Plant defensins: defense, development and application

Antimicrobial Peptides - Small but Mighty Weapons for Plants to Fight Phytopathogens

Antimicrobial Peptides (AMPs) have diverse structures, varied modes of actions, and can inhibit the growth of a wide range of pathogens at low concentrations. Plants are constantly under attack by a wide range of phytopathogens causing massive yield losses worldwide. To combat these pathogens, nature has armed plants with a battery of defense responses including Antimicrobial Peptides (AMPs). These peptides form a vital component of the two-tier plant defense system. They are constitutively expressed as part of the pre-existing first line of defense against pathogen entry. When a pathogen overcomes this barrier, it faces the inducible defense system, which responds to specific molecular or effector patterns by launching an arsenal of defense responses including the production of AMPs. This review emphasizes the structural and functional aspects of different plant-derived AMPs, their homology with AMPs from other organisms, and how their biotechnological potential could generate durable resistance in a wide range of crops against different classes of phytopathogens in an environmentally friendly way without phenotypic cost.

Antimicrobial peptides: new hope in the war against multidrug resistance

The discovery of antibiotics marked a golden age in the revolution of human medicine. However, decades later, bacterial infections remain a global healthcare threat, and a return to the pre-antibiotic era seems inevitable if stringent measures are not adopted to curb the rapid emergence and spread of multidrug resistance and the indiscriminate use of antibiotics. In hospital settings, multidrug resistant (MDR) pathogens, including carbapenem-resistant Pseudomonas aeruginosa, vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA), and extended-spectrum β-lactamases (ESBL) bearing Acinetobacter baumannii, Escherichia coli, and Klebsiella pneumoniae are amongst the most problematic due to the paucity of treatment options, increased hospital stay, and exorbitant medical costs. Antimicrobial peptides (AMPs) provide an excellent potential strategy for combating these threats. Compared to empirical antibiotics, they show low tendency to select for resistance, rapid killing action, broad-spectrum activity, and extraordinary clinical efficacy against several MDR strains. Therefore, this review highlights multidrug resistance among nosocomial bacterial pathogens and its implications and reiterates the importance of AMPs as next-generation antibiotics for combating MDR superbugs.

Molecular and genetic analysis of defensive responses of Brassica juncea - B. fruticulosa introgression lines to Sclerotinia infection

Sclerotinia stem rot caused by Sclerotinia sclerotiorum is a major disease of crop brassicas, with inadequate variation for resistance in primary gene pools. We utilized a wild Brassicaceae species with excellent resistance against stem rot to develop a set of B. juncea - B. fruticulosa introgression lines (ILs). These were assessed for resistance using a highly reproducible stem inoculation technique against a virulent pathogen isolate. Over 40% of ILs showed higher levels of resistance. IL-43, IL-175, IL-215, IL-223 and IL-277 were most resistant ILs over three crop seasons. Sequence reads (21x) from the three most diverse ILs were then used to create B. juncea pseudomolecules, by replacing SNPs of reference B. juncea with those of re-sequenced ILs. Genotyping by sequencing (GBS) was also carried out for 88 ILs. Resultant sequence tags were then mapped on to the B. juncea pseudomolecules, and SNP genotypes prepared for each IL. Genome wide association studies helped to map resistance responses to stem rot. A total of 13 significant loci were identified on seven B. juncea chromosomes (A01, A03, A04, A05, A08, A09 and B05). Annotation of the genomic region around identified SNPs allowed identification of 20 candidate genes belonging to major disease resistance protein families, including TIR-NBS-LRR class, Chitinase, Malectin/receptor-like protein kinase, defensin-like (DEFL), desulfoglucosinolate sulfotransferase protein and lipoxygenase. A majority of the significant SNPs could be validated using whole genome sequences (21x) from five advanced generation lines being bred for Sclerotinia resistance as compared to three susceptible B. juncea germplasm lines. Our findings not only provide critical new understanding of the defensive pathway of B. fruticulosa resistance, but will also enable development of marker candidates for assisted transfer of introgressed resistant loci in to agronomically superior cultivars of crop Brassica.

A Role for Zinc in Plant Defense Against Pathogens and Herbivores

Pests and diseases pose a threat to food security, which is nowadays aggravated by climate change and globalization. In this context, agricultural policies demand innovative approaches to more effectively manage resources and overcome the ecological issues raised by intensive farming. Optimization of plant mineral nutrition is a sustainable approach to ameliorate crop health and yield. Zinc is a micronutrient essential for all living organisms with a key role in growth, development, and defense. Competition for Zn affects the outcome of the host-attacker interaction in both plant and animal systems. In this review, we provide a clear framework of the different strategies involving low and high Zn concentrations launched by plants to fight their enemies. After briefly introducing the most relevant macro- and micronutrients for plant defense, the functions of Zn in plant protection are summarized with special emphasis on superoxide dismutases (SODs) and zinc finger proteins. Following, we cover recent meaningful studies identifying Zn-related passive and active mechanisms for plant protection. Finally, Zn-based strategies evolved by pathogens and pests to counteract plant defenses are discussed.

Wheat wounding-responsive HD-Zip IV transcription factor GL7 is predominantly expressed in grain and activates genes encoding defensins

Several classes of transcription factors are involved in the activation of defensins. A new type of the transcription factor responsible for the regulation of wheat grain specific defensins was characterised in this work. HD-Zip class IV transcription factors constitute a family of multidomain proteins. A full-length cDNA of HD-Zip IV, designated TaGL7 was isolated from the developing grain of bread wheat, using a specific DNA sequence as bait in the Y1H screen. 3D models of TaGL7 HD complexed with DNA cis-elements rationalised differences that underlined accommodations of binding and non-binding DNA, while the START-like domain model predicted binding of lipidic molecules inside a concave hydrophobic cavity. The 3'-untranslated region of TaGL7 was used as a probe to isolate the genomic clone of TdGL7 from a BAC library prepared from durum wheat. The spatial and temporal activity of the TdGL7 promoter was tested in transgenic wheat, barley and rice. TdGL7 was expressed mostly in ovary at fertilisation and its promoter was active in a liquid endosperm during cellularisation and later in the endosperm transfer cells, aleurone, and starchy endosperm. The pattern of TdGL7 expression resembled that of genes that encode grain-specific lipid transfer proteins, particularly defensins. In addition, GL7 expression was upregulated by mechanical wounding, similarly to defensin genes. Co-bombardment of cultured wheat cells with TdGL7 driven by constitutive promoter and seven grain or root specific defensin promoters fused to GUS gene, revealed activation of four promoters. The data confirmed the previously proposed role of HD-Zip IV transcription factors in the regulation of genes that encode lipid transfer proteins involved in lipid transport and defence. The TdGL7 promoter could be used to engineer cereal grains with enhanced resistance to insects and fungal infections.

