The proteome of exudates from germinatingLupinus albusseeds is secreted through a selective dual-step process and contains proteins involved in plant defence

Transcriptome-based analysis of candidate gene markers associated with resistance mechanism to Phytophthora melonis that causes root and crown rot in pumpkin

Root and crown rot incited by an oomycete, Phytophthora melonis , causes significant yield losses in commercial pumpkin (Cucurbita pepo ) production worldwide. Currently, resistant cultivars and knowledge of molecular mechanism of C. pepo against P. melonis are scarce. Here, we analysed the quantitative gene expression changes of 10 candidate gene markers (bHLH87, ERF014, HSF, MYB, PR-1, WRKY21, CPI, POD, PSK, SGT ) in pumpkin roots and leaves at three time points (h post-inoculation, hpi) following inoculation with P. melonis in two resistant (Ghelyani and Tanbal), and two susceptible (Marmari and Khoreshti) varieties of pumpkin. Gene expression using quantitative real time PCR along a time course revealed the strongest transcriptomic response at 48 and 72hpi in resistant genotypes, 1.1-2.7-fold in roots and leaves, respectively, with a high significant correlation (r =0.857**-0.974**). We also found that CPI , PSK, SGT1 and POD act as a dual regulator that similarly modulate immunity not only against P. melonis , but also against other diseases such as early blight (Alternaria cucumerina) , powdery mildew (Podosphaera xanthii ), downy mildews (Pseudoperonospora cubensis ), and pathogenic plant nematodes (Meloidogyne javanica ). Furthermore, significantly higher activities of the ROS scavenging defence enzymes, catalase (1.6-fold increase) and peroxidase (6-fold increase) were observed in the roots of resistant cultivars at different hpi compared with non-inoculated controls. In addition, the biomass growth parameters including leaf and root length, stem and root diameter, root fresh weight and volume were significantly different among studied genotypes. Cumulatively, the transcriptome data provide novel insights into the response of pumpkins for improving pumpkin breeding to P. melonis .

Antifungal Activity and Biochemical Profiling of Exudates from Germinating Maize Nostrano di Storo Local Variety

Plant pathogens are responsible for important damages to valuable crops causing important economic losses. Agrobiodiversity protection is crucial for the valorization of local varieties that could possess higher resistance to biotic and abiotic stress. At the beginning of germination, seeds are susceptible to pathogens attacks, thus they can release endogenous antimicrobial compounds of different natures in the spermosphere, to contrast proliferation of microorganisms. The work aimed at characterizing the maize of local variety Nostrano di Storo seed exudates secreted during the first phases of germination, to identify compounds active in the defense towards pathogens. Storo seed exudates were proven to inhibit F. verticilloides germination. In order to investigate the cause of the described effect, compositional profiling of the exudates was performed through NMR, lipidomic, and proteomic analyses. This study suggests an important role of microbial endophytic communities in the protection of the seed during the early phases of the germination process and their interplay with fatty acids released by the seeds, rather than a specific antifungal compound. The valorization of agronomically acceptable maize lines with pre-harvest enhanced resistances to pathogens contamination could lead, in the near future, to commercially available varieties potentially requiring more limited chemical protective treatments.

Thermal Shift Assay as a Tool to Evaluate the Release of Breakdown Peptides from Cowpea β-Vignin during Seed Germination

The present work aimed to characterize the molecular relationships between structure and function of the seed storage protein β-vignin, the vicilin storage protein of cowpea (Vigna unguiculata, l. Walp) seeds. The molecular characterization of β-vignin was carried out firstly by assessing its thermal stability, under different conditions of pH and ionic strength, by thermal shift assay (TSA) using SYPRO Orange fluorescent dye. Secondly, its aggregation propensity was evaluated using a combination of chromatographic and electrophoretic techniques. Two forms of β-vignin were considered: the native form purified from mature quiescent seeds, and a stable breakdown intermediate of 27 kDa produced while seeds germinate. TSA is a useful tool for determining and following over time the structural changes that occur to the protein during germination. The main result was the molecular characterization of the 27 kDa intermediate breakdown polypeptide, which, to the best of our knowledge, has never been described before. β-vignin seems to retain its trimeric conformation despite the evident degradation of its polypeptides.

