Antimicrobial activity and mechanism of action of a thionin-like peptide from Capsicum annuum fruits and combinatorial treatment with fluconazole against Fusarium solani

Genome-Wide Identification and Expression Analysis of Thionin Family in Rice (Oryza sativa) and Functional Characterization of OsTHION15 in Drought Stress and ABA Stress

The OsTHION family represents a class of cysteine-rich signal peptides widely recognized for their significant roles in plant disease resistance and immunity. While members of this family are known to be induced under various biotic and abiotic stresses, their responses to environmental stressors beyond disease resistance remain underexplored. This study investigates the evolution, expression patterns, and functional roles of the OsTHION gene family in rice (Oryza sativa) under diverse stress conditions. Using sequence data from the Phytozome database, we identified 44 OsTHION family members and classified them into four groups based on phylogenetic analysis. Cis-acting element analysis revealed that the promoter regions of OsTHION genes are enriched with regulatory elements associated with light response, hormone signaling, plant growth, and stress responses. The OsTHION genes exhibit complex organ-specific expression patterns, with OsTHION30 and OsTHION36 showing ubiquitous expression, while other members are highly expressed in specific tissues or developmental stages. Under drought, salt, and low-temperature stress, OsTHION genes undergo significant expression changes, underscoring their critical role in plant adaptation to environmental challenges. Notably, OsTHION15 was markedly upregulated under drought stress, and the Osthion15 mutant displayed heightened sensitivity to drought and ABA stress, confirming its pivotal role in stress resistance. RNA sequencing analysis identified many differentially expressed genes (DEGs), primarily enriched in pathways related to ribosomal function and plant hormone signaling, suggesting that OsTHION15 may regulate stress responses through multiple mechanisms. In summary, this study advances our understanding of the OsTHION gene family and highlights its intricate involvement in regulating rice growth, development, and environmental stress responses. These findings offer valuable insights and technical support for crop improvement, with potential applications in enhancing environmental adaptability and yield stability in crops.

Plant Antimicrobial Peptides and Their Main Families and Roles: A Review of the Literature

Antimicrobial peptides (AMPs) are constituent molecules of the innate defense system and are naturally produced by all organisms. AMPs are characterized by a relatively low molecular weight (less than 10 kDa) and a variable number of cysteine residues that form disulfide bonds and contribute to the stabilization of the tertiary structure. In addition, there is a wide repertoire of antimicrobial agents against bacteria, viruses, fungi, and protozoa that can provide a large number of prototype peptides for study and biochemical manipulation. In this sense, plant AMPs stand out because they have a wide range of biological functions against microorganisms and potential applications in medicine and agriculture. Herein, we describe a mini-review of the principal AMP families, such as defensins, lipid transfer proteins (LTPs), thionins, heveins, and cyclotides. The objective of this work was to present the main discoveries regarding the biological activities of these plant AMP families, especially in the last 20 years. We also discuss the current knowledge of their biological activities, gene expression, and possible uses as antimicrobial molecules and in plant biotechnology.

Brassicaceae Mustards: Phytochemical Constituents, Pharmacological Effects, and Mechanisms of Action against Human Disease

The Brassicaceae genus consists of many economically important mustards of value for food and medicinal purposes, namely Asian mustard (Brassica juncea), ball mustard (Neslia paniculata), black mustard (B. nigra), garlic mustard (Alliaria petiolata), hedge mustard (Sisymbrium officinale), Asian hedge mustard (S. orientale), oilseed rape (B. napus), rapeseed (B. rapa), treacle mustard (Erysimum repandum), smooth mustard (S. erysimoides), white ball mustard (Calepina irregularis), white mustard (Sinapis alba), and Canola. Some of these are commercially cultivated as oilseeds to meet the global demand for a healthy plant-derived oil, high in polyunsaturated fats, i.e., B. napus and B. juncea. Other species are foraged from the wild where they grow on roadsides and as a weed of arable land, i.e., E. repandum and S. erysimoides, and harvested for medicinal uses. These plants contain a diverse range of bioactive natural products including sulfur-containing glucosinolates and other potentially valuable compounds, namely omega-3-fatty acids, terpenoids, phenylpropanoids, flavonoids, tannins, S-methyl cysteine sulfoxide, and trace-elements. Various parts of these plants and many of the molecules that are produced throughout the plant have been used in traditional medicines and more recently in the mainstream pharmaceutical and food industries. This study relates the uses of mustards in traditional medicines with their bioactive molecules and possible mechanisms of action and provides an overview of the current knowledge of Brassicaceae oilseeds and mustards, their phytochemicals, and their biological activities.

