Investigation of Antimicrobial Peptide Genes Associated with Fungus and Insect Resistance in Maize

Recent approaches in the application of antimicrobial peptides in food preservation

Antimicrobial peptides (AMPs) are small peptides existing in nature as an important part of the innate immune system in various organisms. Notably, the AMPs exhibit inhibitory effects against a wide spectrum of pathogens, showcasing potential applications in different fields such as food, agriculture, medicine. This review explores the application of AMPs in the food industry, emphasizing their crucial role in enhancing the safety and shelf life of food and how they offer a viable substitute for chemical preservatives with their biocompatible and natural attributes. It provides an overview of the recent advancements, ranging from conventional approaches of using natural AMPs derived from bacteria or other sources to the biocomputational design and usage of synthetic AMPs for food preservation. Recent innovations such as structural modifications of AMPs to improve safety and suitability as food preservatives have been discussed. Furthermore, the active packaging and creative fabrication strategies such as nano-formulation, biopolymeric peptides and casting films, for optimizing the efficacy and stability of these peptides in food systems are summarized. The overall focus is on the spectrum of applications, with special attention to potential challenges in the usage of AMPs in the food industry and strategies for their mitigation.

The Roadmap of Plant Antimicrobial Peptides Under Environmental Stress: From Farm to Bedside

Antimicrobial peptides (AMPs) are the most favorable alternatives in overcoming multidrug resistance, alone or synergistically with conventional antibiotics. Plant-derived AMPs, as cysteine-rich peptides, widely compensate the pharmacokinetic drawbacks of peptide therapeutics. Compared to the putative genes encrypted in the genome, AMPs that are produced under stress are active forms with the ability to combat resistant microbial species. Within this study, plant-derived AMPs, namely, defensins, nodule-specific cysteine-rich peptides, snakins, lipid transfer proteins, hevein-like proteins, α-hairpinins, and aracins, expressed under biotic and abiotic stresses, are classified. We could observe that while α-hairpinins and snakins display a helix-turn-helix structure, conserved motif patterns such as β1αβ2β3 and β1β2β3 exist in plant defensins and hevein-like proteins, respectively. According to the co-expression data, several plant AMPs are expressed together to trigger synergistic effects with membrane disruption mechanisms such as toroidal pore, barrel-stave, and carpet models. The application of AMPs as an eco-friendly strategy in maintaining agricultural productivity through the development of transgenes and bio-pesticides is discussed. These AMPs can be consumed in packaging material, wound-dressing products, coating catheters, implants, and allergology. AMPs with cell-penetrating properties are verified for the clearance of intracellular pathogens. Finally, the dominant pharmacological activities of bioactive peptides derived from the gastrointestinal digestion of plant AMPs, namely, inhibitors of renin and angiotensin-converting enzymes, dipeptidyl peptidase IV and α-glucosidase inhibitors, antioxidants, anti-inflammatory, immunomodulating, and hypolipidemic peptides, are analyzed. Conclusively, as phytopathogens and human pathogens can be affected by plant-derived AMPs, they provide a bright perspective in agriculture, breeding, food, cosmetics, and pharmaceutical industries, translated as farm to bedside.

Identification of potato Lipid transfer protein gene family and expression verification of drought genes StLTP1 and StLTP7

Lipid transfer proteins (LTPs) are widely distributed in plants and play an important role in the response to stress. Potato (Solanum tuberosum L.) is sensitive to a lack of water, and drought stress is one of the limiting factors for its yield. Therefore, mining candidate functional genes for drought stress and creating new types of potato germplasm for drought resistance is an effective way to solve this problem. There are few reports on the LTP family in potato. In this study, 39 members of the potato LTP family were identified. They were located on seven chromosomes, and the amino acid sequences encoded ranged from 101 to 345 aa. All 39 family members contained introns and had exons that ranged from one to four. Conserved motif analysis of potato LTP transcription factors showed that 34 transcription factors contained Motif 2 and Motif 4, suggesting that they were conserved motifs of potato LTP. Compared with the LTP genes of homologous crops, the potato and tomato (Solanum lycopersicum L.) LTPs were the mostly closely related. The StLTP1 and StLTP7 genes were screened by quantitative reverse transcription PCR combined with potato transcriptome data to study their expression in tissues and the characteristics of their responses to drought stress. The results showed that StLTP1 and StLTP7 were upregulated in the roots, stems, and leaves after PEG 6000 stress. Taken together, our study provides comprehensive information on the potato LTP family that will help to develop a framework for further functional studies.