In vitro assessment of the efficacy of protein exudates from seeds against Haemonchus contortus

Nematodes develop resistance to the most common commercially available drugs. The aim of this study was to identify and evaluate the action of protein exudates from Mimosa caesalpiniifolia, Leucaena leucocephala, Acacia mangium, and Stylosanthes capitata seeds on the gastrointestinal nematode Haemonchus contortus. The exuded proteins were precipitated, dialyzed, lyophilized, and assessed for their effect on egg hatching and artificial larval exsheathment inhibition. Proteome analysis of the protein extracts was also performed. Although no egg-hatching inhibition was observed, all exudates showed efficacy in inhibiting the larval exsheathment of H. contortus larvae with an EC₅₀ varying from 0.61 to 0.26 mg P mL^-1. Proteomic analysis revealed the presence of proteases, protease inhibitors, chitinases, and lectins among other proteins in the exudates. Most of the exuded proteins belong to the oxidative stress/plant defense and energy/carbohydrate metabolism functional clusters. This study concluded that the bioactive proteins from different classes exuded by seeds of M. caesalpiniifolia, L. leucocephala, A. mangium, and S. capitata show stage-specific inhibition against H. contortus.

Inhibition of Protease and Egg Hatching of Haemonchus contortus by Soybean Seed Exudates

Gastrointestinal nematode infection of small ruminants causes losses in livestock production. Plant compounds show promises as alternatives to commercial anthelmintics that have been exerting selective pressures that lead to the development of drug-resistant parasites. Soybean (Glycine max) is an economical value crop, with a higher protein content compared to other legumes. The objective of this study was to evaluate whether the protease inhibitors exuded from the G. max mature seeds have anthelmintic activity against Haemonchus contortus. To obtain the soybean exudates (SEX), mature seeds were immersed in 100 mM sodium acetate buffer, pH 5.0, at 10 C, for 24 hr. Then the naturally released substances present in SEX were collected and exhaustively dialyzed (cutoff 12 kDa) against distilled water. The dialyzed seed exudates (SEXD) were heated at 100 C for 10 min and centrifuged (12,000 g, at 4 C for 15 min). The supernatant obtained was recovered and designated as the heat-treated exudate fraction (SEXDH). The protein content, protease inhibitor activity, and the effect of each fraction on H. contortus egg hatch rate were evaluated. The inhibition extent of SEX, SEXD, and SEXDH on H. contortus egg proteases was 31.1, 42.9, and 63.8%, respectively. Moreover, SEX, SEXD, and SEXDH inhibited the egg hatching with EC50 of 0.175, 0.175, and 0.241 mg ml-1, respectively. Among the commercial protease inhibitors tested, only EDTA and E-64 inhibited the H. contortus hatch rate (79.0 and 28.9%, respectively). We present evidence demonstrating that soybean exudate proteins can effectively inhibit H. contortus egg hatching. This bioactivity is displayed by thermostable proteins and provides evidence that protease inhibitors are a potential candidate for anthelmintic use.

Breeding, Genetics, and Genomics Approaches for Improving Fusarium Wilt Resistance in Major Grain Legumes

Fusarium wilt (FW) disease is the key constraint to grain legume production worldwide. The projected climate change is likely to exacerbate the current scenario. Of the various plant protection measures, genetic improvement of the disease resistance of crop cultivars remains the most economic, straightforward and environmental-friendly option to mitigate the risk. We begin with a brief recap of the classical genetic efforts that provided first insights into the genetic determinants controlling plant response to different races of FW pathogen in grain legumes. Subsequent technological breakthroughs like sequencing technologies have enhanced our understanding of the genetic basis of both plant resistance and pathogenicity. We present noteworthy examples of targeted improvement of plant resistance using genomics-assisted approaches. In parallel, modern functional genomic tools like RNA-seq are playing a greater role in illuminating the various aspects of plant-pathogen interaction. Further, proteomics and metabolomics have also been leveraged in recent years to reveal molecular players and various signaling pathways and complex networks participating in host-pathogen interaction. Finally, we present a perspective on the challenges and limitations of high-throughput phenotyping and emerging breeding approaches to expeditiously develop FW-resistant cultivars under the changing climate.