Synergistic action of synthetic peptides and amphotericin B causes disruption of the plasma membrane and cell wall in Candida albicans

The objective of this work was to evaluate the combination of synthetic peptides based on the γ-core motif of defensin PvD1 with amphotericin B (AmB) at different concentrations against Candida albicans. We applied the checkerboard assay using different concentrations of the commercial drug AmB and the synthetic peptides γ31-45PvD1++ and γ33-41PvD1++ against C. albicans, aiming to find combinations with synergistic interactions. Between these two interactions involving γ31-45PvD1++ and AmB, an additive effect was observed. One such interaction occurred at concentrations of 0.009 µM of peptide γ31-45PvD1++ and 13.23 µM of AmB and another condition of 0.019 µM of peptide γ31-45PvD1++ and 6.61 µM of AmB. The other two concentrations of the interaction showed a synergistic effect in the combination of synthetic peptide γ31-45PvD1++ and AmB, where the concentrations were 1.40 µM peptide γ31-45PvD1++ and 0.004 µM AmB and 0.70 µM γ31-45PvD1++ peptide and 0.002 µM AmB. We proceeded with analysis of the mechanism of action involving synergistic effects. This examination unveiled a range of impactful outcomes, including the impairment of mitochondrial functionality, compromise of cell wall integrity, DNA degradation, and a consequential decline in cell viability. We also observed that both synergistic combinations were capable of causing damage to the plasma membrane and cell wall, causing leakage of intracellular components. This discovery demonstrates for the first time that the synergistic combinations found between the synthetic peptide γ31-45PvD1++ and AmB have an antifungal effect against C. albicans, acting on the integrity of the plasma membrane and cell wall.

Plant Protease Inhibitors as Emerging Antimicrobial Peptide Agents: A Comprehensive Review

Antimicrobial peptides (AMPs) are important mediator molecules of the innate defense mechanisms in a wide range of living organisms, including bacteria, mammals, and plants. Among them, peptide protease inhibitors (PPIs) from plants play a central role in their defense mechanisms by directly attacking pathogens or by modulating the plant's defense response. The growing prevalence of microbial resistance to currently available antibiotics has intensified the interest concerning these molecules as novel antimicrobial agents. In this scenario, PPIs isolated from a variety of plants have shown potential in inhibiting the growth of pathogenic bacteria, protozoans, and fungal strains, either by interfering with essential biochemical or physiological processes or by altering the permeability of biological membranes of invading organisms. Moreover, these molecules are active inhibitors of a range of proteases, including aspartic, serine, and cysteine types, with some showing particular efficacy as trypsin and chymotrypsin inhibitors. In this review, we provide a comprehensive analysis of the potential of plant-derived PPIs as novel antimicrobial molecules, highlighting their broad-spectrum antimicrobial efficacy, specificity, and minimal toxicity. These natural compounds exhibit diverse mechanisms of action and often multifunctionality, positioning them as promising molecular scaffolds for developing new therapeutic antibacterial agents.

Peptide Dendrimer-Based Antibacterial Agents: Synthesis and Applications

Pathogenic bacteria cause the deaths of millions of people every year. With the development of antibiotics, hundreds and thousands of people's lives have been saved. Nevertheless, bacteria can develop resistance to antibiotics, rendering them insensitive to antibiotics over time. Peptides containing specific amino acids can be used as antibacterial agents; however, they can be easily degraded by proteases in vivo. To address these issues, branched peptide dendrimers are now being considered as good antibacterial agents due to their high efficacy, resistance to protease degradation, and low cytotoxicity. The ease with which peptide dendrimers can be synthesized and modified makes them accessible for use in various biological and nonbiological fields. That is, peptide dendrimers hold a promising future as antibacterial agents with prolonged efficacy without bacterial resistance development. Their in vivo stability and multivalence allow them to effectively target multi-drug-resistant strains and prevent biofilm formation. Thus, it is interesting to have an overview of the development and applications of peptide dendrimers in antibacterial research, including the possibility of employing machine learning approaches for the design of AMPs and dendrimers. This review summarizes the synthesis and applications of peptide dendrimers as antibacterial agents. The challenges and perspectives of using peptide dendrimers as the antibacterial agents are also discussed.

Antimicrobial Peptide Synergies for Fighting Infectious Diseases

Antimicrobial peptides (AMPs) are essential elements of thehost defense system. Characterized by heterogenous structures and broad-spectrumaction, they are promising candidates for combating multidrug resistance. Thecombined use of AMPs with other antimicrobial agents provides a new arsenal ofdrugs with synergistic action, thereby overcoming the drawback of monotherapiesduring infections. AMPs kill microbes via pore formation, thus inhibitingintracellular functions. This mechanism of action by AMPs is an advantage overantibiotics as it hinders the development of drug resistance. The synergisticeffect of AMPs will allow the repurposing of conventional antimicrobials andenhance their clinical outcomes, reduce toxicity, and, most significantly,prevent the development of resistance. In this review, various synergies ofAMPs with antimicrobials and miscellaneous agents are discussed. The effect ofstructural diversity and chemical modification on AMP properties is firstaddressed and then different combinations that can lead to synergistic action,whether this combination is between AMPs and antimicrobials, or AMPs andmiscellaneous compounds, are attended. This review can serve as guidance whenredesigning and repurposing the use of AMPs in combination with other antimicrobialagents for enhanced clinical outcomes.

