discuss essential subjects involved in the bacterial plant-growth promotion, such, nitrogen fixation, plant stress, defense responses, and siderophore production.

Proteomics of Rice-Magnaporthe oryzae Interaction: What Have We Learned So Far?

Rice blast disease, caused by Magnaporthe oryzae, is one of the major constraints to rice production, which feeds half of the world's population. Proteomic technologies have been used as effective tools in plant-pathogen interactions to study the biological pathways involved in pathogen infection, plant response, and disease progression. Advancements in mass spectrometry (MS) and apoplastic and plasma membrane protein isolation methods facilitated the identification and quantification of subcellular proteomes during plant-pathogen interaction. Proteomic studies conducted during rice-M. oryzae interaction have led to the identification of several proteins eminently involved in pathogen perception, signal transduction, and the adjustment of metabolism to prevent plant disease. Some of these proteins include receptor-like kinases (RLKs), mitogen-activated protein kinases (MAPKs), and proteins related to reactive oxygen species (ROS) signaling and scavenging, hormone signaling, photosynthesis, secondary metabolism, protein degradation, and other defense responses. Moreover, post-translational modifications (PTMs), such as phosphoproteomics and ubiquitin proteomics, during rice-M. oryzae interaction are also summarized in this review. In essence, proteomic studies carried out to date delineated the molecular mechanisms underlying rice-M. oryzae interactions and provided candidate proteins for the breeding of rice blast resistant cultivars.

Spatially Resolved Proteome Profiling of <200 Cells from Tomato Fruit Pericarp by Integrating Laser-Capture Microdissection with Nanodroplet Sample Preparation

Due to sensitivity limitations, global proteome measurements generally require large amounts of biological starting material, which masks heterogeneity within the samples and differential protein expression among constituent cell types. Methods for spatially resolved proteomics are being developed to resolve protein expression for distinct cell types among highly heterogeneous tissues, but have primarily been applied to mammalian systems. Here we evaluate the performance of cell-type-specific proteome analysis of tomato fruit pericarp tissues by a platform integrating laser-capture microdissection (LCM) and a recently developed automated sample preparation system (nanoPOTS, nanodroplet processing in one pot for trace samples). Tomato fruits were cryosectioned prior to LCM and tissues were dissected and captured directly into nanoPOTS chips for processing. Following processing, samples were analyzed by nanoLC-MS/MS. Approximately 1900 unique peptides and 422 proteins were identified on average from ∼0.04 mm² tissues comprising ∼8-15 parenchyma cells. Spatially resolved proteome analyses were performed using cells of outer epidermis, collenchyma, and parenchyma. Using ≤200 cells, a total of 1,870 protein groups were identified and the various tissues were easily resolved. The results provide spatial and tissue-specific insights into key enzymes and pathways involved in carbohydrate transport and source-sink relationships in tomato fruit. Of note, at the time of fruit ripening studied here, we identified differentially abundant proteins throughout the pericarp related to chlorophyll biogenesis, photosynthesis, and especially transport.

Rice Functional Genomics Research: Past Decade and Future

Rice (Oryza sativa) is a major staple food crop for more than 3.5 billion people worldwide. Understanding the regulatory mechanisms of complex agronomic traits in rice is critical for global food security. Rice is also a model plant for genomics research of monocotyledons. Thanks to the rapid development of functional genomic technologies, over 2000 genes controlling important agronomic traits have been cloned, and their molecular biological mechanisms have also been partially characterized. Here, we briefly review the advances in rice functional genomics research during the past 10 years, including a summary of functional genomics platforms, genes and molecular regulatory networks that regulate important agronomic traits, and newly developed tools for gene identification. These achievements made in functional genomics research will greatly facilitate the development of green super rice. We also discuss future challenges and prospects of rice functional genomics research.