Characterization of Chenopodin Isoforms from Quinoa Seeds and Assessment of Their Potential Anti-Inflammatory Activity in Caco-2 Cells

Several food-derived molecules, including proteins and peptides, can show bioactivities toward the promotion of well-being and disease prevention in humans. There is still a lack of information about the potential effects on immune and inflammatory responses in mammalian cells following the ingestion of seed storage proteins. This study, for the first time, describes the potential immunomodulation capacity of chenopodin, the major protein component of quinoa seeds. After characterizing the molecular features of the purified protein, we were able to separate two different forms of chenopodin, indicated as LcC (Low charge Chenopodin, 30% of total chenopodin) and HcC (High charge Chenopodin, 70% of total chenopodin). The biological effects of LcC and HcC were investigated by measuring NF-κB activation and IL-8 expression studies in undifferentiated Caco-2 cells. Inflammation was elicited using IL-1β. The results indicate that LcC and HcC show potential anti-inflammatory activities in an intestinal cell model, and that the proteins can act differently, depending on their structural features. Furthermore, the molecular mechanisms of action and the structural/functional relationships of the protein at the basis of the observed bioactivity were investigated using in silico analyses and structural predictions.

Legumes Protease Inhibitors as Biopesticides and Their Defense Mechanisms against Biotic Factors

Legumes are affected by biotic factors such as insects, molds, bacteria, and viruses. These plants can produce many different molecules in response to the attack of phytopathogens. Protease inhibitors (PIs) are proteins produced by legumes that inhibit the protease activity of phytopathogens. PIs are known to reduce nutrient availability, which diminishes pathogen growth and can lead to the death of the pathogen. PIs are classified according to the specificity of the mechanistic activity of the proteolytic enzymes, with serine and cysteine protease inhibitors being studied the most. Previous investigations have reported the efficacy of these highly stable proteins against diverse biotic factors and the concomitant protective effects in crops, representing a possible replacement of toxic agrochemicals that harm the environment.

Gene expression during development and overexpression after Cercospora kikuchii and salicylic acid challenging indicate defensive roles of the soybean toxin

KEY MESSAGE

SBTX has defensive role against C. kikuchii, and therefore, its constituent genes SBTX17 and SBTX27 are promising candidates to engineer pathogen resistant plants. Soybean (Glycine max [L.] Merr.) is economically the most important legume crop in the world. Its productivity is strongly affected by fungal diseases, which reduce soybean production and seed quality and cause losses of billions of dollars worldwide. SBTX is a protein that apparently takes part in the defensive chemical arsenal of soybean against pathogens. This current study provides data that reinforce this hypothesis. Indeed, SBTX inhibited in vitro the mycelial growth of Cercospora kikuchii, it is constitutively located in the epidermal region of the soybean seed cotyledons, and it is exuded from mature imbibed seeds. Moreover, RT-qPCR analysis of the SBTX associated genes, SBTX17 and SBTX27, which encode for the 17 and 27 kDa polypeptide chains, showed that both genes are expressed in all studied plant tissues during the soybean development, with the highest levels found in the mature seeds and unifoliate leaves. In addition, to assess a local response of the soybean secondary leaves from 35-day-old plants, they were inoculated with C. kikuchii and treated with salicylic acid. It was verified using RT-qPCR that SBTX17 and SBTX27 genes overexpressed in leaves compared to controls. These findings strongly suggest that SBTX has defensive roles against C. kikuchii. Therefore, SBTX17 and SBTX27 genes are promising candidates to engineer pathogen resistant plants.