Antimicrobial peptide ROAD-1 triggers phase change in local membrane environment to execute its activity

Emergence of antibiotic-resistant pathogens has paved way for development of newer class of drugs that would not be susceptible to resistance. Antimicrobial peptides such as defensins that target the microbial membrane are promising candidates. ROAD-1 is an alpha-defensin present in the oral cavity of rhesus macaque and shares very high sequence similarity to human enteric defensin 5. In this study we have performed microsecond long all atom molecular dynamic simulations to understand the mechanism of action of ROAD-1. We find that ROAD-1 is able to adopt an energetically stable conformation predominantly stabilized by electrostatic interactions only in presence of bacterial membranes. In mammalian membrane even though it gets absorbed onto the bilayer, it is unable to adopt an equilibrium conformation. Binding of ROAD-1 to bilayer induces clustering of POPG molecules up to 15 Å around the peptide. POPG molecules show higher order parameters than the neighboring POPE implying coexistence of different phases. Analysis of binding free energy of ROAD-1-membrane complex indicates Arg1, Arg2, Arg7, and Arg25 to play key role in its antimicrobial activity. Unlike its homolog HD5, ROAD-1 is not observed to form a dimer. Our study gives insight into the membrane-bound conformation of ROAD-1 and its mechanism of action that can aid in designing defensin-based therapeutics. Graphical abstract Antimicrobial peptide ROAD-1 adopts a different membrane-bound conformation as compared with HD5 even though they belong to the same family implying a different mechanism of action.

The mitochondrial oxidation resistance protein AtOXR2 increases plant biomass and tolerance to oxidative stress

This study demonstrates the existence of the oxidation resistance (OXR) protein family in plants. There are six OXR members in Arabidopsis that contain the highly conserved TLDc domain that is characteristic of this eukaryotic protein family. AtOXR2 is a mitochondrial protein able to alleviate the stress sensitivity of a yeast oxr1 mutant. It was induced by oxidative stress and its overexpression in Arabidopsis (oeOXR2) increased leaf ascorbate, photosynthesis, biomass, and seed production, as well as conferring tolerance to methyl viologen, antimycin A, and high light intensities. The oeOXR2 plants also showed higher ABA content, changes in ABA sensitivity, and modified expression of ABA- and stress-regulated genes. While the oxr2 mutants had a similar shoot phenotype to the wild-type, they exhibited increased sensitivity to stress. We propose that by influencing the levels of reactive oxygen species (ROS), AtOXR2 improves the efficiency of photosynthesis and elicits basal tolerance to environmental challenges that increase oxidative stress, allowing improved plant growth and biomass production.

Root extracellular traps versus neutrophil extracellular traps in host defence, a case of functional convergence?

The root cap releases cells that produce massive amounts of mucilage containing polysaccharides, proteoglycans, extracellular DNA (exDNA) and a variety of antimicrobial compounds. The released cells - known as border cells or border-like cells - and mucilage secretions form networks that are defined as root extracellular traps (RETs). RETs are important players in root immunity. In animals, phagocytes are some of the most abundant white blood cells in circulation and are very important for immunity. These cells combat pathogens through multiple defence mechanisms, including the release of exDNA-containing extracellular traps (ETs). Traps of neutrophil origin are abbreviated herein as NETs. Similar to phagocytes, plant root cap-originating cells actively contribute to frontline defence against pathogens. RETs and NETs are thus components of the plant and animal immune systems, respectively, that exhibit similar compositional and functional properties. Herein, we describe and discuss the formation, molecular composition and functional similarities of these similar but different extracellular traps.

Lignin biosynthesis as a key mechanism to repress Polystigma amygdalinum, the causal agent of the red leaf blotch disease in almond

The red leaf blotch (RLB) of almond, caused by the fungus Polystigma amygdalinum, is considered as one of the most important leaf diseases of this fruit tree. Differential cultivar susceptibility to the RLB has been described based on field observations, while its molecular and biochemical bases remain unknown to date. We aimed to explore the plant defence mechanisms related to the cultivar susceptibility by identifying some relevant physical and chemical strategies for the pathogen control. Thus, we studied the regulation of seven defence-related genes as well as the lignin deposition in two almond cultivars with highly differential response to RLB: the highly tolerant 'Mardía' and the susceptible 'Tarraco' cultivars. 'Mardía' displayed an up-regulation of the CAD and DFN1 genes at early stages of RLB symptom expression, with further lignin deposition in the fungal-colonized area that was visualized by microscopy. Thus, 'Mardía' uses both physical and chemical responses to effectively repress the pathogen. In contrast, 'Tarraco' triggered the up-regulation of HQT and LDOX genes, related to chlorogenic acid and anthocyanin biosynthesis pathways, respectively, while lignin deposition was not clearly noticed. This strategy recorded in 'Tarraco' at later stages of RLB symptoms failed to control the fungal infection and colonization. Our results suggested a major role of the phenylpropanoids pathway in the defence response against RLB, by showing that an early production of lignin might be a major mechanism to control the spread of P. amygdalinum within the host leaf tissues.

Plant defensins: types, mechanism of action and prospects of genetic engineering for enhanced disease resistance in plants

Natural antimicrobial peptides have been shown as one of the important tools to combat certain pathogens and play important role as a part of innate immune system in plants and, also adaptive immunity in animals. Defensin is one of the antimicrobial peptides with a diverse nature of mechanism against different pathogens like viruses, bacteria and fungi. They have a broad function in humans, vertebrates, invertebrates, insects, and plants. Plant defensins primarily interact with membrane lipids for their biological activity. Several antimicrobial peptides (AMPs) have been overexpressed in plants for enhanced disease protection. The plants defensin peptides have been efficiently employed as an effective strategy for control of diseases in plants. They can be successfully integrated in plants genome along with some other peptide genes in order to produce transgenic crops for enhanced disease resistance. This review summarizes plant defensins, their expression in plants and enhanced disease resistance potential against phytopathogens.

Ribosomal Peptides and Small Proteins on the Rise

Genetically encoded and ribosomally synthesised peptides and small proteins act as important regulators in fundamental cellular processes, including gene expression, development, signalling and metabolism. Moreover, they also play a crucial role in eukaryotic and prokaryotic defence against microorganisms. Extremely diverse in size and structure, they are often subject to extensive post-translational modification. Recent technological advances are now allowing the analysis of the whole cellular transcriptome and proteome, revealing the presence of hundreds of long-overlooked alternative and short open reading frames (short ORFs, or sORFs) in mRNA and supposedly noncoding RNAs. However, in many instances the biological roles of their translational products remain to be elucidated. Here we provide an overview on the intriguing structural and functional diversity of ribosomally synthesised peptides and newly discovered peptides and small proteins.