Exploring the Biologically Active Metabolites Produced by Bacillus cereus for Plant Growth Promotion, Heat Stress Tolerance, and Resistance to Bacterial Soft Rot in Arabidopsis

Eight gene clusters responsible for synthesizing bioactive metabolites associated with plant growth promotion were identified in the Bacillus cereus strain D1 (BcD1) genome using the de novo whole-genome assembly method. The two largest gene clusters were responsible for synthesizing volatile organic compounds (VOCs) and encoding extracellular serine proteases. The treatment with BcD1 resulted in an increase in leaf chlorophyll content, plant size, and fresh weight in Arabidopsis seedlings. The BcD1-treated seedlings also accumulated higher levels of lignin and secondary metabolites including glucosinolates, triterpenoids, flavonoids, and phenolic compounds. Antioxidant enzyme activity and DPPH radical scavenging activity were also found to be higher in the treated seedlings as compared with the control. Seedlings pretreated with BcD1 exhibited increased tolerance to heat stress and reduced disease incidence of bacterial soft rot. RNA-seq analysis showed that BcD1 treatment activated Arabidopsis genes for diverse metabolite synthesis, including lignin and glucosinolates, and pathogenesis-related proteins such as serine protease inhibitors and defensin/PDF family proteins. The genes responsible for synthesizing indole acetic acid (IAA), abscisic acid (ABA), and jasmonic acid (JA) were expressed at higher levels, along with WRKY transcription factors involved in stress regulation and MYB54 for secondary cell wall synthesis. This study found that BcD1, a rhizobacterium producing VOCs and serine proteases, is capable of triggering the synthesis of diverse secondary metabolites and antioxidant enzymes in plants as a defense strategy against heat stress and pathogen attack.

An Overview of the Potentialities of Antimicrobial Peptides Derived from Natural Sources

Antimicrobial peptides (AMPs) are constituents of the innate immune system in every kind of living organism. They can act by disrupting the microbial membrane or without affecting membrane stability. Interest in these small peptides stems from the fear of antibiotics and the emergence of microorganisms resistant to antibiotics. Through membrane or metabolic disruption, they defend an organism against invading bacteria, viruses, protozoa, and fungi. High efficacy and specificity, low drug interaction and toxicity, thermostability, solubility in water, and biological diversity suggest their applications in food, medicine, agriculture, animal husbandry, and aquaculture. Nanocarriers can be used to protect, deliver, and improve their bioavailability effectiveness. High cost of production could limit their use. This review summarizes the natural sources, structures, modes of action, and applications of microbial peptides in the food and pharmaceutical industries. Any restrictions on AMPs' large-scale production are also taken into consideration.

Rhamnolipids and fengycins, very promising amphiphilic antifungal compounds from bacteria secretomes, act on Sclerotiniaceae fungi through different mechanisms

Rhamnolipids (RLs) and fengycins (FGs) are amphiphilic lipid compounds from bacteria secretomes proposed to replace synthetic pesticides for crop protection. They both display plant defense triggering properties and direct antimicrobial activities. In particular, they have well reported antifungal effects against phytopathogenic fungi. RLs and FGs are considered to act through a direct interaction with membrane lipids and a destabilization of microorganism plasma membrane, thereby limiting the risk of resistance emergence. The main objective of this work was to gain insights in the antimycelial mode of action of these metabolites to promote them as environment and human health friendly biocontrol solutions. Their biocidal effects were studied on two Sclerotiniaceae fungi responsible for diseases in numerous plant species worldwide. We show here that different strains of Botrytis cinerea and Sclerotinia sclerotiorum have opposite sensitivities to RLs and FGs on plate experiments. Overall, B. cinerea is more sensitive to FGs while S. sclerotiorum is more sensitive to RLs. Electron microscopy observations demonstrated that RLs induce mycelial destructuring by asperities emergence and hyphal fusions whereas FGs promote swelling and formation of vesicle-like structures due to vacuole fusions and autophagy. Permeability studies, phosphatidylserine externalization and reactive oxygen species production assessments showed a programmed cell death triggering by RLs at medium concentrations (until 50 μg mL⁻¹) and necrosis characteristics at higher concentration. Programmed cell death was always observed on hyphae treated with FGs. Quantifications of mycelial ergosterol content indicated that a higher ergosterol rate in S. sclerotiorum correlates with increasing sensitivity to RLs. Oppositely, a lower ergosterol rate in B. cinerea correlates with increasing sensitivity to FGs, which was confirmed by ergosterol biosynthesis inhibition with tebuconazole. This gain of knowledge will help to better understand the mode of action of RLs and FGs to fight specific plant fungal diseases.

C apsicum fruits as functional ingredients with antimicrobial activity: an emphasis on mechanisms of action

Capsicum spp. fruits (CFs) are a basic ingredient in the diet and have been used as active ingredients in the pharmaceutical, cosmetic, and food products, due to their antioxidant, anti-inflammatory, antiseptic, and antimicrobial properties. The antimicrobial activity is the most studied property due to its effectiveness against pathogenic species, however, few studies have focused on the mechanisms of action involved. Therefore, this review discusses the effects generated by the CFs compounds on the viability and metabolism of microorganisms, highlighting the mechanisms by which these compounds exert their antimicrobial effects. The information provided shows that CFs are mainly source of capsaicinoids and phenolic compounds responsible for the inhibition of bacteria, yeasts, and fungi, through an increase in the permeabilization of the membrane and cell wall. Also, these compounds show an antiviral effect associated with the inactivation of virus binding proteins, preventing their replication and infection. Despite this, there is still a lack of information about the mechanisms that regulate the interactions between CFs compounds and food-important-microorganisms. Therefore, future research should focus on new antimicrobial compounds from CFs for their subsequent use against novel infectious agents, mainly virus of importance in health such as SARS-CoV-2.

