Two novel antimicrobial defensins from rice identified by gene coexpression network analyses

Plant peptides - redefining an area of ribosomally synthesized and post-translationally modified peptides

Covering 1965 to February 2024Plants are prolific peptide chemists and are known to make thousands of different peptidic molecules. These peptides vary dramatically in their size, chemistry, and bioactivity. Despite their differences, all plant peptides to date are biosynthesized as ribosomally synthesized and post-translationally modified peptides (RiPPs). Decades of research in plant RiPP biosynthesis have extended the definition and scope of RiPPs from microbial sources, establishing paradigms and discovering new families of biosynthetic enzymes. The discovery and elucidation of plant peptide pathways is challenging due to repurposing and evolution of housekeeping genes as both precursor peptides and biosynthetic enzymes and due to the low rates of gene clustering in plants. In this review, we highlight the chemistry, biosynthesis, and function of the known RiPP classes from plants and recommend a nomenclature for the recent addition of BURP-domain-derived RiPPs termed burpitides. Burpitides are an emerging family of cyclic plant RiPPs characterized by macrocyclic crosslinks between tyrosine or tryptophan side chains and other amino acid side chains or their peptide backbone that are formed by copper-dependent BURP-domain-containing proteins termed burpitide cyclases. Finally, we review the discovery of plant RiPPs through bioactivity-guided, structure-guided, and gene-guided approaches.

An endophytic fungus interacts with the defensin-like protein OsCAL1 to regulate cadmium allocation in rice

Defensin-like proteins are conserved in multicellular organisms and contribute to innate immune responses against fungal pathogens. In rice, defensins play a novel role in regulating cadmium (Cd) efflux from the cytosol. However, whether the antifungal activity of defensins correlates with Cd-efflux function remains unknown. In this study, we isolated an endophytic Fusarium, designed Fo10, by a comparative microbiome analysis of rice plants grown in a paddy contaminated with Cd. Fo10 is tolerant to high levels of Cd, but is sensitive to the defensin-like protein OsCAL1, which mediates Cd efflux to the apoplast. We found that Fo10 symbiosis in rice is regulated by OsCAL1 dynamics, and Fo10 coordinates multiple plant processes, including Cd uptake, vacuolar sequestration, efflux to the environment, and formation of Fe plaques in the rhizosphere. These processes are dependent on the salicylic acid signaling pathway to keep Cd levels low in the cytosol of rice cells and to decrease Cd levels in rice grains without any yield penalty. Fo10 also plays a role in Cd tolerance in the poaceous crop maize and wheat, but has no observed effects in the eudicot plants Arabidopsis and tomato. Taken together, these findings provide insights into the mechanistic basis underlying how a fungal endophyte and host plant interact to control Cd accumulation in host plants by adapting defense responses to promote the establishment of a symbiosis that permits adaptation to high-Cd environments.

Genetic Mapping of the Root Mycobiota in Rice and its Role in Drought Tolerance

BACKGROUND

Rice is the second most produced crop worldwide, but is highly susceptible to drought. Micro-organisms can potentially alleviate the effects of drought. The aim of the present study was to unravel the genetic factors involved in the rice-microbe interaction, and whether genetics play a role in rice drought tolerance. For this purpose, the composition of the root mycobiota was characterized in 296 rice accessions (Oryza sativa L. subsp. indica) under control and drought conditions. Genome wide association mapping (GWAS) resulted in the identification of ten significant (LOD > 4) single nucleotide polymorphisms (SNPs) associated with six root-associated fungi: Ceratosphaeria spp., Cladosporium spp., Boudiera spp., Chaetomium spp., and with a few fungi from the Rhizophydiales order. Four SNPs associated with fungi-mediated drought tolerance were also found. Genes located around those SNPs, such as a DEFENSIN-LIKE (DEFL) protein, EXOCYST TETHERING COMPLEX (EXO70), RAPID ALKALINIZATION FACTOR-LIKE (RALFL) protein, peroxidase and xylosyltransferase, have been shown to be involved in pathogen defense, abiotic stress responses and cell wall remodeling processes. Our study shows that rice genetics affects the recruitment of fungi, and that some fungi affect yield under drought. We identified candidate target genes for breeding to improve rice-fungal interactions and hence drought tolerance.