A structural perspective of plant antimicrobial peptides

Among the numerous strategies plants have developed to fend off enemy attack, antimicrobial peptides (AMPs) stand out as one of the most prominent defensive barriers that grant direct and durable resistance against a wide range of pests and pathogens. These small proteins are characterized by a compact structure and an overall positive charge. AMPs have an ancient origin and widespread occurrence in the plant kingdom but show an unusually high degree of variation in their amino acid sequences. Interestingly, there is a strikingly conserved topology among the plant AMP families, suggesting that the defensive properties of these peptides are not determined by their primary sequences but rather by their tridimensional structure. To explore and expand this idea, we here discuss the role of AMPs for plant defense from a structural perspective. We show how specific structural properties, such as length, charge, hydrophobicity, polar angle and conformation, are essential for plant AMPs to act as a chemical shield that hinders enemy attack. Knowledge on the topology of these peptides is facilitating the isolation, classification and even structural redesign of AMPs, thus allowing scientists to develop new peptides with multiple agronomical and pharmacological potential.

Sensitisation to outdoor and indoor fungi in atopic dermatitis patients and the relation to the occurrence of food allergy to peanuts and walnuts

The aim of this study is the evaluation of the relation between the sensitisation to outdoor and indoor fungi and allergy to peanuts and walnuts in atopic dermatitis patients aged 14 years and older. The complete dermatological and allergological examinations were performed in all included patients; the occurrence of food allergy to peanuts and walnuts was recorded (specific IgE, skin prick test, history of allergic reaction) and the sensitisation to mixture of outdoor fungi and indoor fungi was also examined (skin prick test, specific IgE). The statistical evaluation of the relation between the sensitisation to outdoor and indoor fungi and the occurrence of food allergy to peanuts and walnuts was performed; 329 patients were included in the study, 110 men and 219 women, the average age 26.8 years. The sensitisation to outdoor fungi was recorded in 91 patients (28%), the sensitisation to indoor fungi was recorded in 61 patients (18.5%), the occurrence of food allergy to peanuts was confirmed in 90 (27%) patients and to walnuts in 121 (36.7%) patients. We confirmed, that patients suffering from sensitisation to outdoor fungi suffer significantly more from food allergy to peanuts and walnuts. The significant relation between the sensitisation to indoor fungi and food allergy to peanuts and walnuts was not confirmed.

Membrane Active Peptides and Their Biophysical Characterization

In the last 20 years, an increasing number of studies have been reported on membrane active peptides. These peptides exert their biological activity by interacting with the cell membrane, either to disrupt it and lead to cell lysis or to translocate through it to deliver cargos into the cell and reach their target. Membrane active peptides are attractive alternatives to currently used pharmaceuticals and the number of antimicrobial peptides (AMPs) and peptides designed for drug and gene delivery in the drug pipeline is increasing. Here, we focus on two most prominent classes of membrane active peptides; AMPs and cell-penetrating peptides (CPPs). Antimicrobial peptides are a group of membrane active peptides that disrupt the membrane integrity or inhibit the cellular functions of bacteria, virus, and fungi. Cell penetrating peptides are another group of membrane active peptides that mainly function as cargo-carriers even though they may also show antimicrobial activity. Biophysical techniques shed light on peptide–membrane interactions at higher resolution due to the advances in optics, image processing, and computational resources. Structural investigation of membrane active peptides in the presence of the membrane provides important clues on the effect of the membrane environment on peptide conformations. Live imaging techniques allow examination of peptide action at a single cell or single molecule level. In addition to these experimental biophysical techniques, molecular dynamics simulations provide clues on the peptide–lipid interactions and dynamics of the cell entry process at atomic detail. In this review, we summarize the recent advances in experimental and computational investigation of membrane active peptides with particular emphasis on two amphipathic membrane active peptides, the AMP melittin and the CPP pVEC.

Disease Resistance Mechanisms in Plants

Plants have developed a complex defense system against diverse pests and pathogens. Once pathogens overcome mechanical barriers to infection, plant receptors initiate signaling pathways driving the expression of defense response genes. Plant immune systems rely on their ability to recognize enemy molecules, carry out signal transduction, and respond defensively through pathways involving many genes and their products. Pathogens actively attempt to evade and interfere with response pathways, selecting for a decentralized, multicomponent immune system. Recent advances in molecular techniques have greatly expanded our understanding of plant immunity, largely driven by potential application to agricultural systems. Here, we review the major plant immune system components, state of the art knowledge, and future direction of research on plant⁻pathogen interactions. In our review, we will discuss how the decentralization of plant immune systems have provided both increased evolutionary opportunity for pathogen resistance, as well as additional mechanisms for pathogen inhibition of such defense responses. We conclude that the rapid advances in bioinformatics and molecular biology are driving an explosion of information that will advance agricultural production and illustrate how complex molecular interactions evolve.

Classes, Databases, and Prediction Methods of Pharmaceutically and Commercially Important Cystine-Stabilized Peptides

Cystine-stabilized peptides represent a large family of peptides characterized by high structural stability and bactericidal, fungicidal, or insecticidal properties. Found throughout a wide range of taxa, this broad and functionally important family can be subclassified into distinct groups dependent upon their number and type of cystine bonding patters, tertiary structures, and/or their species of origin. Furthermore, the annotation of proteins related to the cystine-stabilized family are under-represented in the literature due to their difficulty of isolation and identification. As a result, there are several recent attempts to collate them into data resources and build analytic tools for their dynamic prediction. Ultimately, the identification and delivery of new members of this family will lead to their growing inclusion into the repertoire of commercial viable alternatives to antibiotics and environmentally safe insecticides. This review of the literature and current state of cystine-stabilized peptide biology is aimed to better describe peptide subfamilies, identify databases and analytics resources associated with specific cystine-stabilized peptides, and highlight their current commercial success.

Host defense peptides: An insight into the antimicrobial world

A serious challenge to antimicrobial therapies has emerged due to rapid increase in drug-resistant infections creating an urge for the development of alternative therapeutics. Antimicrobial peptides (AMPs) have gained importance because of their broad-spectrum antimicrobial activities and mediator-like functions linking innate and adaptive immune responses. The multidimensional properties of these peptides hold promising potentials as prophylactic and antimicrobial agents. This review discusses various AMPs and their role in combating microorganisms and infections along with its clinical implication.