Plant-Derived Antimicrobial Peptides: Novel Preservatives for the Food Industry

Food spoilage is a widespread issue brought on by the undesired growth of microbes in food products. Thousands of tons of usable food or food products are wasted every day due to rotting in different parts of the world. Several food preservation techniques are employed to prevent food from rotting, including the use of natural or manufactured chemicals or substances; however, the issue persists. One strategy for halting food deterioration is the use of plant-derived antimicrobial peptides (AMPs), which have been investigated for possible bioactivities against a range of human, plant, and food pathogens. The food industry may be able to benefit from the development of synthetic AMPs, produced from plants that have higher bioactivity, better stability, and decreased cytotoxicity as a means of food preservation. In order to exploit plant-derived AMPs in various food preservation techniques, in this review, we also outline the difficulties in developing AMPs for use as commercial food preservatives. Nevertheless, as technology advances, it will soon be possible to fully explore the promise of plant-derived AMPs as food preservatives.

Plant antimicrobial peptides: An overview about classification, toxicity and clinical applications

Antimicrobial peptides, also known as AMPs, are cationic and amphipathic molecules found in all living organisms, composing part of the defense mechanisms against various pathogens, including fungi, viruses, bacteria, and nematodes. AMPs derived from plants are the focus of this review because they have gained attention as alternative molecules to overcome pathogen resistance as well as new drugs to combat cancer. Plant AMPs are generally classified based on their sequences and structures, as thionins, defensins, hevein-like peptides, knottins, stable-like peptides, lipid transfer proteins, snakins, and cyclotides. Although there are studies reporting the toxicity of plant AMPs to nontarget cells or limitations of oral administration, synthetic AMPs with reduced toxicity or allergenicity, or greater resistance to peptidases can be designed by using different bioinformatics tools. Thus, this review provides information about the classification of plant AMPs, their characteristics, mechanisms of action, hemolytic and cytotoxic potential, possible applications in the medical field, and finally, the use of bioinformatics to help design synthetic AMPs with improved features.

Intracellular mechanism of antimicrobial peptide HJH-3 against Salmonella pullorum

To explore the potential intracellular mechanism of the antimicrobial peptide HJH-3 in killing Salmonella, a DNA blocking test and scanning electron microscopy (SEM) were used to determine the ability of the peptide to bind bacterial DNA in vitro. Laser confocal analysis and electron microscopy were used to observe the binding of antimicrobial peptide HJH-3 and Salmonella DNA, and flow cytometry was used to analyze the effect of antimicrobial peptides on cell division in vivo. The results showed that HJH-3 can bind to DNA to block the diffusion and migration of DNA in agarose gel. Laser confocal microscopy revealed that antimicrobial peptide HJH-3 penetrated the bacterial cell membrane and bound with bacterial DNA. Transmission electron microscopy showed that antimicrobial peptide HJH-3 aggregated in the nucleoid of Salmonella cells, and through a channel in the membrane destroyed by the antimicrobial peptide, DNA and other intracellular contents were excreted, and polymerized DNA was fragmented. The results of the flow cytometry analysis confirmed that the death rate of Salmonella increased significantly after exposure to antimicrobial peptide HJH-3 and increased with increasing antimicrobial peptide concentration. These results suggest that AMP HJH-3 may be a candidate antimicrobial agent to treat infectious diseases caused by Salmonella pullorum.

To explore the potential intracellular mechanism of the antimicrobial peptide HJH-3 in killing Salmonella, a DNA blocking test and scanning electron microscopy (SEM) were used to determine the ability of the peptide to bind bacterial DNA in vitro.

Broad-spectrum antifungal activity of lipopeptide brevilaterin B and its inhibition effects against Fusarium oxysporum and Penicillium chrysogenum

AIMS

Brevilaterin B is a natural antimicrobial lipopeptide produced by Brevibacillus laterosporus S62-9. However, its antifungal spectrum and modes of action are still unclear. Herein, we investigated the detailed antifungal activity of brevilaterin B against 33 pathogenic fungi and the antifungal effects against two sensitive fungi in vitro and in vivo.

METHODS AND RESULTS

Brevilaterin B exhibited inhibitory activity against 33 pathogenic fungi involved in plant disease and food spoilage at the minimum inhibitory concentrations (MICs) range of 16-128 μg ml^-1 . The antifungal effects were further studied by Fusarium oxysporum and Penicillium chrysogenum. Both spore germination and mycelium growth were inhibited by brevilaterin B at sub-MIC. Transmission electron microscopy and fluorescent dye staining assays indicated brevilaterin B damaged cell integrity and induced apoptosis. In vivo tests, brevilaterin B inhibited the infection of F. oxysporum to Dendrobium officinale and P. chrysogenum to mandarin (Citrus reticulata) at 500 μg ml^-1 , respectively.

CONCLUSIONS

Brevilaterin B showed broad-spectrum antifungal activity against 33 pathogenic fungi. And its antifungal modes of action were proposed as damaging cell integrity and inducing cell apoptosis. The lipopeptide is promising to control F. oxysporum in the D. officinale and P. chrysogenum in the mandarin.

SIGNIFICANCE AND IMPACT OF STUDY

The research provided insights into antifungal modes of action of brevilaterin B. The lipopeptide brevilaterin B is potential to be developed as a broad-spectrum antifungal agent for agricultural biocontrol and postharvest storage.