Dual-function DEFENSIN 8 mediates phloem cadmium unloading and accumulation in rice grains

Grain cadmium (Cd) is translocated from source to sink tissues exclusively via phloem, though the phloem Cd unloading transporter has not been identified yet. Here, we isolated and functionally characterized a defensin-like gene DEFENSIN 8 (DEF8) highly expressed in rice (Oryza sativa) grains and induced by Cd exposure in seedling roots. Histochemical analysis and subcellular localization detected DEF8 expression preferentially in pericycle cells and phloem of seedling roots, as well as in phloem of grain vasculatures. Further analysis demonstrated that DEF8 is secreted into extracellular spaces possibly by vesicle trafficking. DEF8 bound to Cd in vitro, and Cd efflux from protoplasts as well as loading into xylem vessels decreased in the def8 mutant seedlings compared with the wild type. At maturity, significantly less Cd accumulation was observed in the mutant grains. These results suggest that DEF8 is a dual function protein that facilitates Cd loading into xylem and unloading from phloem, thus mediating Cd translocation from roots to shoots and further allocation to grains, representing a phloem Cd unloading regulator. Moreover, essential mineral nutrient accumulation as well as important agronomic traits were not affected in the def8 mutants, suggesting DEF8 is an ideal target for breeding low grain Cd rice.

Legume NCRs and nodule-specific defensins of actinorhizal plants—Do they share a common origin?

The actinorhizal plant Datisca glomerata (Datiscaceae, Cucurbitales) establishes a root nodule symbiosis with actinobacteria from the earliest branching symbiotic Frankia clade. A subfamily of a gene family encoding nodule-specific defensin-like cysteine-rich peptides is highly expressed in D. glomerata nodules. Phylogenetic analysis of the defensin domain showed that these defensin-like peptides share a common evolutionary origin with nodule-specific defensins from actinorhizal Fagales and with nodule-specific cysteine-rich peptides (NCRs) from legumes. In this study, the family member with the highest expression levels, DgDef1, was characterized. Promoter-GUS studies on transgenic hairy roots showed expression in the early stage of differentiation of infected cells, and transient expression in the nodule apex. DgDef1 contains an N-terminal signal peptide and a C-terminal acidic domain which are likely involved in subcellular targeting and do not affect peptide activity. In vitro studies with E. coli and Sinorhizobium meliloti 1021 showed that the defensin domain of DgDef1 has a cytotoxic effect, leading to membrane disruption with 50% lethality for S. meliloti 1021 at 20.8 μM. Analysis of the S. meliloti 1021 transcriptome showed that, at sublethal concentrations, DgDef1 induced the expression of terminal quinol oxidases, which are associated with the oxidative stress response and are also expressed during symbiosis. Overall, the changes induced by DgDef1 are reminiscent of those of some legume NCRs, suggesting that nodule-specific defensin-like peptides were part of the original root nodule toolkit and were subsequently lost in most symbiotic legumes, while being maintained in the actinorhizal lineages.

Multi-Omics Approaches Unravel Specific Features of Embryo and Endosperm in Rice Seed Germination