The potential of component-resolved diagnosis in laboratory diagnostics of allergy

The initial laboratory approach in the diagnosis of allergies is to detect the type of allergic reaction, i.e. whether the patient’s allergy is mediated by immunoglobulin E (IgE) or not. For this purpose, the concentration of total serum IgE (tIgE) and specific IgE (sIgE) are determined. Progress in laboratory diagnostics is the use of component-resolved diagnosis (CRD) which implies determination of sIgE against purified native and recombinant allergenic molecules. Component-resolved diagnosis is used in laboratory practice as singleplex and multiplex assays. The choice of allergen for singleplex assay is based on anamnesis, clinical findings of a patient and on skin prick test results. Multiplex-microarray assays simultaneously determine multiple sIgE’s against numerous allergens. The goal of CRD is to distinguish the true allergens from the cross-reactive allergen molecules. Component-resolved diagnosis allows predicting the risk of severe symptoms, as well as anticipating the development of allergies. Thus, determination of sIgE against allergenic components may significantly improve current diagnostics of allergy. Since this method is applied in laboratory practice just a few years, it is necessary to acquire new knowledge and experience, to establish good co-operation between specialist in medical biochemistry and laboratory medicine and the specialist allergologist, so that the method can be applied in a rational manner. Component-resolved diagnosis will significantly improve the diagnostics of IgE-mediated allergy in the future. The aim of this article is to present potentials of CRD in the laboratory diagnostics of allergy mediated by IgE.

Antimicrobial Peptides: Diversity, Mechanism of Action and Strategies to Improve the Activity and Biocompatibility In Vivo

Antibiotic resistance is projected as one of the greatest threats to human health in the future and hence alternatives are being explored to combat resistance. Antimicrobial peptides (AMPs) have shown great promise, because use of AMPs leads bacteria to develop no or low resistance. In this review, we discuss the diversity, history and the various mechanisms of action of AMPs. Although many AMPs have reached clinical trials, to date not many have been approved by the US Food and Drug Administration (FDA) due to issues with toxicity, protease cleavage and short half-life. Some of the recent strategies developed to improve the activity and biocompatibility of AMPs, such as chemical modifications and the use of delivery systems, are also reviewed in this article.

Transcriptome analysis of response to Plasmodiophora brassicae infection in the Arabidopsis shoot and root

BACKGROUND

Clubroot is an important disease caused by the obligate parasite Plasmodiophora brassicae that infects the Brassicaceae. As a soil-borne pathogen, P. brassicae induces the generation of abnormal tissue in the root, resulting in the formation of galls. Root infection negatively affects the uptake of water and nutrients in host plants, severely reducing their growth and productivity. Many studies have emphasized the molecular and physiological effects of the clubroot disease on root tissues. The aim of the present study is to better understand the effect of P. brassicae on the transcriptome of both shoot and root tissues of Arabidopsis thaliana.

RESULTS

Transcriptome profiling using RNA-seq was performed on both shoot and root tissues at 17, 20 and 24 days post inoculation (dpi) of A. thaliana, a model plant host for P. brassicae. The number of differentially expressed genes (DEGs) between infected and uninfected samples was larger in shoot than in root. In both shoot and root, more genes were differentially regulated at 24 dpi than the two earlier time points. Genes that were highly regulated in response to infection in both shoot and root primarily were involved in the metabolism of cell wall compounds, lipids, and shikimate pathway metabolites. Among hormone-related pathways, several jasmonic acid biosynthesis genes were upregulated in both shoot and root tissue. Genes encoding enzymes involved in cell wall modification, biosynthesis of sucrose and starch, and several classes of transcription factors were generally differently regulated in shoot and root.

CONCLUSIONS

These results highlight the similarities and differences in the transcriptomic response of above- and below-ground tissues of the model host Arabidopsis following P. brassicae infection. The main transcriptomic changes in root metabolism during clubroot disease progression were identified. An overview of DEGs in the shoot underlined the physiological changes in above-ground tissues following pathogen establishment and disease progression. This study provides insights into host tissue-specific molecular responses to clubroot development and may have applications in the development of clubroot markers for more effective breeding strategies.

Comparative transcriptome and metabolome analysis suggests bottlenecks that limit seed and oil yields in transgenic Camelina sativa expressing diacylglycerol acyltransferase 1 and glycerol-3-phosphate dehydrogenase

BACKGROUND

Camelina sativa has attracted much interest as alternative renewable resources for biodiesel, other oil-based industrial products and a source for edible oils. Its unique oil attributes attract research to engineering new varieties of improved oil quantity and quality. The overexpression of enzymes catalyzing the synthesis of the glycerol backbone and the sequential conjugation of fatty acids into this backbone is a promising approach for increasing the levels of triacylglycerol (TAG). In a previous study, we co-expressed the diacylglycerol acyltransferase (DGAT1) and glycerol-3-phosphate dehydrogenase (GPD1), involved in TAG metabolism, in Camelina seeds. Transgenic plants exhibited a higher-percentage seed oil content, a greater seed mass, and overall improved seed and oil yields relative to wild-type plants. To further increase seed oil content in Camelina, we utilized metabolite profiling, in conjunction with transcriptome profiling during seed development to examine potential rate-limiting step(s) in the production of building blocks for TAG biosynthesis.

RESULTS

Transcriptomic analysis revealed approximately 2518 and 3136 transcripts differentially regulated at significant levels in DGAT1 and GPD1 transgenics, respectively. These transcripts were found to be involved in various functional categories, including alternative metabolic routes in fatty acid synthesis, TAG assembly, and TAG degradation. We quantified the relative contents of over 240 metabolites. Our results indicate major metabolic switches in transgenic seeds associated with significant changes in the levels of glycerolipids, amino acids, sugars, and organic acids, especially the TCA cycle and glycolysis intermediates.

CONCLUSIONS

From the transcriptomic and metabolomic analysis of DGAT1, GPD1 and DGAT1 + GPD1 expressing lines of C. sativa, we conclude that TAG production is limited by (1) utilization of fixed carbon from the source tissues supported by the increase in glycolysis pathway metabolites and decreased transcripts levels of transcription factors controlling fatty acids synthesis; (2) TAG accumulation is limited by the activity of lipases/hydrolases that hydrolyze TAG pool supported by the increase in free fatty acids and monoacylglycerols. This comparative transcriptomics and metabolomics approach is useful in understanding the regulation of TAG biosynthesis, identifying bottlenecks, and the corresponding genes controlling these pathways identified as limitations, for generating Camelina varieties with improved seed and oil yields.