Amino acid-derived defense metabolites from plants: A potential source to facilitate novel antimicrobial development

For millennia, humanity has relied on plants for its medicines, and modern pharmacology continues to reexamine and mine plant metabolites for novel compounds and to guide improvements in biological activity, bioavailability, and chemical stability. The critical problem of antibiotic resistance and increasing exposure to viral and parasitic diseases has spurred renewed interest into drug treatments for infectious diseases. In this context, an urgent revival of natural product discovery is globally underway with special attention directed toward the numerous and chemically diverse plant defensive compounds such as phytoalexins and phytoanticipins that combat herbivores, microbial pathogens, or competing plants. Moreover, advancements in “omics,” chemistry, and heterologous expression systems have facilitated the purification and characterization of plant metabolites and the identification of possible therapeutic targets. In this review, we describe several important amino acid–derived classes of plant defensive compounds, including antimicrobial peptides (e.g., defensins, thionins, and knottins), alkaloids, nonproteogenic amino acids, and phenylpropanoids as potential drug leads, examining their mechanisms of action, therapeutic targets, and structure–function relationships. Given their potent antibacterial, antifungal, antiparasitic, and antiviral properties, which can be superior to existing drugs, phytoalexins and phytoanticipins are an excellent resource to facilitate the rational design and development of antimicrobial drugs.

Antimicrobial Peptides: a New Frontier in Antifungal Therapy

Invasive fungal infections in humans are generally associated with high mortality, making the choice of antifungal drug crucial for the outcome of the patient. The limited spectrum of antifungals available and the development of drug resistance represent the main concerns for the current antifungal treatments, requiring alternative strategies. Antimicrobial peptides (AMPs), expressed in several organisms and used as first-line defenses against microbial infections, have emerged as potential candidates for developing new antifungal therapies, characterized by negligible host toxicity and low resistance rates. Most of the current literature focuses on peptides with antibacterial activity, but there are fewer studies of their antifungal properties. This review focuses on AMPs with antifungal effects, including their in vitro and in vivo activities, with the biological repercussions on the fungal cells, when known. The classification of the peptides is based on their mode of action: although the majority of AMPs exert their activity through the interaction with membranes, other mechanisms have been identified, including cell wall inhibition and nucleic acid binding. In addition, antifungal compounds with unknown modes of action are also described. The elucidation of such mechanisms can be useful to identify novel drug targets and, possibly, to serve as the templates for the synthesis of new antimicrobial compounds with increased activity and reduced host toxicity.

Characterization and antifungal activity of a plant peptide expressed in the interaction between Capsicum annuum fruits and the anthracnose fungus

Plant defensins are low molecular weight basic peptides ranging from 5 to 7 kDa, with capacity of inhibiting various pathogens, including fungi. They are present in different tissues of plants, including floral parts and fruits of Capsicum sp. The IIF48 extract, present in immature fruits of Capsicum annuum inoculated with C. gloeosporioides, was able to inhibit up to 100% growth ‘in vitro’ of the fungus Colletotrichum gloeosporioides. The main objective of this work was the purification and antifungal activity characterization of a defense-related plant defensin-like isolated of the IIF48 immature fruits extract. The IIF48 extract was subjected to HPLC purification and 13 fractions were obtained, followed by a tricine gel electrophoresis to obtain the protein profile. The different fractions were submitted to a growth inhibition assay against C. gloeosporioides fungus. Fraction 7 (F7) was the most active causing 73% inhibition. Because of the higher F7 activity and the presence of only a peptide of approximately 5 kDa this fraction was subjected to N-terminal sequencing. F7 fraction was carried out plasma membrane permeabilization assays, induction of intracellular ROS production analysis and investigated mitochondrial membrane potential. The F7 fraction showed significant inhibitory activity on the tested fungus, besides promoting membrane permeabilization, induction of endogenous ROS production in Colletotrichum cells and impairing mitochondrial functionality. The first 18 amino acid sequence of the F7 fraction peptide suggests homology to plant-like defensin and was named IIFF7Ca. We also concluded that IIFF7Ca peptide has an effective antimicrobial action against the fungus C. gloeosporioides.

Antimicrobial peptides from Capsicum chinense fruits: agronomic alternatives against phytopathogenic fungi

In recent years, the antimicrobial activity of peptides isolated from a wide variety of organs from plant species has been reported. However, a few studies have investigated the potential of antimicrobial peptides (AMPs) found in fruits, especially Capsicum chinense (pepper). The present study aimed to purify and characterize peptides from Capsicum chinense fruits and evaluate their inhibitory activities against different phytopathogenic fungi and also analyze the possible mechanisms of action involved in microbial inhibition. After fruit protein extraction and high-performance liquid chromatography (HPLC), different fractions were obtained, named F1 to F10. Peptides in the F4 and F5 fractions were sequenced and revealed similarity with the plant antimicrobial peptides like non-specific lipid transfer proteins and defensin-like peptide. The F4 and F5 fractions presented strong antimicrobial activity against the fungus Fusarium solani and Fusarium oxysporum, causing toxic effects on these fungi, leading to membrane permeabilization, endogenous reactive oxygen species increase, activation of metacaspase and loss of mitochondrial function.