Structural Analysis and Antimicrobial Mechanism of a Protein GBSPI-A from Ginkgo Biloba Seed

Ginkgo biloba seed has antimicrobial activity. In this study, ginkgo biloba seed protein was prepared, identified, and named GBSPI-A, finding its construction was similar to 11-S globulin. Then, the influence of GBSPI-A on the cell membrane and physiological metabolism of K. pneumoniae and S. aureus were investigated. The results showed that GBSPI-A (20 mg/mL) destroyed the cell membrane, causing leakage of intracellular material and inhibited bacterial growth with an inhibition rate of approximately 80%. In addition, the GBSPI-A (10 mg/mL) caused the decreasing activity of ATPase and respiratory rate, and the respiratory depression rate was 7.24%. Furthermore, the decreasing ATP synthesis and intracellular β-galactosidase activity led to an insufficient supply of physiological metabolic energy. Therefore, the results showed that GBSPI-A could be used as a natural bacteriostatic agent to replace related drugs and also provide a new insight into the application of GBSPI-A in food safety.

Plant Antimicrobial Peptides (PAMPs): Features, Applications, Production, Expression, and Challenges

The quest for an extraordinary array of defense strategies is imperative to reduce the challenges of microbial attacks on plants and animals. Plant antimicrobial peptides (PAMPs) are a subset of antimicrobial peptides (AMPs). PAMPs elicit defense against microbial attacks and prevent drug resistance of pathogens given their wide spectrum activity, excellent structural stability, and diverse mechanism of action. This review aimed to identify the applications, features, production, expression, and challenges of PAMPs using its structure-activity relationship. The discovery techniques used to identify these peptides were also explored to provide insight into their significance in genomics, transcriptomics, proteomics, and their expression against disease-causing pathogens. This review creates awareness for PAMPs as potential therapeutic agents in the medical and pharmaceutical fields, such as the sensitive treatment of bacterial and fungal diseases and others and their utilization in preserving crops using available transgenic methods in the agronomical field. PAMPs are also safe to handle and are easy to recycle with the use of proteases to convert them into more potent antimicrobial agents for sustainable development.

Lipid tails modulate antimicrobial peptide membrane incorporation and activity

Membrane disrupting antimicrobial peptides (AMPs) are often amphipathic peptides that interact directly with lipid bilayers. AMPs are generally thought to interact mostly with lipid head groups, but it is less clear how the lipid alkyl chain length and saturation modulate interactions with membranes. Here, we used native mass spectrometry to measure the stoichiometry of three different AMPs-LL-37, indolicidin, and magainin-2-in lipid nanodiscs. We also measured the activity of these AMPs in unilamellar vesicle leakage assays. We found that LL-37 formed specific hexamer complexes but with different intermediates and affinities that depended on the bilayer thickness. LL-37 was also most active in lipid bilayers containing longer, unsaturated lipids. In contrast, indolicidin incorporated to a higher degree into more fluid lipid bilayers but was more active with bilayers with thinner, less fluid lipids. Finally, magainin-2 incorporated to a higher degree into bilayers with longer, unsaturated alkyl chains and showed more activity in these same conditions. Together, these data show that higher amounts of peptide incorporation generally led to higher activity and that AMPs tend to incorporate more into longer unsaturated lipid bilayers. However, the activity of AMPs was not always directly related to amount of peptide incorporated.