An integrated and comparative approach towards identification, characterization and functional annotation of candidate genes for drought tolerance in sorghum (Sorghum bicolor (L.) Moench)

BACKGROUND

Drought is the most disastrous abiotic stress that severely affects agricultural productivity worldwide. Understanding the biological basis of drought-regulated traits, requires identification and an in-depth characterization of genetic determinants using model organisms and high-throughput technologies. However, studies on drought tolerance have generally been limited to traditional candidate gene approach that targets only a single gene in a pathway that is related to a trait. In this study, we used sorghum, one of the model crops that is well adapted to arid regions, to mine genes and define determinants for drought tolerance using drought expression libraries and RNA-seq data.

RESULTS

We provide an integrated and comparative in silico candidate gene identification, characterization and annotation approach, with an emphasis on genes playing a prominent role in conferring drought tolerance in sorghum. A total of 470 non-redundant functionally annotated drought responsive genes (DRGs) were identified using experimental data from drought responses by employing pairwise sequence similarity searches, pathway and interpro-domain analysis, expression profiling and orthology relation. Comparison of the genomic locations between these genes and sorghum quantitative trait loci (QTLs) showed that 40% of these genes were co-localized with QTLs known for drought tolerance. The genome reannotation conducted using the Program to Assemble Spliced Alignment (PASA), resulted in 9.6% of existing single gene models being updated. In addition, 210 putative novel genes were identified using AUGUSTUS and PASA based analysis on expression dataset. Among these, 50% were single exonic, 69.5% represented drought responsive and 5.7% were complete gene structure models. Analysis of biochemical metabolism revealed 14 metabolic pathways that are related to drought tolerance and also had a strong biological network, among categories of genes involved. Identification of these pathways, signifies the interplay of biochemical reactions that make up the metabolic network, constituting fundamental interface for sorghum defence mechanism against drought stress.

CONCLUSIONS

This study suggests untapped natural variability in sorghum that could be used for developing drought tolerance. The data presented here, may be regarded as an initial reference point in functional and comparative genomics in the Gramineae family.

A novel bi-domain plant defensin MtDef5 with potent broad-spectrum antifungal activity binds to multiple phospholipids and forms oligomers

Defensins are cysteine-rich cationic antimicrobial peptides contributing to the innate immunity in plants. A unique gene encoding a highly cationic bi-domain defensin MtDef5 has been identified in a model legume Medicago truncatula. MtDef5 consists of two defensin domains of 50 amino acids each linked by a 7-amino acid peptide. It exhibits broad-spectrum antifungal activity against filamentous fungi at submicromolar concentrations. It rapidly permeabilizes the plasma membrane of the ascomycete fungi Fusarium graminearum and Neurospora crassa and induces accumulation of reactive oxygen species. It is internalized by these fungi, but uses spatially distinct modes of entry into these fungi. It co-localizes with cellular membranes, travels to nucleus and becomes dispersed in other subcellular locations. It binds to several membrane-resident phospholipids with preference for phosphatidylinositol monophosphates and forms oligomers. Mutations of the cationic amino acids present in the two γ-core motifs of this defensin that eliminate oligomerization also knockout its ability to induce membrane permeabilization and fungal growth arrest. MtDef5 is the first bi-domain plant defensin that exhibits potent broad-spectrum antifungal activity, recruits multiple membrane phospholipids and forms oligomers in their presence. These findings raise the possibility that MtDef5 might be useful as a novel antifungal agent in transgenic crops.

Prokaryotic expression and action mechanism of antimicrobial LsGRP1C recombinant protein containing a fusion partner of small ubiquitin-like modifier

Antimicrobial peptides (AMPs) are peptides exhibiting broad-spectrum antimicrobial activities and considered as potential therapeutic agents. LsGRP1^C, a novel AMP derived from defense-related LsGRP1 protein of Lilium, was proven to inhibit kinds of bacteria and fungi via alteration of microbial membrane permeability and induction of fungal programmed cell death-like phenomena by in vitro assays using synthetic LsGRP1^C. In this study, the prokaryotic production of LsGRP1^C recombinant protein containing an N-terminal fusion partner of the yeast small ubiquitin-like modifier (SUMO) was achieved by using optimized Escherichia coli host and purification buffer system, which lead to a high yield of soluble SUMO-LsGRP1^C fusion protein. In vitro assay revealed that E. coli-expressed SUMO-LsGRP1^C exhibited even better antifungal activity as compared to synthetic LsGRP1^C. Meanwhile, the ability of SUMO-LsGRP1^C in conducting fungal membrane permeabilization and programmed cell death was verified by SYTOX Green staining and 4',6-diamidino-2-phenylindole staining/terminal deoxynucleotidyl transferase dUTP nick-end labeling assays, respectively, indicating that E. coli-expressed SUMO-LsGRP1^C shares identical modes of action with synthetic LsGRP1^C. Herein, this E. coli expression system enables the effective and convenient production of antimicrobial LsGRP1^C in a form of SUMO-fused recombinant protein.

Natural Antimicrobial Peptides as Inspiration for Design of a New Generation Antifungal Compounds

Invasive fungal infections are associated with high mortality rates, despite appropriate antifungal therapy. Limited therapeutic options, resistance development and the high mortality of invasive fungal infections brought about more concern triggering the search for new compounds capable of interfering with fungal viability and virulence. In this context, peptides gained attention as promising candidates for the antimycotics development. Variety of structural and functional characteristics identified for various natural antifungal peptides makes them excellent starting points for design novel drug candidates. Current review provides a brief overview of natural and synthetic antifungal peptides.

Evaluation of the antimicrobial activities of ultrasonicated spinach leaf extracts using RAPD markers and electron microscopy

Spinach (Spinacia oleracea L.) leaves represent an important dietary source of nutrients, antioxidants and antimicrobials. As such, spinach leaves play an important role in health and have been used in the treatment of human diseases since ancient times. Here, the aims were to optimize the extraction methods for recovering antimicrobial substances of spinach leaves, determine the minimum inhibitory concentrations (MICs) of the antimicrobial substances against Escherichia coli and Staphylococcus aureus and, finally, evaluate the effects of spinach leaves' antimicrobials on bacterial DNA using central composite face-centered methods. The effect of the extracts on both Gram-positive and Gram-negative bacterial models was examined by scanning electron microscopy (SEM) and random amplification of polymorphic (bacterial) DNA (RAPD). The optimal extraction conditions were at 45 °C, ultrasound power of 44% and an extraction time of 23 min. The spinach extracts exhibited antimicrobial activities against both bacteria with MICs in the 60-100 mg/ml range. Interestingly, SEM showed that the treated bacterial cells appear damaged with a reduction in cell number. RAPD analysis of genomic DNA showed that the number and sizes of amplicons were decreased by treatments. Based on these results, it was inferred that spinach leaf extracts exert bactericidal activities by both inducing mutations in DNA and causing cell wall disruptions.