Antifungal Effect of A Chimeric Peptide Hn-Mc against Pathogenic Fungal Strains

It is difficult to identify new antifungal agents because of their eukaryotic nature. However, antimicrobial peptides can well differentiate among cell types owing to their variable amino acid content. This study aimed to investigate the antifungal effect of Hn-Mc, a chimeric peptide comprised of the N-terminus of HPA3NT3 and the C-terminus of melittin. We evaluated its potent antifungal activity at low minimal inhibitory concentrations (MICs) ranging from 1–16 μM against pathogenic yeast and molds. The cell-type specificity of Hn-Mc was mediated through the formation of a random α-helical structure to mimic the fungal membrane environment. Furthermore, Hn-Mc caused cell death in C. tropicalis and F. oxysporum by inducing apoptosis via the generation of reactive oxygen species (ROS) due to mitochondrial damage. The present results indicate that Hn-Mc has a high affinity for the fungal plasma membrane and induces apoptosis in fungal cells, and provide guidance for the development of new antifungal agents.

Antifungal Peptides as Therapeutic Agents

Fungi have been used since ancient times in food and beverage-making processes and, more recently, have been harnessed for the production of antibiotics and in processes of relevance to the bioeconomy. Moreover, they are starting to gain attention as a key component of the human microbiome. However, fungi are also responsible for human infections. The incidence of community-acquired and nosocomial fungal infections has increased considerably in recent decades. Antibiotic resistance development, the increasing number of immunodeficiency- and/or immunosuppression-related diseases and limited therapeutic options available are triggering the search for novel alternatives. These new antifungals should be less toxic for the host, with targeted or broader antimicrobial spectra (for diseases of known and unknown etiology, respectively) and modes of actions that limit the potential for the emergence of resistance among pathogenic fungi. Given these criteria, antimicrobial peptides with antifungal properties, i.e., antifungal peptides (AFPs), have emerged as powerful candidates due to their efficacy and high selectivity. In this review, we provide an overview of the bioactivity and classification of AFPs (natural and synthetic) as well as their mode of action and advantages over current antifungal drugs. Additionally, natural, heterologous and synthetic production of AFPs with a view to greater levels of exploitation is discussed. Finally, we evaluate the current and potential applications of these peptides, along with the future challenges relating to antifungal treatments.

Arabidopsis thionin-like genes are involved in resistance against the beet-cyst nematode (Heterodera schachtii)

Plants express various antimicrobial peptides including thionins to protect themselves against pathogens. It was recently found that, in addition to four thionin genes, Arabidopsis contains 67 thionin-like (ThiL) genes including six pseudogenes. It is known that thionins have antimicrobial activity and are part of the plant defense system, however, nothing is known about ThiL genes. In this study, we present a bioinformatic analysis of the (ThiL) gene family in Arabidopsis. We identified 15 different motifs which positioned the ThiL peptides in four groups. A comparison of amino acid sequences showed that the ThiL peptides are actually more similar to the acidic domain of thionin proproteins than to the thionin domain. We selected 10 ThiL genes to study the expression and possible function in the Arabidopsis plant. RT-PCR and promoter:GUS fusions showed that most genes were expressed at a very low level but in several organs and at different developmental stages. Some genes were also expressed in syncytia induced by the beet cyst nematode Heterodera schachti in roots while others were downregulated in syncytia. Some overexpression lines supported lower number of nematodes that developed on the roots after inoculation. Two of the genes resulted in a strong hypersensitive response when infiltrated into leaves of Nicotiana benthamiana. These results indicate that ThiL genes might be involved in the response to biotic stress. ThiL genes have been expanded in the Brassicales and specifically the Brassicaceae. The most extreme example is the CRP2460 subfamily that contains 28 very closely related genes from Arabidopsis which are mostly the result of tandem duplications.

Buckwheat Antifungal Protein with Biocontrol Potential To Inhibit Fungal ( Botrytis cinerea) Infection of Cherry Tomato

A 11 kDa antifungal protein FEAP was purified from buckwheat ( Fagopyrum esculentum) seed extract with a procedure involving (NH₄)₂SO₄ precipitation and chromatography on SP-Sepharose, Affi-gel blue gel, Mono S, and Superdex peptide. Its N-terminal sequence was AQXGAQGGGAT, resembling those of buckwheat peptides Fα-AMP1 and Fα-AMP2. FEAP exhibited thermostability (20-100 °C) and acid resistance (pH 1-5). Its antifungal activity was retained in the presence of 10-150 mmol/L of K⁺, Mn²⁺, or Fe³⁺ ions, 10-50 mmol/L of Ca²⁺ or Mg²⁺ ions, and 50% methanol, 50% ethanol, 50% isopropanol, or 50% chloroform. Its half-maximal inhibitory concentrations toward spore germination and mycelial growth in Botrytis cinerea were 79.9 and 236.7 μg/mL, respectively. Its antifungal activity was superior to the fungicide cymoxanil mancozeb (248.1 μg/mL). FEAP prevented B. cinerea from infecting excised leaves, intact leaves, and isolated fruits of cherry tomato. Its mechanism involved induction of an increase in cell membrane permeability and a decrease in mitochondrial membrane potential.