High infestation levels of Schizotetranychus oryzae severely affects rice metabolism

High levels of Schizotetranychus oryzae phytophagous mite infestation on rice leaves can severely affect productivity. Physiological characterization showed that S. oryzae promotes a decrease in chlorophyll concentration and the establishment of a senescence process in rice leaves. Late-infested leaves also present high levels of superoxide radical and hydrogen peroxide accumulation, along with high levels of membrane integrity loss, which is indicative of cell death. To better understand the rice molecular responses to high levels of mite infestation, we employed the Multidimensional Protein Identification Technology (MudPIT) approach to identify differentially expressed proteins. We identified 83 and 88 proteins uniquely present in control and late-infested leaves, respectively, along with 11 and one proteins more abundant in control and late-infested leaves, respectively. S. oryzae infestation induces a decreased abundance of proteins related to translation, protease inhibition, and photosynthesis. On the other hand, infestation caused increased abundance of proteins involved in protein modification and degradation. Our results also suggest that S. oryzae infestation interferes with intracellular transport, DNA structure maintenance, and amino acid and lipid metabolism in rice leaves. Proteomic data were positively correlated with enzymatic assays and RT-qPCR analysis. Our findings describe the protein expression patterns of late-infested rice leaves and suggest several targets which could be tested in future biotechnological approaches aiming to avoid the population increase of phytophagous mite in rice plants.

Proteomics in commercial crops: An overview

Proteomics is a rapidly growing area of biological research that is positively affecting plant science. Recent advances in proteomic technology, such as mass spectrometry, can now identify a broad range of proteins and monitor their modulation during plant growth and development, as well as during responses to abiotic and biotic stresses. In this review, we highlight recent proteomic studies of commercial crops and discuss the advances in understanding of the proteomes of these crops. We anticipate that proteomic-based research will continue to expand and contribute to crop improvement.

SIGNIFICANCE

Plant proteomics study is a rapidly growing area of biological research that is positively impacting plant science. With the recent advances in new technologies, proteomics not only allows us to comprehensively analyses crop proteins, but also help us to understand the functions of the genes. In this review, we highlighted recent proteomic studies in commercial crops and updated the advances in our understanding of the proteomes of these crops. We believe that proteomic-based research will continue to grow and contribute to the improvement of crops.

Cereal Crop Proteomics: Systemic Analysis of Crop Drought Stress Responses Towards Marker-Assisted Selection Breeding

Sustainable crop production is the major challenge in the current global climate change scenario. Drought stress is one of the most critical abiotic factors which negatively impact crop productivity. In recent years, knowledge about molecular regulation has been generated to understand drought stress responses. For example, information obtained by transcriptome analysis has enhanced our knowledge and facilitated the identification of candidate genes which can be utilized for plant breeding. On the other hand, it becomes more and more evident that the translational and post-translational machinery plays a major role in stress adaptation, especially for immediate molecular processes during stress adaptation. Therefore, it is essential to measure protein levels and post-translational protein modifications to reveal information about stress inducible signal perception and transduction, translational activity and induced protein levels. This information cannot be revealed by genomic or transcriptomic analysis. Eventually, these processes will provide more direct insight into stress perception then genetic markers and might build a complementary basis for future marker-assisted selection of drought resistance. In this review, we survey the role of proteomic studies to illustrate their applications in crop stress adaptation analysis with respect to productivity. Cereal crops such as wheat, rice, maize, barley, sorghum and pearl millet are discussed in detail. We provide a comprehensive and comparative overview of all detected protein changes involved in drought stress in these crops and have summarized existing knowledge into a proposed scheme of drought response. Based on a recent proteome study of pearl millet under drought stress we compare our findings with wheat proteomes and another recent study which defined genetic marker in pearl millet.

Fungal Elicitor MoHrip2 Induces Disease Resistance in Rice Leaves, Triggering Stress-Related Pathways

MoHrip2 Magnaporthe oryzae hypersensitive protein 2 is an elicitor protein of rice blast fungus M. oryzae. Rice seedlings treated with MoHrip2 have shown an induced resistance to rice blast. To elucidate the mechanism underlying this MoHrip2 elicitation in rice, we used differential-display 2-D gel electrophoresis and qRT-PCR to assess the differential expression among the total proteins extracted from rice leaves at 24 h after treatment with MoHrip2 and buffer as a control. Among ~1000 protein spots detected on each gel, 10 proteins were newly induced, 4 were up-regulated, and 3 were down-regulated in MoHrip2-treated samples compared with the buffer control. Seventeen differentially expressed proteins were detected using MS/MS analysis and categorized into six groups according to their putative function: defense-related transcriptional factors, signal transduction-related proteins, reactive oxygen species (ROS) production, programmed cell death (PCD), defense-related proteins, and photosynthesis and energy-related proteins. The qPCR results (relative expression level of genes) further supported the differential expression of proteins in MoHrip2-treated rice leaves identified with 2D-gel, suggesting that MoHrip2 triggers an early defense response in rice leaves via stress-related pathways, and the results provide evidence for elicitor-induced resistance at the protein level.