Comprehensive study of excess phosphate response reveals ethylene mediated signaling that negatively regulates plant growth and development

Excess Phosphorus (P) in agriculture is causing serious environmental problems like eutrophication of lakes and rivers. Unlike the enormous information available for phosphate starvation response (P₀), very few information is available for the effect of excess phosphate P_i on plants. Characterization of Excess Phosphate Response (EP_iR) is essential for designing strategies to increase phosphate accumulation and tolerance. We show a significant modulation in the root developmental plasticity under the increasing supply of excess P_i. An excess supply of 20 mM P_i (P₂₀) produces a shallow root system architecture (RSA), reduces primary root growth, root apical meristem size, and meristematic activity in Arabidopsis. The inhibition of primary root growth and development is indeterminate in nature and caused by the decrease in number of meristematic cortical cells due to EP_iR. Significant changes occurred in metal nutrients level due to excess P_i supply. A comparative microarray investigation of the EP_iR response reveals a modulation in ethylene biosynthesis and signaling, metal ions deficiency response, and root development related genes. We used ethylene-insensitive or sensitive mutants to provide more evidence for ethylene-mediated signaling. A new role of EP_iR in regulating the developmental responses of plants mediated by ethylene has been demonstrated.

Defense-related proteins involved in sugarcane responses to biotic stress

Sugarcane is one of the most important agricultural crops in the world. However, pathogen infection and herbivore attack cause constant losses in yield. Plants respond to pathogen infection by inducing the expression of several protein types, such as glucanases, chitinases, thaumatins, peptidase inhibitors, defensins, catalases and glycoproteins. Proteins induced by pathogenesis are directly or indirectly involved in plant defense, leading to pathogen death or inducing other plant defense responses. Several of these proteins are induced in sugarcane by different pathogens or insects and have antifungal or insecticidal activity. In this review, defense-related proteins in sugarcane are described, with their putative mechanisms of action, pathogen targets and biotechnological perspectives.

Antimicrobial Peptides from Fruits and Their Potential Use as Biotechnological Tools-A Review and Outlook

Bacterial resistance is a major threat to plant crops, animals and human health, and over the years this situation has increasingly spread worldwide. Due to their many bioactive compounds, plants are promising sources of antimicrobial compounds that can potentially be used in the treatment of infections caused by microorganisms. As well as stem, flowers and leaves, fruits have an efficient defense mechanism against pests and pathogens, besides presenting nutritional and functional properties due to their multifunctional molecules. Among such compounds, the antimicrobial peptides (AMPs) feature different antimicrobials that are capable of disrupting the microbial membrane and of acting in binding to intra-cytoplasmic targets of microorganisms. They are therefore capable of controlling or halting the growth of microorganisms. In summary, this review describes the major classes of AMPs found in fruits, their possible use as biotechnological tools and prospects for the pharmaceutical industry and agribusiness.

Evolution of the defensin-like gene family in grass genomes

Plant defensins are small, diverse, cysteine-rich peptides, belonging to a group of pathogenesis-related defense mechanism proteins, which can provide a barrier against a broad range of pathogens. In this study, 51 defensin-like (DEFL) genes in Gramineae, including brachypodium, rice, maize and sorghum were identified based on bioinformatics methods. Using the synteny analysis method, we found that 21 DEFL genes formed 30 pairs of duplicated blocks that have undergone large-scale duplication events, mostly occurring between species. In particular, some chromosomal regions are highly conserved in the four grasses. Using mean Ks values, we estimated the approximate time of divergence for each pair of duplicated regions and found that these regions generally diverged more than 40 million years ago (Mya). Selection pressure analysis showed that the DEFL gene family is subjected to purifying selection. However, sliding window analysis detected partial reg ions of duplicated genes under positive selection. The evolutionary patterns within DEFL gene families among grasses can be used to explore the subsequent functional divergence of duplicated genes and to further analyse the antimicrobial effects of defensins during plant development.

Defense peptide repertoire of Stellaria media predicted by high throughput next generation sequencing

Being perfectly adapted to diverse environments, chickweed (Stellaria media (L.) Vill), a ubiquitous garden weed, grows widely in Europe and North America. As opposed to the model plants, many weeds, and S. media in particular, have been poorly studied, although they are likely to contain promising components of immunity and novel resistance genes. In this study, for the first time RNA-seq analysis of healthy and infected with Fusarium oxysporum chickweed seedlings, as well as de novo transcriptome assembly and annotation, are presented. Note, this research is focused on antimicrobial peptides (AMPs), the major components of plant immune system. Using custom software developed earlier, 145 unique putative AMPs (pAMPs) including defensins, thionins, hevein-like peptides, snakins, alpha-hairpinins, LTPs, and cysteine-rich peptides with novel cysteine motifs were predicted. Furthermore, changes in AMP expression profile in response to fungal infection were traced. In addition, the comparison of chickweed AMP repertoire with those of other Caryophyllaceae plants whose transcriptomes are presently available is made. As a result, alpha-hairpinins and hevein-like peptides which display characteristic modular structure appear to be specific AMPs distinguishing S. media from Dianthus caryophyllus, Silene vulgaris, and Silene latifolia. Finally, revealing several AMPs with proven antimicrobial activity gives opportunity to conclude that the presented method of AMP repertoire analysis reveals highly active AMPs playing vital role in plant immunity.

Barley Stripe Rust Resistance QTL: Development and Validation of SNP Markers for Resistance to Puccinia striiformis f. sp. hordei

Quantitative trait loci (QTL) for barley stripe rust resistance were mapped in recombinant inbred lines (RIL) from a 'Lenetah' × 'Grannelose Zweizeilige' (GZ) cross. GZ is known for a major seedling resistance QTL on chromosome 4H but linked markers suitable for marker-assisted selection have not been developed. This study identified the 4H QTL (log of the likelihood [LOD] = 15.94 at 97.19 centimorgans [cM]), and additional QTL on chromosomes 4H and 6H (LOD = 5.39 at 72.7 cM and 4.24 at 34.46 cM, respectively). A QTL on chromosome 7H (LOD = 2.04 at 81.07 cM) was suggested. All resistance alleles were derived from GZ. Evaluations of adult plant response in Corvallis, OR in 2013 and 2015 provided evidence of QTL at the same positions. However, the minor QTL on 4H was not statistically significant in either location/year, while the 7H QTL was significant in both. The single-nucleotide polymorphism markers flanking the resistance QTL were validated in RIL from a '95SR316A' × GZ cross for their ability to predict seedling resistance. In 95SR316A × GZ, 91 to 92% of RIL with GZ alleles at the major 4H QTL and at least one other were resistant to moderate in reaction. In these populations, at least two QTL were required to transfer the barley stripe rust resistance from GZ.