Myracrodruon urundeuva seed exudates proteome and anthelmintic activity against Haemonchus contortus

Seed exudates are plant-derived natural bioactive compounds consisting of a complex mixture of organic and inorganic molecules. Plant seed exudates have been poorly studied against parasite nematodes. This study was undertaken to identify proteins in the Myracrodruon urundeuva seed exudates and to assess the anthelmintic activity against Haemonchus contortus, an important parasite of small ruminants. M. urundeuva seed exudates (SEX) was obtained after immersion of seeds in sodium acetate buffer. SEX was fractionated with ammonium sulfate at 0–90% concentration to generate the ressuspended pellet (SEXF1) and the supernatant (SEXF2). SEX, SEXF1, and SEXF2 were exhaustively dialyzed against distilled water (cut-off: 12 kDa) and the protein contents determined. Mass spectrometry analyses of SEX, SEXF1, and SEXF2 were done to identify proteins and secondary metabolites. The seed exudates contained protease, protease inhibitor, peptidase, chitinase, and lipases as well as the low molecular weight secondary compounds ellagic acid and quercetin rhamnoside. SEX inhibited H. contortus larval development (LDA) (IC₅₀ = 0.29 mg mL^-1), but did not affect larval exsheathment (LEIA). On the other hand, although SEXF1 and SEXF2 inhibited H. contortus LEIA (IC₅₀ = 1.04 and 0.93 mg mL^-1, respectively), they showed even greater inhibition efficiency of H. contortus larval development (IC₅₀ = 0.29 and 0.42 mg mL^-1, respectively). To the best of our knowledge, this study is the first to show the anthelmintic activity of plant exudates against a gastrointestinal nematode. Moreover, it suggests the potential of exuded proteins as candidates to negatively interfere with H. contortus life cycle.

Potassium, not lepidimoide, is the principal 'allelochemical' of cress-seed exudate that promotes amaranth hypocotyl elongation

BACKGROUND AND AIMS

Imbibed cress ( Lepidium sativum L.) seeds exude 'allelochemicals' that promote excessive hypocotyl elongation and inhibit root growth in neighbouring competitors, e.g. amaranth ( Amaranthus caudatus L.) seedlings. The major hypocotyl promoter has recently been shown not to be the previously suggested acidic disaccharide, lepidimoic acid (LMA), a fragment of the pectic polysaccharide domain rhamnogalacturonan-I. The nature of the hypocotyl promoter has now been re-assessed.

METHODS

Low-molecular weight cress-seed exudate (LCSE) was fractionated by high-voltage electrophoresis, and components with different charge:mass ratios were tested for effects on dark-grown amaranth seedlings. Further samples of LCSE were size-fractionated by gel permeation chromatography, and active fractions were analysed electrophoretically.

KEY RESULTS

The LCSE strongly promoted amaranth hypocotyl elongation. The active principle was hydrophilic and, unlike LMA, stable to hot acid. After electrophoresis at pH 6·5, the only fractions that strongly promoted hypocotyl elongation were those with a very high positive charge:mass ratio, migrating towards the cathode 3-4 times faster than glucosamine. Among numerous naturally occurring cations tested, the only one with such a high mobility was potassium. K + was present in LCSE at approx. 4 m m , and pure KCl (1-10 m m ) strongly promoted amaranth hypocotyl elongation. No other cation tested (including Na + , spermidine and putrescine) had this effect. The peak of bioactivity from a gel permeation chromatography column exactly coincided with the peak of K + .

CONCLUSIONS

The major 'allelopathic' substance present in cress-seed exudate that stimulates hypocotyl elongation in neighbouring seedlings is the inorganic cation, K + , not the oligosaccharin LMA.