Unraveling Microbial Volatile Elicitors Using a Transparent Methodology for Induction of Systemic Resistance and Regulation of Antioxidant Genes at Expression Levels in Chili against Bacterial Wilt Disease

Microbial volatiles benefit the agricultural ecological system by promoting plant growth and systemic resistance against diseases without harming the environment. To explore the plant growth-promoting efficiency of VOCs produced by Pseudomonas fluorescens PDS1 and Bacillus subtilis KA9 in terms of chili plant growth and its biocontrol efficiency against Ralstonia solanacearum, experiments were conducted both in vitro and in vivo. A closure assembly was designed using a half-inverted plastic bottle to demonstrate plant–microbial interactions via volatile compounds. The most common volatile organic compounds were identified and reported; they promoted plant development and induced systemic resistance (ISR) against wilt pathogen R. solanacearum. The PDS1 and KA9 VOCs significantly increased defensive enzyme activity and overexpressed the antioxidant genes PAL, POD, SOD, WRKYa, PAL1, DEF-1, CAT-2, WRKY40, HSFC1, LOX2, and NPR1 related to plant defense. The overall gene expression was greater in root tissue as compared to leaf tissue in chili plant. Our findings shed light on the relationship among rhizobacteria, pathogen, and host plants, resulting in plant growth promotion, disease suppression, systemic resistance-inducing potential, and antioxidant response with related gene expression in the leaf and root tissue of chili.

Plant Antimicrobial Peptides as Potential Tool for Topic Treatment of Hidradenitis Suppurativa

Among chronic skin autoinflammatory diseases, Hidradenitis Suppurativa (HS) stands out for its chronicity, highly variable condition, and profound impact on the patients' quality of life. HS is characterized by suppurative skin lesions in diverse body areas, including deep-seated painful nodules, abscesses, draining sinus, and bridged scars, among others, with typical topography. To date, HS is considered a refractory disease and medical treatments aim to reduce the incidence, the infection, and the pain of the lesions. For this purpose, different classes of drugs, including anti-inflammatory molecules, antibiotics and biological drugs are being used. Antimicrobial peptides (AMPs), also called defense peptides, emerge as a new class of therapeutic compounds, with broad-spectrum antimicrobial action, in addition to reports on their anti-inflammatory, healing, and immunomodulating activity. Such peptides are present in prokaryotes and eukaryotes, as part of the innate eukaryotic immune system. It has been proposed that a deregulation in the expression of AMPs in human epithelial tissues of HS patients may be associated with the etiology of this skin disease. In this scenario, plant AMPs stand out for their richness, diversity of types, and broad antimicrobial effects, with potential application for topical systemic use in patients affected by HS.

Lipid Transfer Proteins (LTPs)-Structure, Diversity and Roles beyond Antimicrobial Activity

Lipid transfer proteins (LTPs) are among the most promising plant-exclusive antimicrobial peptides (AMPs). They figure among the most challenging AMPs from the point of view of their structural diversity, functions and biotechnological applications. This review presents a current picture of the LTP research, addressing not only their structural, evolutionary and further predicted functional aspects. Traditionally, LTPs have been identified by their direct isolation by biochemical techniques, whereas omics data and bioinformatics deserve special attention for their potential to bring new insights. In this context, new possible functions have been identified revealing that LTPs are actually multipurpose, with many additional predicted roles. Despite some challenges due to the toxicity and allergenicity of LTPs, a systematic review and search in patent databases, indicate promising perspectives for the biotechnological use of LTPs in human health and also plant defense.

A sugarcane mosaic virus vector for rapid in planta screening of proteins that inhibit the growth of insect herbivores