Interaction between the plant ApDef1 defensin and Saccharomyces cerevisiae results in yeast death through a cell cycle- and caspase-dependent process occurring via uncontrolled oxidative stress

BACKGROUND

Plant defensins were discovered at beginning of the 90s'; however, their precise mechanism of action is still unknown. Herein, we studied ApDef₁-Saccharomyces cerevisiae interaction.

METHODS

ApDef₁-S. cerevisiae interaction was studied by determining the MIC, viability and death kinetic assays. Viability assay was repeated with hydroxyurea synchronized-yeast and pretreated with CCCP. Plasma membrane permeabilization, ROS induction, chromatin condensation, and caspase activation analyses were assessed through Sytox green, DAB, DAPI and FITC-VAD-FMK, respectively. Viability assay was done in presence of ascorbic acid and Z-VAD-FMK. Ultrastructural analysis was done by electron microscopy.

RESULTS

ApDef₁ caused S. cerevisiae cell death and MIC was 7.8μM. Whole cell population died after 18h of ApDef₁ interaction. After 3h, 98.76% of synchronized cell population died. Pretreatment with CCCP protected yeast from ApDef₁ induced death. ApDef₁-S. cerevisiae interaction resulted in membrane permeabilization, H₂O₂ increased production, chromatin condensation and caspase activation. Ascorbic acid prevented yeast cell death and membrane permeabilization. Z-VAD-FMK prevented yeast cell death.

CONCLUSIONS

ApDef₁-S. cerevisiae interaction caused cell death through cell cycle dependentprocess which requires preserved membrane potential. After interaction, yeast went through uncontrolled ROS production and accumulation, which led to plasma membrane permeabilization, chromatin condensation and, ultimately, cell death by activation of caspase-dependent apoptosis via.

GENERAL SIGNIFICANCE

We show novel requirements for the interaction between plant defensin and fungi cells, i.e. cell cycle phase and membrane potential, and we indicate that membrane permeabilization is probably caused by ROS and therefore, it would be an indirect event of the ApDef₁-S. cerevisiae interaction.

Genome Wide Identification and Functional Prediction of Long Non-Coding RNAs Responsive to Sclerotinia sclerotiorum Infection in Brassica napus

Sclerotinia stem rot caused by Sclerotinia sclerotiorum affects canola production worldwide. Emerging evidence suggests that long non-coding RNAs (lncRNAs) play important roles in the regulation of gene expression in plants, in response to both abiotic and biotic stress. So far, identification of lncRNAs has been limited to a few model plant species, and their roles in mediating responses to biotic stresses are yet to be characterized in Brassica napus. The present study reports the identification of novel lncRNAs responsive to S. sclerotiorum infection in B. napus at two time points after infection (24 hpi and 48 hpi) using a stranded RNA-Sequencing technique and a detection pipeline for lncRNAs. Of the total 3,181 lncRNA candidates, 2,821 lncRNAs were intergenic, 111 were natural antisense transcripts, 76 possessed exonic overlap with the reference coding transcripts while the remaining 173 represented novel lnc- isoforms. Forty one lncRNAs were identified as the precursors for microRNAs (miRNAs) including miR156, miR169 and miR394, with significant roles in mediating plant responses to fungal phytopathogens. A total of 931 differentially expressed lncRNAs were identified in response to S. sclerotiorum infection and the expression of 12 such lncRNAs was further validated using qRT-PCR. B. napus antisense lncRNA, TCONS_00000966, having 90% overlap with a plant defensin gene, showed significant induction at both infection stages, suggesting its involvement in the transcriptional regulation of defense responsive genes under S. sclerotiorum infection. Additionally, nine lncRNAs showed overlap with cis-regulatory regions of differentially expressed genes of B. napus. Quantitative RT-PCR verification of a set of S. sclerotiorum responsive sense/antisense transcript pairs revealed contrasting expression patterns, supporting the hypothesis that steric clashes of transcriptional machinery may lead to inactivation of sense promoter. Our findings highlight the potential contributions of lncRNAs in regulating expression of plant genes that respond to biotic stress.

Theobroma cacao L. pathogenesis-related gene tandem array members show diverse expression dynamics in response to pathogen colonization

Background

The pathogenesis-related (PR) group of proteins are operationally defined as polypeptides that increase in concentration in plant tissues upon contact with a pathogen. To date, 17 classes of highly divergent proteins have been described that act through multiple mechanisms of pathogen resistance. Characterizing these families in cacao, an economically important tree crop, and comparing the families to those in other species, is an important step in understanding cacao’s immune response.

Results

Using publically available resources, all members of the 17 recognized pathogenesis-related gene families in the genome of Theobroma cacao were identified and annotated resulting in a set of ~350 members in both published cacao genomes. Approximately 50 % of these genes are organized in tandem arrays scattered throughout the genome. This feature was observed in five additional plant taxa (three dicots and two monocots), suggesting that tandem duplication has played an important role in the evolution of the PR genes in higher plants. Expression profiling captured the dynamics and complexity of PR genes expression at basal levels and after induction by two cacao pathogens (the oomycete, Phytophthora palmivora, and the fungus, Colletotrichum theobromicola), identifying specific genes within families that are more responsive to pathogen challenge. Subsequent qRT-PCR validated the induction of several PR-1, PR-3, PR-4, and PR-10 family members, with greater than 1000 fold induction detected for specific genes.

Conclusions

We describe candidate genes that are likely to be involved in cacao’s defense against Phytophthora and Colletotrichum infection and could be potentially useful for marker-assisted selection for breeding of disease resistant cacao varieties. The data presented here, along with existing cacao—omics resources, will enable targeted functional genetic screening of defense genes likely to play critical functions in cacao’s defense against its pathogens.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2693-3) contains supplementary material, which is available to authorized users.

Integrating transcriptomics and metabolomics to characterise the response of Astragalus membranaceus Bge. var. mongolicus (Bge.) to progressive drought stress

BACKGROUND

Astragalus membranaceus Bge. var. mongolicus (Bge.) Hsiao (A. mongolicus) is an important traditional Chinese herb that is cultivated on a large scale in northwestern China. Understanding plant responses to drought has important effects on ecological environment recovery and local economic development. Here, we combined transcriptomics (Illumina Hiseq 2000) and metabolomics ((1)H-NMR) to investigate how the roots of two-year-old A. mongolicus responded to 14 days of progressive drought stress.