Comprehensive analysis of response and tolerant mechanisms in early-stage soybean at initial-flooding stress

Soybean is one of the most cultivated crops in the world; however, it is very sensitive to flooding stress, which markedly reduces its growth and yield. Morphological and biochemical changes such as an increase of fresh weight and a decrease of ATP content happen in early-stage soybean at initial-flooding stress, indicating that soybean responses to flooding stress are keys for its survival and seedling growth. Phosphoproteomics and nuclear proteomics are useful tools to detect protein-phosphorylation status and to identify transcriptional factors. In the review, the effect of flooding on soybean response to initial flooding stress is discussed based on recent results of proteomic, phosphoproteomic, nuclear proteomic, and nuclear phosphoproteomic studies. In addition, soybean survival under flooding stress, which is defined as tolerance mechanism, is discussed with the results of comprehensive analysis in flooding-tolerant mutant line and abscisic acid-treated soybean.

BIOLOGICAL SIGNIFICANCE

Soybean is one of the most cultivated crops in the world; however, it is very sensitive to flooding stress, especially soybean responses to initial flooding stress is key for its survival and seedling growth. Recently, proteomic techniques are applied to investigate the response and tolerant mechanisms of soybean at initial flooding condition. In this review, the progress in proteomic, phosphoproteomic, nuclear proteomic, and nuclear phosphoproteomic studies about the initial-flooding response mechanism in early-stage soybean is presented. In addition, the tolerant mechanism in soybean is discussed with the results of comprehensive analysis in flooding-tolerant mutant line and abscisic acid-treated soybean. Through this review, the key proteins and genes involved in initial flooding response and tolerance at early stage soybean are summarized and they contribute greatly to uncover response and tolerance mechanism at early stage under stressful environmental conditions in soybean.

Proteins in Relation to Vigor and Viability of White Lupin (Lupinus albus L.) Seed Stored for 26 Years

The aim of the study was to evaluate the vigor and viability as well as to determine and compare the contents of selected protein fractions of white lupin (Lupinus albus L.) seeds stored for 26 years at temperatures of -14°C and +20°C. The seeds stored at -14°C germinated in 86.3%, while the seeds stored at +20°C did not germinate at all. The viability evaluation was confirmed by the measuring electroconductivity of seed exudates. In seeds stored at -14°C the contents of γ, δ, and β conglutin were 14, 4 and 69 mg g^-1 fresh mass, respectively, while in seed stored at +20°C they were 15.5, 3, 65 mg g^-1 fresh mass, respectively. One-dimensional electrophoresis of γ and δ conglutin fractions indicated the presence of several intense polypeptide bands with molecular weights from 23.0 to 10.3 kDa. Polypeptide bands with a molecular weight of 22.4 and 19.8 kDa exhibited almost two times higher expression in the seeds stored at -14°C compared to the seeds stored at +20°C. Electrophoresis revealed 310 protein spots on the maps generated for seeds stored at -14°C, and 228 spots for seeds stored at +20°C. In seeds stored at +20°C most polypeptide subunits had a pI ranging from 4.5 to 7 and a molecular weight of 10-97 kDa. The greatest differences in the contents of polypeptides between the analyzed variants was observed within the range of 20-45 kDa (-14°C: 175, +20°C: 115 protein spots) and within the range of 65-97 kDa (-14°C: 103, +20°C: 75 protein spots). In seeds stored at +20°C, a clear decline in basic (8-10 pI) polypeptides was observed. The study demonstrated that the polypeptides identified as γ and δ conglutins are probably closely related to vigor and viability of seeds.

Narrow-Leafed Lupin (Lupinus angustifolius) β1- and β6-Conglutin Proteins Exhibit Antifungal Activity, Protecting Plants against Necrotrophic Pathogen Induced Damage from Sclerotinia sclerotiorum and Phytophthora nicotianae