Biochemical analysis of antimicrobial peptides in two different Capsicum genotypes after fruit infection by Colletotrichum gloeosporioides

There are several phytosanitary problems that have been causing serious damage to the Capsicum crops, including anthracnose. Upon attack by certain pathogens, various protein molecules are produced, which are known as proteins related to pathogenesis (PR proteins), including antimicrobial peptides such as protease inhibitors, defensins and lipid transfer proteins (LTPs). The objective of this work is to identify antimicrobial proteins and/or peptides of two genotypes from Capsicum annuum fruits infected with Colletotrichum gloeosporioides. The fungus was inoculated into Capsicum fruits by the deposition of a spore suspension (10⁶ conidia ml⁻¹), and after 24 and 48 h intervals, the fruits were removed from the humid chamber and subjected to a protein extraction process. Protein analysis of the extracts was performed by tricine gel electrophoresis and Western blotting. The distinctive bands between genotypes in the electrophoresis profiles were subjected to mass spectrometry sequencing. Trypsin inhibition assays, reverse zymographic detection of protease inhibition and β-1,3-glucanase activity assays were also performed and extracts were also tested for their ability to inhibit the growth of C. gloeosporioides fungi ‘in vitro’. There were several low molecular weight proteins in all treated samples, and some treatments in which antimicrobial peptides such as defensin, lipid transfer protein (LTP) and protease inhibitor have been identified. It was shown that the green fruits are more responsive to infection, showing the production of antimicrobial peptides in response to injury and inoculation of the fungus, what did not occur in ripe fruits under any treatment.

Improved smallest peptides based on positive charge increase of the γ-core motif from PνD1 and their mechanism of action against Candida species

BACKGROUND

Plant defensins have a hallmark γ-core motif (GXCX3-9C) that is related to their antimicrobial properties. The aim of this work was to design synthetic peptides based on the region corresponding to the PvD1 defensin γ-core that are the smallest amino acid sequences that bear the strongest biological activity.

METHODS

We made rational substitutions of negatively charged amino acid residues with positively charged ones, and the reduction in length in the selected PvD1 γ-core sequence to verify whether the increased net positive charges and shortened length are related to the increase in antifungal activity. Herein, we opted to evaluate the action mechanism of γ33-41 PvD1 ++ peptide due to its significant inhibitory effect on tested yeasts. In addition, it is the smallest construct comprising only nine amino acid residues, giving it a better possibility to be a prototype for designing a new antifungal drug, with lower costs to the pharmaceutical industry while still maintaining the strongest antimicrobial properties.

RESULTS

The γ33-41 PvD1 ++ peptide caused the most toxic effects in the yeast Candida buinensis, leading to membrane permeabilization, viability loss, endogenous reactive oxygen species increase, the activation of metacaspase, and the loss of mitochondrial functionality, suggesting that this peptide triggers cell death via apoptosis.

CONCLUSION

We observed that the antifungal activity of PvD1 is not strictly localized in the structural domain, which comprises the γ-core region and that the increase in the net positive charge is directly related to the increase in antifungal activity.

In Silico Analyses of Rice Thionin Genes and the Antimicrobial Activity of OsTHION15 Against Phytopathogens

Thionins are a family of antimicrobial peptides. We performed in silico expression analyses of the 44 rice (Oryza sativa) thionins (OsTHIONs). Modulated expression levels of OsTHIONs under different treatments suggest their involvement in many processes, including biotic, abiotic, and nutritional stress responses, and in hormone signaling. OsTHION15 (LOC_Os06g32600) was selected for further characterization based on several in silico analyses. OsTHION15 in O. sativa subsp. indica 'KDML 105' was expressed in all of the tissues and organs examined, including germinating seed, leaves, and roots of seedlings and mature plants, and inflorescences. To investigate the antimicrobial activity of OsTHION15, we produced a recombinant peptide in Escherichia coli Rosetta-gami (DE3). The recombinant OsTHION15 exhibited inhibitory activities toward rice-pathogenic bacteria such as Xanthomonas oryzae pv. oryzae and Pectobacterium carotovorum pv. atroseptica, with minimum inhibitory concentrations of 112.6 and 14.1 µg ml^-1, respectively. A significant hyphal growth inhibition was also observed toward Fusarium oxysporum f. sp. cubense and Helminthosporium oryzae. In addition, we demonstrated the in planta antibacterial activity of this peptide in Nicotiana benthamiana against X. campestris pv. glycines. These activities suggest the possible application of OsTHION15 in plant disease control.

Plant thionins: structure, biological functions and potential use in biotechnology

Antimicrobial peptides (AMPs) are important components of defense system in both plants and animals. They represent an ancient mechanism of innate immunity providing rapid first line of defense against pathogens. Plant AMPs are classified into several families: thionins, defensins, nonspecific lipid-transfer proteins, hevein- and knottin-type peptides, hairpinins and macrocyclic peptides (cyclotides). The review focuses on the thionin family. Thionins comprise a plant-specific AMP family that consists of short (~5 kDA) cysteine-rich peptides containing 6 or 8 cysteine residues with antimicrobial and toxic properties. Based on similarity in amino acid sequences and the arrangement of disulphide bonds, five structural classes of thionins are discriminated. The three-dimensional structures of a number of thionins were determined. The amphipathic thionin molecule resembles the Greek letter Г, in which the long arm is formed by two antiparallel α-helices, while the short one, by two parallel β-strands. The residues responsible for the antimicrobial activity of thionins were identified. Thionins are synthesized as precursor proteins consisting of a signal peptide, the mature peptide region and the C-terminal prodomain. Thionins protect plants from pathogenic bacteria and fungi acting directly on the membranes of microorganisms at micromolar concentrations, although their precise mode of action remains unclear. In addition to plant pathogens, thionins inhibit growth of a number of human pathogens and opportunistic microorganisms, such as Candida spp., Saccharomyces cerevisiae, Fusarium solani, Staphylococcus aureus and Escherichia coli. Thionins are toxic to different types of cells including mammalian cancer cell lines. Transgenic plants expressing thionin genes display enhanced resistance to pathogens. A wide range of biological activities makes thionins promising candidates for practical application in agriculture and medicine.