Spodoptera frugiperda (fall armyworm) is a notorious pest that threatens maize production worldwide. Current control measures involve the use of chemical insecticides and transgenic maize expressing Bacillus thuringiensis (Bt) toxins. Although additional transgenes have confirmed insecticidal activity, limited research has been conducted in maize, at least partially due to the technical difficulty of maize transformation. Here, we describe implementation of a sugarcane mosaic virus (SCMV) vector for rapidly testing the efficacy of both endogenous maize genes and heterologous genes from other organisms for the control of S. frugiperda in maize. Four categories of proteins were tested using the SCMV vector: (i) maize defence signalling proteins: peptide elicitors (Pep1 and Pep3) and jasmonate acid conjugating enzymes (JAR1a and JAR1b); (ii) maize defensive proteins: the previously identified ribosome-inactivating protein (RIP2) and maize proteinase inhibitor (MPI), and two proteins with predicted but unconfirmed anti-insect activities, an antimicrobial peptide (AMP) and a lectin (JAC1); (iii) lectins from other plant species: Allium cepa agglutinin (ACA) and Galanthus nivalis agglutinin (GNA); and (iv) scorpion and spider toxins: peptides from Urodacus yaschenkoi (UyCT3 and UyCT5) and Hadronyche versuta (Hvt). In most cases, S. frugiperda larval growth was reduced by transient SCMV-mediated overexpression of genes encoding these proteins. Additionally, experiments with a subset of the SCMV-expressed genes showed effectiveness against two aphid species, Rhopalosiphum maidis (corn leaf aphid) and Myzus persicae (green peach aphid). Together, these results demonstrate that SCMV vectors are a rapid screening method for testing the efficacy and insecticidal activity of candidate genes in maize.

Shared and tailored common bean transcriptomic responses to combined fusarium wilt and water deficit

Common bean (Phaseolus vulgaris L.), one of the most consumed food legumes worldwide, is threatened by two main constraints that are found frequently together in nature, water deficit (WD) and fusarium wilt (Fop). To understand the shared and unique responses of common bean to Fop and WD, we analyzed the transcriptomic changes and phenotypic responses in two accessions, one resistant and one susceptible to both stresses, exposed to single and combined stresses. Physiological responses (photosynthetic performance and pigments quantification) and disease progression were also assessed. The combined FopWD imposition negatively affected the photosynthetic performance and increased the susceptible accession disease symptoms. The susceptible accession revealed a higher level of transcriptional changes than the resistant one, and WD single stress triggered the highest transcriptional changes. While 89 differentially expressed genes were identified exclusively in combined stresses for the susceptible accession, 35 were identified in the resistant one. These genes belong mainly to "stress", "signaling", "cell wall", "hormone metabolism", and "secondary metabolism" functional categories. Among the up-regulated genes with higher expression in the resistant accession, the cysteine-rich secretory, antigen 5 and Pr-1 (CAP) superfamily protein, a ribulose bisphosphate carboxylase family protein, and a chitinase A seem promising targets for multiple stress breeding.

Plant antimicrobial peptides: structures, functions, and applications

Antimicrobial peptides (AMPs) are a class of short, usually positively charged polypeptides that exist in humans, animals, and plants. Considering the increasing number of drug-resistant pathogens, the antimicrobial activity of AMPs has attracted much attention. AMPs with broad-spectrum antimicrobial activity against many gram-positive bacteria, gram-negative bacteria, and fungi are an important defensive barrier against pathogens for many organisms. With continuing research, many other physiological functions of plant AMPs have been found in addition to their antimicrobial roles, such as regulating plant growth and development and treating many diseases with high efficacy. The potential applicability of plant AMPs in agricultural production, as food additives and disease treatments, has garnered much interest. This review focuses on the types of plant AMPs, their mechanisms of action, the parameters affecting the antimicrobial activities of AMPs, and their potential applications in agricultural production, the food industry, breeding industry, and medical field.

Antibacterial Activity of Tris NaCl and PBS Buffer Protein Extract of Cassia fistula, Saccharum officinarum, Albizia lebbeck and Cymbopogon citrates Against Bacterial Strains