Ascribing Functions to Genes: Journey Towards Genetic Improvement of Rice Via Functional Genomics

Rice, one of the most important cereal crops for mankind, feeds more than half the world population. Rice has been heralded as a model cereal owing to its small genome size, amenability to easy transformation, high synteny to other cereal crops and availability of complete genome sequence. Moreover, sequence wealth in rice is getting more refined and precise due to resequencing efforts. This humungous resource of sequence data has confronted research fraternity with a herculean challenge as well as an excellent opportunity to functionally validate expressed as well as regulatory portions of the genome. This will not only help us in understanding the genetic basis of plant architecture and physiology but would also steer us towards developing improved cultivars. No single technique can achieve such a mammoth task. Functional genomics through its diverse tools viz. loss and gain of function mutants, multifarious omics strategies like transcriptomics, proteomics, metabolomics and phenomics provide us with the necessary handle. A paradigm shift in technological advances in functional genomics strategies has been instrumental in generating considerable amount of information w.r.t functionality of rice genome. We now have several databases and online resources for functionally validated genes but despite that we are far from reaching the desired milestone of functionally characterizing each and every rice gene. There is an urgent need for a common platform, for information already available in rice, and collaborative efforts between researchers in a concerted manner as well as healthy public-private partnership, for genetic improvement of rice crop better able to handle the pressures of climate change and exponentially increasing population.

Proteomic Responses of Switchgrass and Prairie Cordgrass to Senescence

Senescence in biofuel grasses is a critical issue because early senescence decreases potential biomass production by limiting aerial growth and development. 2-Dimensional, differential in-gel electrophoresis (2D-DIGE) followed by mass spectrometry of selected protein spots was used to evaluate differences between leaf proteomes of early (ES)- and late- senescing (LS) genotypes of Prairie cordgrass (ES/LS PCG) and switchgrass (ES/LS SG), just before and after senescence was initiated. Analysis of the manually filtered and statistically evaluated data indicated that 69 proteins were significantly differentially abundant across all comparisons, and a majority (41%) were associated with photosynthetic processes as determined by gene ontology analysis. Ten proteins were found in common between PCG and SG, and nine and 18 proteins were unique to PCG and SG respectively. Five of the 10 differentially abundant spots common to both species were increased in abundance, and five were decreased in abundance. Leaf proteomes of the LS genotypes of both grasses analyzed before senescence contained significantly higher abundances of a 14-3-3 like protein and a glutathione-S-transferase protein when compared to the ES genotypes, suggesting differential cellular metabolism in the LS vs. the ES genotypes. The higher abundance of 14-3-3 like proteins may be one factor that impacts the senescence process in both LS PCG and LS SG. Aconitase dehydratase was found in greater abundance in all four genotypes after the onset of senescence, consistent with literature reports from genetic and transcriptomic studies. A Rab protein of the Ras family of G proteins and an s-adenosylmethionine synthase were more abundant in ES PCG when compared with the LS PCG. In contrast, several proteins associated with photosynthesis and carbon assimilation were detected in greater abundance in LS PCG when compared to ES PCG, suggesting that a loss of these proteins potentially contributed to the ES phenotype in PCG. Overall, this study provides important data that can be utilized toward delaying senescence in both PCG and SG, and sets a foundational base for future improvement of perennial grass germplasm for greater aerial biomass productivity.

Leaf Proteome Analysis Reveals Prospective Drought and Heat Stress Response Mechanisms in Soybean

Drought and heat are among the major abiotic stresses that affect soybean crops worldwide. During the current investigation, the effect of drought, heat, and drought plus heat stresses was compared in the leaves of two soybean varieties, Surge and Davison, combining 2D-DIGE proteomic data with physiology and biochemical analyses. We demonstrated how 25 differentially expressed photosynthesis-related proteins affect RuBisCO regulation, electron transport, Calvin cycle, and carbon fixation during drought and heat stress. We also observed higher abundance of heat stress-induced EF-Tu protein in Surge. It is possible that EF-Tu might have activated heat tolerance mechanisms in the soybean. Higher level expressions of heat shock-related protein seem to be regulating the heat tolerance mechanisms. This study identifies the differential expression of various abiotic stress-responsive proteins that regulate various molecular processes and signaling cascades. One inevitable outcome from the biochemical and proteomics assays of this study is that increase of ROS levels during drought stress does not show significant changes at the phenotypic level in Davison and this seems to be due to a higher amount of carbonic anhydrase accumulation in the cell which aids the cell to become more resistant to cytotoxic concentrations of H2O2.