RESULTS

The dried soil reduced the relative water content (RWC) of the leaves and biomass, induced the differential expression of a large fraction of the transcriptome and significantly altered the metabolic processes. PCA analysis demonstrated that the sucrose, proline, and malate metabolites contributed greatly to the separation. Strikingly, proline was increased by almost 60-fold under severe stress compared to the control. Some backbone pathways, including glycolysis, tricarboxylic acid (TCA) cycle, glutamate-mediated proline biosynthesis, aspartate family metabolism and starch and sucrose metabolism, were significantly affected by drought. An integrated analysis of the interaction between key genes and the altered metabolites involved in these pathways was performed.

CONCLUSIONS

Our findings demonstrated that the expression of drought-responsive genes showed a strong stress-dose dependency. Analysis of backbone pathways of the transcriptome and metabolome revealed specific genotypic responses to different levels of drought. The variation in molecular strategies to the drought may play an important role in how A. mongolicus and other legume crops adapt to drought stress.

Emerging Agricultural Biotechnologies for Sustainable Agriculture and Food Security

As global populations continue to increase, agricultural productivity will be challenged to keep pace without overtaxing important environmental resources. A dynamic and integrated approach will be required to solve global food insecurity and position agriculture on a trajectory toward sustainability. Genetically modified (GM) crops enhanced through modern biotechnology represent an important set of tools that can promote sustainable agriculture and improve food security. Several emerging biotechnology approaches were discussed in a recent symposium organized at the 13th IUPAC International Congress of Pesticide Chemistry meeting in San Francisco, CA, USA. This paper summarizes the innovative research and several of the new and emerging technologies within the field of agricultural biotechnology that were presented during the symposium. This discussion highlights how agricultural biotechnology fits within the context of sustainable agriculture and improved food security and can be used in support of further development and adoption of beneficial GM crops.

Expression profiles of defence related cDNAs in oil palm (Elaeis guineensis Jacq.) inoculated with mycorrhizae and Trichoderma harzianum Rifai T32

Basal stem rot is one of the major diseases of oil palm (Elaies guineensis Jacq.) caused by pathogenic Ganoderma species. Trichoderma and mycorrhizae were proposed to be able to reduce the disease severity. However, their roles in improving oil palm defence system by possibly inducing defence-related genes in the host are not well characterized. To better understand that, transcript profiles of eleven putative defence-related cDNAs in the roots of oil palm inoculated with Trichoderma harzianum T32 and mycorrhizae at different time points were studied. Transcripts encoding putative Bowman-Birk protease inhibitor (EgBBI2) and defensin (EgDFS) increased more than 2 fold in mycorrhizae-treated roots at 6 weeks post inoculation (wpi) compared to those in controls. Transcripts encoding putative dehydrin (EgDHN), glycine-rich RNA binding protein (EgGRRBP), isoflavone reductase (EgIFR), type 2 ribosome inactivating protein (EgT2RIP), and EgDFS increased in the oil palm roots treated with T. harzianum at 6 and/or 12 wpi compared to those in the controls. Some of these genes were also expressed in oil palm roots treated with Ganoderma boninense. This study provides an insight of some defence-related genes induced by Trichoderma and mycorrhizae, and their roles as potential agents to boost the plant defence system.

Cysteine-stabilized αβ defensins: From a common fold to antibacterial activity

Antimicrobial peptides (AMPs) seem to be promising alternatives to common antibiotics, which are facing increasing bacterial resistance. Among them are the cysteine-stabilized αβ defensins. These peptides are small, with a length ranging from 34 to 54 amino acid residues, cysteine-rich and extremely stable, normally composed of an α-helix and three β-strands stabilized by three or four disulfide bonds and commonly found in several organisms. Moreover, animal and plant CSαβ defensins present different specificities, the first being mainly active against bacteria and the second against fungi. The role of the CSαβ-motif remains unknown, but a common antibacterial mechanism of action, based on the inhibition of the cell-wall formation, has already been observed in some fungal and invertebrate defensins. In this context, the present work aims to group the data about CSαβ defensins, highlighting their evolution, conservation, structural characteristics, antibacterial activity and biotechnological perspectives.

Predicting the Minimal Inhibitory Concentration for Antimicrobial Peptides with Rana-Box Domain

The global spreading of multidrug resistance has motivated the search for new antibiotic classes including different types of antimicrobial peptides (AMPs). Computational methods for predicting activity in terms of the minimal inhibitory concentration (MIC) of AMPs can facilitate "in silico" design and reduce the cost of synthesis and testing. We have used an original method for separating training and test data sets, both of which contain the sequences and measured MIC values of non-homologous anuran peptides having the Rana-box disulfide motif at their C-terminus. Using a more flexible profiling methodology (sideways asymmetry moment, SAM) than the standard hydrophobic moment, we have developed a two-descriptor model to predict the bacteriostatic activity of Rana-box peptides against Gram-negative bacteria--the first multilinear quantitative structure-activity relationship model capable of predicting MIC values for AMPs of widely different lengths and low identity using such a small number of descriptors. Maximal values for SAMs, as defined and calculated in our method, furthermore offer new structural insight into how different segments of a peptide contribute to its bacteriostatic activity, and this work lays the foundations for the design of active artificial AMPs with this type of disulfide bridge.

Toxic proteins in plants

Plants have evolved to synthesize a variety of noxious compounds to cope with unfavorable circumstances, among which a large group of toxic proteins that play a critical role in plant defense against predators and microbes. Up to now, a wide range of harmful proteins have been discovered in different plants, including lectins, ribosome-inactivating proteins, protease inhibitors, ureases, arcelins, antimicrobial peptides and pore-forming toxins. To fulfill their role in plant defense, these proteins exhibit various degrees of toxicity towards animals, insects, bacteria or fungi. Numerous studies have been carried out to investigate the toxic effects and mode of action of these plant proteins in order to explore their possible applications. Indeed, because of their biological activities, toxic plant proteins are also considered as potentially useful tools in crop protection and in biomedical applications, such as cancer treatment. Genes encoding toxic plant proteins have been introduced into crop genomes using genetic engineering technology in order to increase the plant's resistance against pathogens and diseases. Despite the availability of ample information on toxic plant proteins, very few publications have attempted to summarize the research progress made during the last decades. This review focuses on the diversity of toxic plant proteins in view of their toxicity as well as their mode of action. Furthermore, an outlook towards the biological role(s) of these proteins and their potential applications is discussed.