Vicilins (7S globulins) are seed storage proteins and constitute the main protein family in legume seeds, particularly in narrow-leafed lupin (Lupinus angustifolius L.; NLL), where seven vicilin genes, called β1- to β7-conglutin have been identified. Vicilins are involved in germination processes supplying amino acids for seedling growth and plant development, as well as in some cases roles in plant defense and protection against pathogens. The roles of NLL β-conglutins in plant defense are unknown. Here the potential role of five NLL β-conglutin family members in protection against necrotrophic fungal pathogens was investigated and it was demonstrated that recombinant purified 6xHis-tagged β1- and β6-conglutin proteins exhibited the strongest in vitro growth inhibitory activity against a range of necrotrophic fungal pathogens compared to β2, β3, and β4 conglutins. To examine activity in vivo, two representative necrotrophic pathogens, the fungus Sclerotinia sclerotiorum and oomycete Phytophthora nicotianae were used. Transient expression of β1- and β6-conglutin proteins in Nicotiana benthamiana leaves demonstrated in vivo growth suppression of both of these pathogens, resulting in low percentages of hyphal growth and elongation in comparison to control treated leaves. Cellular studies using β1- and β6-GFP fusion proteins showed these conglutins localized to the cell surface including plasmodesmata. Analysis of cellular death following S. sclerotiorum or P. nicotianae revealed both β1- and β6-conglutins suppressed pathogen induced cell death in planta and prevented pathogen induced suppression of the plant oxidative burst as determined by protein oxidation in infected compared to mock-inoculated leaves.

Structural basis of the lack of endo-glucanase inhibitory activity of Lupinus albus γ-conglutin

Lupin γ-conglutin and soybean BG7S are two legume seed proteins strongly similar to plant endo-β-glucanases inhibitors acting against fungal GH11 and GH12 glycoside hydrolase. However these proteins lack inhibitory activity. Here we describe the conversion of lupin γ-conglutin to an active inhibitor of endo-β-glucanases belonging to GH11 family. A set of γ-conglutin mutants was designed and expressed in Pichia pastoris, along with the wild-type protein. Unexpectedly, this latter was able to inhibit a GH11 enzyme, but not GH12, whereas the mutants were able to modulate the inhibition capacity. In lupin, γ-conglutin is naturally cleaved in two subunits, whereas in P. pastoris it is not. The lack of proteolytic cleavage is one of the reasons at the basis of the inhibitory activity of recombinant γ-conglutin. The results provide new insights about structural features at the basis of the lack of inhibitory activity of wild-type γ-conglutin and its legume homologues.

A review: what is the spermosphere and how can it be studied?

The spermosphere is the zone surrounding seeds where interactions between the soil, microbial communities and germinating seeds take place. The concept of the spermosphere is usually only applied during germination sensu stricto. Despite the transient nature of this very small zone of soil around the germinating seed, the microbial activities which occur there may have long-lasting impacts on plants. The spermosphere is indirectly characterized by either (i) seed exudates, which could be inhibitors or stimulators of micro-organism growth or (ii) the composition of the microbiome on and around the germinating seeds. The microbial communities present in the spermosphere directly reflect that of the germination medium or are host-dependent and influenced quantitatively and qualitatively by host exudates. Despite its strong impact on the future development of plants, the spermosphere remains little studied. This can be explained by the technical difficulties related to characterizing this concept due to its short duration, small size and biomass, and the number and complexity of the interactions that take place. However, recent technical methods, such as metabolite profiling, combining phenotypic methods with DNA- and RNA-based methods, could be used to investigate seed exudates, microbial communities and their interactions with the soil environment.

Understanding pea resistance mechanisms in response to Fusarium oxysporum through proteomic analysis

Fusarium oxysporum f. sp. pisi (Fop) is an important and destructive pathogen affecting pea crop (Pisum sativum) throughout the world. Control of this disease is achieved mainly by integration of different disease management procedures. However, the constant evolution of the pathogen drives the necessity to broaden the molecular basis of resistance to Fop. Our proteomic study was performed on pea with the aim of identifying proteins involved in different resistance mechanisms operating during F. oxysporum infection. For such purpose, we used a two-dimensional electrophoresis (2-DE) coupled to mass spectrometry (MALDI-TOF/TOF) analysis to study the root proteome of three pea genotypes showing different resistance response to Fop race 2. Multivariate statistical analysis identified 132 differential protein spots under the experimental conditions (genotypes/treatments). All of these protein spots were subjected to mass spectrometry analysis to deduce their possible functions. A total of 53 proteins were identified using a combination of peptide mass fingerprinting (PMF) and MSMS fragmentation. The following main functional categories were assigned to the identified proteins: carbohydrate and energy metabolism, nucleotides and aminoacid metabolism, signal transduction and cellular process, folding and degradation, redox and homeostasis, defense, biosynthetic process and transcription/translation. Results obtained in this work suggest that the most susceptible genotypes have increased levels of enzymes involved in the production of reducing power which could then be used as cofactor for enzymes of the redox reactions. This is in concordance with the fact that a ROS burst occurred in the same genotypes, as well as an increase of PR proteins. Conversely, in the resistant genotype proteins responsible to induce changes in the membrane and cell wall composition related to reinforcement were identified. Results are discussed in terms of the differential response to Fop.