A year (2014-2015) of plants in Proteomics journal. Progress in wet and dry methodologies, moving from protein catalogs, and the view of classic plant biochemists

The present review is an update of the previous one published in Proteomics 2015 Reviews special issue [Jorrin-Novo, J. V. et al., Proteomics 2015, 15, 1089-1112] covering the July 2014-2015 period. It has been written on the bases of the publications that appeared in Proteomics journal during that period and the most relevant ones that have been published in other high-impact journals. Methodological advances and the contribution of the field to the knowledge of plant biology processes and its translation to agroforestry and environmental sectors will be discussed. This review has been organized in four blocks, with a starting general introduction (literature survey) followed by sections focusing on the methodology (in vitro, in vivo, wet, and dry), proteomics integration with other approaches (systems biology and proteogenomics), biological information, and knowledge (cell communication, receptors, and signaling), ending with a brief mention of some other biological and translational topics to which proteomics has made some contribution.

Effect of salt stress on ion concentration, proline content, antioxidant enzyme activities and gene expression in tomato cultivars

Salinity is a constraint limiting plant growth and productivity of crops throughout the world. Understanding the mechanism underlying plant response to salinity provides new insights into the improvement of salt tolerance-crops of importance. In the present study, we report on the responses of twenty cultivars of tomato. We have clustered genotypes into scale classes according to their response to increased NaCl levels. Three local tomato genotypes, representative of different saline scale classes, were selected for further investigation. During early (0 h, 6 h and 12 h) and later (7 days) stages of the response to salt treatment, ion concentrations (Na⁺, K⁺ and Ca²⁺), proline content, enzyme activities (catalase, ascorbate peroxidase and guiacol peroxidase) were recorded. qPCR analysis of candidate genes WRKY (8, 31and 39), ERF (9, 16 and 80), LeNHX (1, 3 and 4) and HKT (class I) were performed. A high K⁺, Ca^2 +and proline accumulation as well as a decrease of Na⁺ concentration-mediated salt tolerance. Concomitant with a pattern of high-antioxidant enzyme activities, tolerant genotypes also displayed differential patterns of gene expression during the response to salt stress.

iTRAQ-based quantitative proteomics analysis of rice leaves infected by Rice stripe virus reveals several proteins involved in symptom formation

Background

Rice plants infected by Rice stripe virus (RSV) usually leads to chlorosis and death of newly emerged leaves. However, the mechanism of RSV-induced these symptoms was not clear.

Methods

We used an iTRAQ approach for a quantitative proteomics comparison of non-infected and infected rice leaves. RT-qPCR and Northern blot analyses were performed for assessing the transcription of candidate genes.

Results

As a whole, 681 (65.8 % downregulated, 34.2 % upregulated infected vs. non-infected) differentially accumulated proteins were identified. A bioinformatics analysis indicated that ten of these regulated proteins are involved in chlorophyll biosynthesis and three in cell death processes. Subsequent RT-qPCR results showed that downregulation of magnesium chelatase was due to reduced expression levels of the genes encoding subunits CHLI and CHLD, which resulted in chlorophyll reduction involved in leaf chlorosis. Three aspartic proteases expressed higher in RSV-infected leaves than those in the control leaves, which were also implicated in RSV-induced cell death. Northern blot analyses of CHLI and p0026h03.19 confirmed the RT-qPCR results.

Conclusions

The magnesium chelatase and aspartic proteases may be associated with RSV-induced leaf chlorosis and cell death, respectively. The findings may yield new insights into mechanisms underlying rice stripe disease symptom formation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-015-0328-y) contains supplementary material, which is available to authorized users.