Medicinal plants are gaining popularity over synthetic medicines because antibiotic resistance demands the alternative source of medication. In the present research, the crude protein extraction of 4 medicinal plants Cassia fistula, Saccharum officinarum, Albizia lebbeck and Cymbopogon citrates was carried out. Crude protein extraction was done by 2 different buffers i.e. Tris NaCl buffer and PBS buffer. Protein confirmation was done by Bradford assay in the spectrophotometer. Antibacterial potential was checked and compared against Escherichia coli, Bacillus subtilis, Neisseria gonorrhoea, Bacillus cereus and Proteus mirabilis. Antibacterial assay was performed by disc diffusion method, agar well method and zones of inhibition were calculated. The study results indicated that Tris NaCl extracts' antimicrobial potential is higher than that of the PBS buffer. On disc diffusion method the Tris NaCl buffer extracts of Cymbopogon citrates showed maximum zone of inhibition 11 mm and 9 mm against Bacillus subtilis and Bacillus cereus respectively and control chloramphenicol showed maximum zone of inhibition 26 mm against Bacillus subtilis. Cassia fistula showed maximum zone of inhibition of 7 mm against Bacillus cereus while Saccharum officinarum and Albizia lebbeck didn't show the any antibacterial activity. On the other hand, Protein extracts from PBS buffer didn't show zone of inhibition against any bacteria. Only Albizia lebbeck showed minute zone of inhibition against Neisseria gonorrhea. On well diffusion method, Cassia fistula Tris NaCl protein extract showed the maximum zone of inhibition 20 mm and 18 mm against Proteus mirabilis and Bacillus subtilis respectively. While Albizia lebbeck PBS protein extract showed the maximum zone of inhibition 19 mm and 17 mm against Bacillus subtilis and Bacillus cereus. The results revealed that the protein extract of Albizia lebbeck, Cymbopogon citrates and Cassia fistula can be used tosynthesize antimicrobial drugs to treat the bacterial infections.

Utilization of a recombinant defensin from Maize (Zea mays L.) as a potential antimicrobial peptide

The search for effective and bioactive antimicrobial molecules to  encounter the medical need for new antibiotics is an encouraging area of research. Plant defensins are small cationic, cysteine-rich peptides with a stabilized tertiary structure by disulfide-bridges and characterized by a wide range of biological functions. The heterologous expression of Egyptian maize defensin (MzDef) in Escherichia coli and subsequent purification by glutathione affinity chromatography yielded 2 mg/L of recombinant defensin peptide. The glutathione-S-transferase (GST)-tagged MzDef of approximately 30 kDa in size (26 KDa GST +  ~ 4 KDa MzDef peptide) was immunodetected with anti-GST antibodies. The GST-tag was successfully cleaved from the MzDef peptide by thrombin, and the removal was validated by the Tris-Tricine gel electrophoresis. The MzDef induced strong growth inhibition of Rhizoctonia solani, Fusarium verticillioides, and Aspergillus niger by 94.23%, 93.34%, and 86.25%, respectively, whereas relatively weak growth inhibitory activity of 35.42% against Fusarium solani was recorded. Moreover, strong antibacterial activities were demonstrated against E. coli and Bacillus cereus and the moderate activities against Salmonella enterica and Staphylococcus aureus at all tested concentrations (0.1, 0.2, 0.4, 0.8, 1.6, and 3.2 µM). Furthermore, the in vitro MTT assay exhibited promising anticancer activity against all tested cell lines (hepatocellular carcinoma, mammary gland breast cancer, and colorectal carcinoma colon cancer) with IC50 values ranging from 14.85 to 29.85 µg/mL. These results suggest that the recombinant peptide MzDef may serve as a potential alternative antimicrobial and anticancer agent to be used in medicinal application.

Defensins of Grasses: A Systematic Review

The grass family (Poaceae) is one of the largest families of flowering plants, growing in all climatic zones of all continents, which includes species of exceptional economic importance. The high adaptability of grasses to adverse environmental factors implies the existence of efficient resistance mechanisms that involve the production of antimicrobial peptides (AMPs). Of plant AMPs, defensins represent one of the largest and best-studied families. Although wheat and barley seed γ-thionins were the first defensins isolated from plants, the functional characterization of grass defensins is still in its infancy. In this review, we summarize the current knowledge of the characterized defensins from cultivated and selected wild-growing grasses. For each species, isolation of defensins or production by heterologous expression, peptide structure, biological activity, and structure-function relationship are described, along with the gene expression data. We also provide our results on in silico mining of defensin-like sequences in the genomes of all described grass species and discuss their potential functions. The data presented will form the basis for elucidation of the mode of action of grass defensins and high adaptability of grasses to environmental stress and will provide novel potent molecules for practical use in medicine and agriculture.