Proteome of Soybean Seed Exudates Contains Plant Defense-Related Proteins Active against the Root-Knot Nematode Meloidogyne incognita

Several studies have described the effects of seed exudates against microorganisms, but only few of them have investigated the proteins that have defensive activity particularly against nematode parasites. This study focused on the proteins released in the exudates of soybean seeds and evaluated their nematicidal properties against Meloidogyne incognita. A proteomic approach indicated the existence of 63 exuded proteins, including β-1,3-glucanase, chitinase, lectin, trypsin inhibitor, and lipoxygenase, all of which are related to plant defense. The presence of some of these proteins was confirmed by their in vitro activity. The soybean exudates were able to reduce the hatching of nematode eggs and to cause 100% mortality of second-stage juveniles (J2). The pretreatment of J2 with these exudates resulted in a 90% reduction of the gall number in tobacco plants. These findings suggest that the exuded proteins are directly involved in plant defense against soil pathogens, including nematodes, during seed germination.

Analysis of initial changes in the proteins of soybean root tip under flooding stress using gel-free and gel-based proteomic techniques

Flooding has a severe negative effect on soybean cultivation in the early stages of growth. To obtain a better understanding of the response mechanisms of soybean to flooding stress, initial changes in root tip proteins under flooding were analyzed using two proteomic techniques. Two-day-old soybeans were treated with flooding for 3, 6, 12, and 24h. The weight of soybeans increased during the first 3h of flooding, but root elongation was not observed. Using gel-based and gel-free proteomic techniques, 115 proteins were identified in root tips, of which 9 proteins were commonly detected by both methods. The 71 proteins identified by the gel-free proteomics were analyzed by a hierarchical clustering method based on induction levels during the flooding, and the proteins were divided into 5 clusters. Additional interaction analysis of the proteins revealed that ten proteins belonging to cluster I formed the center of a protein interaction network. mRNA expression analysis of these ten proteins showed that citrate lyase and heat shock protein 70 were down-regulated, whereas calreticulin was up-regulated in initial phase of flooding. These results suggest that flooding stress to soybean induces calcium-related signal transduction, which might play important roles in the early responses to flooding.

BIOLOGICAL SIGNIFICANCE

Flooding has a severe negative effect on soybean cultivation, particularly in the early stages of growth. To better understand the response mechanisms of soybean to the early stages of flooding stress, two proteomic techniques were used. Two-day-old soybeans were treated without or with flooding for 3, 6, 12, and 24h. The fresh weight of soybeans increased during the first 3h of flooding stress, but the growth then slowed and no root elongation was observed. Using gel-based and gel-free proteomic techniques, 115 proteins were identified in root tips, of which 9 proteins were commonly detected by both methods. The 71 proteins identified by the gel-free proteomics were analyzed by a hierarchical clustering method based on induction levels during the flooding stress, and 5 protein clusters were recognized. Protein interaction analysis revealed that ten proteins belonging to cluster I formed the center of a protein interaction network. mRNA expression analysis of these ten proteins showed that citrate lyase and heat shock protein 70 were down-regulated in response to flooding stress, whereas calreticulin was up-regulated. These results suggest that flooding stress to soybean induces calcium-related signal transduction, which might play important roles in the early responses to flooding.