Getting the 'MOST' out of crop improvement

Unraveling the function of genes affecting agronomic traits is accelerating due to progress in DNA sequencing and other high-throughput genomic approaches. Characterized genes can be exploited by plant breeders by using either marker-aided selection (MAS) or transgenic procedures. Here, we propose a third 'outlet', 'molecular strengthening' (MOST), as alternative option for exploiting detailed molecular understanding of trait expression, which is comparable to the pharmaceutical treatment of human diseases. MOST treatments can be used to enhance yield stability. Alternatively, they can be used to control traits temporally, such as flowering time to facilitate crosses for plant breeders. We also discuss the essence for developing MOST treatments, their prospects, and limitations.

Identification and analysis of the mechanism underlying heat-inducible expression of rice aconitase 1

Respiratory metabolism is an important though poorly understood facet of plant adaptation to stress. Posttranslational modification of aconitase, a component of the tricarboxylic acid cycle (TCA), may be involved in stress tolerance. However, such stress-related transcriptional regulation and its mechanism remain unknown. In this study, we found that expression of the rice Aconitase gene OsACO1 is induced in a time-dependent manner by heat but not other typical abiotic stresses. To analyze the transcriptional regulation mechanism underlying the response to heat, the OsACO1 promoter (POsACO1) was isolated and characterized in transgenic rice. Using qualitative and quantitative analyses, we found that the expression of the GUS reporter gene responded to heat in different tissues and at different stages of development when driven by POsACO1. A series of 5' distal deletions of POsACO1 was generated to delineate the region responsible for heat-induced gene expression. Transient expression analyses in tobacco leaves identified a 322-bp minimal region between -1386 and -1065 as being essential and sufficient for heat-induced expression by POsACO1. We screened for known heat response-related cis-elements in this 322-bp region; however, sequences correlating with heat-induced gene expression were not identified in POsACO1. Therefore, truncations and successive mutagenesis analyses were performed in this 322-bp region. By comparing the activities of promoter fragments and their derivatives, our results indicated that the heat response element resided in a 9-bp region between -1132 and -1124, a sequence that contains a W-box motif. Additional site-directed mutagenesis analyses eliminated the heat response activity of POsACO1 via the W-box element, and an electrophoretic mobility shift assay (EMSA) indicated the binding of POsACO1 by factors in the nuclear extracts of heat-stressed rice seedlings in a W-box-dependent manner. Our results illustrate the expression pattern of a key component of the TCA response to abiotic stress and establish a putative regulatory pathway in the transcriptional modulation of rice respiratory metabolism genes in response to heat.

Genetic diversity in tef [Eragrostis tef (Zucc.) Trotter]

Tef [Eragrostis tef (Zucc.) Trotter] is a cereal crop resilient to adverse climatic and soil conditions, and possessing desirable storage properties. Although tef provides high quality food and grows under marginal conditions unsuitable for other cereals, it is considered to be an orphan crop because it has benefited little from genetic improvement. Hence, unlike other cereals such as maize and wheat, the productivity of tef is extremely low. In spite of the low productivity, tef is widely cultivated by over six million small-scale farmers in Ethiopia where it is annually grown on more than three million hectares of land, accounting for over 30% of the total cereal acreage. Tef, a tetraploid with 40 chromosomes (2n = 4x = 40), belongs to the family Poaceae and, together with finger millet (Eleusine coracana Gaerth.), to the subfamily Chloridoideae. It was originated and domesticated in Ethiopia. There are about 350 Eragrostis species of which E. tef is the only species cultivated for human consumption. At the present time, the gene bank in Ethiopia holds over five thousand tef accessions collected from geographical regions diverse in terms of climate and elevation. These germplasm accessions appear to have huge variability with regard to key agronomic and nutritional traits. In order to properly utilize the variability in developing new tef cultivars, various techniques have been implemented to catalog the extent and unravel the patterns of genetic diversity. In this review, we show some recent initiatives investigating the diversity of tef using genomics, transcriptomics and proteomics and discuss the prospect of these efforts in providing molecular resources that can aid modern tef breeding.