Coffea canephora Peptides in Combinatorial Treatment with Fluconazole: Antimicrobial Activity against Phytopathogenic Fungus

The objective of the present study was to evaluate the antimicrobial activity of the Cc-LTP2 and Cc-GRP peptides isolated from Coffea canephora seeds and their possible synergistic activity with the azole drug fluconazole and characterize their mechanisms of action on cells of pathogenic fungi. Cc-LTP2 and Cc-GRP alone or in combination with 20 µg/mL of fluconazole were evaluated for their antimicrobial activity on the fungus Fusarium solani, and the effects of these peptides on the permeability of membranes and the induction of oxidative stress were determined. Our results show that these peptides at a concentration of 400 µg/mL combined with 20 µg/mL of fluconazole were able to inhibit the growth of the tested fungi, promote changes in their growth pattern, permeabilize the membrane, and induce reactive oxygen species (ROS). Some of these results were also observed with the peptides alone or with fluconazole alone, suggesting that the peptides act synergistically, promoting the potentiation of antimicrobial action. In this study, it was shown that Cc-LTP2 and Cc-GRP in combination with fluconazole were able to inhibit the growth of the fungus F. solani, to promote permeabilization of its membrane, and to induce the production of ROS, suggesting a combinatorial activity between the peptides and fluconazole.

Programmed cell death in yeast by thionin-like peptide from Capsicum annuum fruits involving activation of caspases and extracellular H+ flux

CaThi is a thionin-like peptide isolated from fruits of Capsicum annuum, which has strong antimicrobial activity against bacteria, yeasts and filamentous fungi, and induced reactive oxygen species (ROS) in fungi. ROS are molecules that appear in the early stages of programmed cell death or apoptosis in fungi. Due to this fact, in this work we analyzed some events that may be related to process of apoptosis on yeast induced by CaThi. To investigate this possibility, we evaluated phosphatidylserine (PS) externalization, presence of active caspases and the ability of CaThi to bind to DNA in Candida tropicalis cells. Additionally, we investigated mitochondrial membrane potential, cell surface pH, and extracellular H⁺ fluxes in C. tropicalis cells after treatment with CaThi. Our results showed that CaThi induced PS externalization in the outer leaflet of the cell membrane, activation of caspases, and it had the ability for DNA binding and to dissipate mitochondrial membrane potential. In addition, the cell surface pH increased significantly when the C. tropicalis cells were exposed to CaThi which corroborates with ~96% inhibition on extracellular H⁺ efflux. Taking together, these data suggest that this peptide is capable of promoting an imbalance in pH homeostasis during yeast cell death playing a modulatory role in the H⁺ transport systems. In conclusion, our results strongly indicated that CaThi triggers apoptosis in C. tropicalis cells, involving a pH signaling mechanism.

Immunomodulatory effects of thionin Thi2.1 from Arabidopsis thaliana on bovine mammary epithelial cells

Antimicrobial peptides (AMPs) are key elements of plant defense mechanisms, resembling conserved protection strategies also present in mammals. Among the AMPs, plant thionins are particularly interesting due that display antibacterial and antifungal activities. In Arabidopsis thaliana have been described four thionins: Thi2.1, Thi2.2, Thi2.3 and Thi2.4. Work from our group shows that Thi2.1 expressed by bovine endothelial cells has direct antibacterial activity against Staphylococcus aureus mastitis isolates, bacteria able to persist inside bovine mammary epithelial cells (bMECs). Thus, the objective of this work was to analyze the immunomodulatory effects of the AMP thionin Thi2.1 from A. thaliana on bMECs during S. aureus infection. According to the results, S. aureus internalization into bMECs was reduced in cells pre-treated with Thi2.1 at 5 and 10 μg/mL during 24 h, effect related to the participation of TLR2. In addition, bMECs pre-treated with Thi2.1 (24 h) significantly increased TNF-α (~2-fold) and IL-6 (~7-fold), whereas decreased IL-10 gene expression (~0.5-fold). Interestingly, Thi2.1 inhibits the up-regulation induced by S. aureus of TNF-α and IL-10 gene expression, as well as NO production. In addition, Thi2.1 (10 μg/mL) up-regulates the expression of the chemokine IL-8 (~3-fold) in infected bMECs. Some of these effects are related to TLR2 activation. In this sense, Thi2.1 also reduces S. aureus-induced TLR2 gene expression and membrane abundance. In conclusion, Thi2.1 from A. thaliana modulates bMEC innate immune response by inducing the production of pro- and anti-inflammatory molecules while inhibits S. aureus internalization. Some of these effects are mediated by TLR2.