Overexpression of PtDefensin enhances resistance to Septotis populiperda in transgenic poplar

Plant defensins have been implicated in the plant defense system, but their role in poplar immunity is still unclear. In the present study, we present evidence that PtDefensin, a putative plant defensin, participates in the defense of poplar plants against Septotis populiperda infection. After the construction of recombinant plasmid PET-32a-PtDefensin, PtDefensin protein was expressed in Escherichia coli strain BL21 (DE3) and purified through Ni-IDA resin affinity chromatography. The Trx-PtDefensin fusion protein displayed no cytotoxic activity against RAW264.7 cells but had cytotoxic activity against E. coli K12D31 cells. Analyses of PtDefensin transcript abundance showed that the expression levels of PtDefensin responded to abiotic and biotic stresses. Overexpression of PtDefensin in 'Nanlin 895' poplars (Populus × euramericana cv 'Nanlin895') increased resistance to Septotis populiperda, coupled with upregulation of MYC2 (basic helix-loop-helix (bHLH) transcription factor) related to jasmonic acid (JA) signal transduction pathways and downregulation of Jasmonate-zim domain (JAZ), an inhibitor in the JA signal transduction pathway. We speculate that systemic acquired resistance (SAR) was activated in non-transgenic poplars after S. populiperda incubation, and that induced systemic resistance (ISR) was activated more obviously in transgenic poplars after S. populiperda incubation. Hence, overexpression of PtDefensin may improve the resistance of poplar plants to pathogens.

Cyclotides: From Structure to Function

This Review explores the class of plant-derived macrocyclic peptides called cyclotides. We include an account of their discovery, characterization, and distribution in the plant kingdom as well as a detailed analysis of their sequences and structures, biosynthesis and chemical synthesis, biological functions, and applications. These macrocyclic peptides are around 30 amino acids in size and are characterized by their head-to-tail cyclic backbone and cystine knot motif, which render them to be exceptionally stable, with resistance to thermal or enzymatic degradation. Routes to their chemical synthesis have been developed over the past two decades, and this capability has facilitated a wide range of mutagenesis and structure-activity relationship studies. In turn, these studies have both led to an increased understanding of their mechanisms of action as well as facilitated a range of applications in agriculture and medicine, as ecofriendly crop protection agents, and as drug leads or scaffolds for pharmaceutical design. Our overall objective in this Review is to provide readers with a comprehensive overview of cyclotides that we hope will stimulate further work on this fascinating family of peptides.

Plant evolution and environmental adaptation unveiled by long-read whole-genome sequencing of Spirodela

Aquatic plants have to adapt to the environments distinct from where land plants grow. A critical aspect of adaptation is the dynamics of sequence repeats, not resolved in older sequencing platforms due to incomplete and fragmented genome assemblies from short reads. Therefore, we used PacBio long-read sequencing of the Spirodela polyrhiza genome, reaching a 44-fold increase of contiguity with an N50 (a median of contig lengths) of 831 kb and filling 95.4% of gaps left from the previous version. Reconstruction of repeat regions indicates that sequentially nested long terminal repeat (LTR) retrotranspositions occur early in monocot evolution, featured with both prokaryote-like gene-rich regions and eukaryotic repeat islands. Protein-coding genes are reduced to 18,708 gene models supported by 492,435 high-quality full-length PacBio complementary DNA (cDNA) sequences. Different from land plants, the primitive architecture of Spirodela's adventitious roots and lack of lateral roots and root hairs are consistent with dispensable functions of nutrient absorption. Disease-resistant genes encoding antimicrobial peptides and dirigent proteins are expanded by tandem duplications. Remarkably, disease-resistant genes are not only amplified, but also highly expressed, consistent with low levels of 24-nucleotide (nt) small interfering RNA (siRNA) that silence the immune system of land plants, thereby protecting Spirodela against a wide spectrum of pathogens and pests. The long-read sequence information not only sheds light on plant evolution and adaptation to the environment, but also facilitates applications in bioenergy and phytoremediation.