Fourteen years of plant proteomics reflected in Proteomics: moving from model species and 2DE-based approaches to orphan species and gel-free platforms

In this article, the topic of plant proteomics is reviewed based on related papers published in the journal Proteomics since publication of the first issue in 2001. In total, around 300 original papers and 41 reviews published in Proteomics between 2000 and 2014 have been surveyed. Our main objective for this review is to help bridge the gap between plant biologists and proteomics technologists, two often very separate groups. Over the past years a number of reviews on plant proteomics have been published . To avoid repetition we have focused on more recent literature published after 2010, and have chosen to rather make continuous reference to older publications. The use of the latest proteomics techniques and their integration with other approaches in the "systems biology" direction are discussed more in detail. Finally we comment on the recent history, state of the art, and future directions of plant proteomics, using publications in Proteomics to illustrate the progress in the field. The review is organized into two major blocks, the first devoted to provide an overview of experimental systems (plants, plant organs, biological processes) and the second one to the methodology.

Advances in plant proteomics toward improvement of crop productivity and stress resistancex

Abiotic and biotic stresses constrain plant growth and development negatively impacting crop production. Plants have developed stress-specific adaptations as well as simultaneous responses to a combination of various abiotic stresses with pathogen infection. The efficiency of stress-induced adaptive responses is dependent on activation of molecular signaling pathways and intracellular networks by modulating expression, or abundance, and/or post-translational modification (PTM) of proteins primarily associated with defense mechanisms. In this review, we summarize and evaluate the contribution of proteomic studies to our understanding of stress response mechanisms in different plant organs and tissues. Advanced quantitative proteomic techniques have improved the coverage of total proteomes and sub-proteomes from small amounts of starting material, and characterized PTMs as well as protein-protein interactions at the cellular level, providing detailed information on organ- and tissue-specific regulatory mechanisms responding to a variety of individual stresses or stress combinations during plant life cycle. In particular, we address the tissue-specific signaling networks localized to various organelles that participate in stress-related physiological plasticity and adaptive mechanisms, such as photosynthetic efficiency, symbiotic nitrogen fixation, plant growth, tolerance and common responses to environmental stresses. We also provide an update on the progress of proteomics with major crop species and discuss the current challenges and limitations inherent to proteomics techniques and data interpretation for non-model organisms. Future directions in proteomics research toward crop improvement are further discussed.

Phosphoproteomics in cereals

Cereals are the most important crop plant supplying staple food throughout the world. The economic importance and continued breeding of crop plants such as rice, maize, wheat, or barley require a detailed scientific understanding of adaptive and developmental processes. Protein phosphorylation is one of the most important regulatory posttranslational modifications and its analysis allows deriving functional and regulatory principles in plants. This minireview summarizes the current knowledge of phosphoproteomic studies in cereals.

Model plant systems in salinity and drought stress proteomics studies: a perspective on Arabidopsis and Sorghum

More than a decade after the sequencing of its genome, Arabidopsis still stands as the epitome of a model system in plant biology. Arabidopsis proteomics has also taught us great lessons on different aspects of plant growth, development and physiology. Without doubt our understanding of basic principles of plant biology would not have been this advanced if it were not for knowledge gained using Arabidopsis as a model system. However, with the projections of global climate change and rapid population growth, it is high time we evaluate the applicability of this model system in studies aimed at understanding abiotic stress tolerance and adaptation, with a particular emphasis on maintaining yield under hot and dry environmental conditions. Because of the innate nature of sorghum's tolerance to drought and moderate tolerance to salinity stresses, we believe sorghum is the next logical model system in such studies amongst cereals. In this acute view, we highlight the importance of Arabidopsis as a model system, briefly discuss its potential limitations in drought and salt stress studies, and present our views on the potential usefulness of sorghum as a model system for cereals in drought and salinity stress proteomic studies.

Mechanism of salinity tolerance in plants: physiological, biochemical, and molecular characterization

Salinity is a major abiotic stress limiting growth and productivity of plants in many areas of the world due to increasing use of poor quality of water for irrigation and soil salinization. Plant adaptation or tolerance to salinity stress involves complex physiological traits, metabolic pathways, and molecular or gene networks. A comprehensive understanding on how plants respond to salinity stress at different levels and an integrated approach of combining molecular tools with physiological and biochemical techniques are imperative for the development of salt-tolerant varieties of plants in salt-affected areas. Recent research has identified various adaptive responses to salinity stress at molecular, cellular, metabolic, and physiological levels, although mechanisms underlying salinity tolerance are far from being completely understood. This paper provides a comprehensive review of major research advances on biochemical, physiological, and molecular mechanisms regulating plant adaptation and tolerance to salinity stress.