Seed germination and subsequent seedling growth affect the final yield and quality of the crop. Seed germination is defined as a series of processes that begins with water uptake by a quiescent dry seed and ends with the elongation of embryonic axis. Rice is an important cereal crop species, and during seed germination, two tissues function in a different manner; the embryo grows into a seedling as the next generation and the endosperm is responsible for nutritional supply. Toward understanding the integrated roles of each tissue at the transcriptional, translational, and metabolic production levels during germination, an exhaustive "multi-omics" analysis was performed by combining transcriptomics, label-free shotgun proteomics, and metabolomics on rice germinating embryo and endosperm, independently. Time-course analyses of the transcriptome and metabolome in germinating seeds revealed a major turning point in the early phase of germination in both embryo and endosperm, suggesting that dramatic changes begin immediately after water imbibition in the rice germination program at least at the mRNA and metabolite levels. In endosperm, protein profiles mostly showed abundant decreases corresponding to 90% of the differentially accumulated proteins. An ontological classification revealed the shift from the maturation to the germination process where over-represented classes belonged to embryonic development and cellular amino acid biosynthetic processes. In the embryo, 19% of the detected proteins are differentially accumulated during germination. Stress response, carbohydrate, fatty acid metabolism, and transport are the main functional classes representing embryo proteome change. Moreover, proteins specific to the germinated state were detected by both transcriptomic and proteomic approaches and a major change in the network operating during rice germination was uncovered. In particular, concomitant changes of hormonal metabolism-related proteins (GID1L2 and CNX1) implicated in GAs and ABA metabolism, signaling proteins, and protein turnover events emphasized the importance of such biological networks in rice seeds. Using metabolomics, we highlighted the importance of an energetic supply in rice seeds during germination. In both embryo and endosperm, starch degradation, glycolysis, and subsequent pathways related to these cascades, such as the aspartate-family pathway, are activated during germination. A relevant number of accumulated proteins and metabolites, especially in embryos, testifies the pivotal role of energetic supply in the preparation of plant growth. This article summarizes the key genetic pathways in embryo and endosperm during rice seed germination at the transcriptional, translational, and metabolite levels and thereby, emphasizes the value of combined multi-omics approaches to uncover the specific feature of tissues during germination.

Seed-derived defensins from Scots pine: structural and functional features

The recombinant PsDef5.1 defensin inhibits the growth of phytopathogenic fungi, Gram-positive and Gram-negative bacteria, and human pathogen Candida albicans. Expression of seed-derived Scots pine defensins is tissue-specific and developmentally regulated. Plant defensins are ubiquitous antimicrobial peptides that possess a broad spectrum of activities and multi-functionality. The genes for these antimicrobial proteins form a multigenic family in the plant genome and are expressed in every organ. Most of the known defensins have been isolated from seeds of various monocot and dicot species, but seed-derived defensins have not yet been characterized in gymnosperms. This study presents the isolation of two new 249 bp cDNA sequences from Scots pine seeds with 97.9% nucleotide homology named PsDef5.1 and PsDef5.2. Their deduced amino acid sequences have typical plant defensin features, including an endoplasmic reticulum signal sequence of 31 amino acids (aa), followed by a characteristic defensin domain of 51 aa. To elucidate the functional activity of new defensins, we expressed the mature form of PsDef5.1 in a prokaryotic system. The purified recombinant peptide exhibited activity against the phytopathogenic fungi and Gram-negative and Gram-positive bacteria with the IC₅₀ of 5-18 µM. Moreover, it inhibited the growth of the human pathogen Candida albicans with the IC₅₀ of 6.0 µM. Expression analysis showed that transcripts of PsDef5.1-2 genes were present in immature and mature pine seeds and different parts of seedlings at the early stage of germination. In addition, unlike the PsDef5.2, the PsDef5.1 gene was expressed in the reproductive organs. Our findings indicate that novel defensins are promising candidates for transgenic application and the development of new antimicrobial drugs.

Biocontrol Potential of Bacillus amyloliquefaciens against Botrytis pelargonii and Alternaria alternata on Capsicum annuum

The aim of this study was to assess the ability of Bacillus amyloliquefaciens, to augment plant growth and suppress gray mold and leaf spot in pepper plants. Morphological modifications in fungal pathogen hyphae that expanded toward the PGPR colonies were detected via scanning electron microscope. Furthermore, preliminary screening showed that PGPR could produce various hydrolytic enzymes in its media. Treatments with B. amyloliquefaciens suppressed Botrytis gray mold and Alternaria leaf spot diseases on pepper caused by Botrytis pelargonii and Alternaria alternata, respectively. The PGPR strain modulated plant physio-biochemical processes. The inoculation of pepper with PGPR decreased protein, amino acid, antioxidant, hydrogen peroxide, lipid peroxidation, and abscisic acid levels but increased salicylic acid and sugar levels compared to those of uninoculated plants, indicating a mitigation of the adverse effects of biotic stress. Moreover, gene expression studies confirmed physio-biochemical findings. PGPR inoculation led to increased expression of the CaXTH genes and decreased expression of CaAMP1, CaPR1, CaDEF1, CaWRKY2, CaBI-1, CaASRF1, CaSBP11, and CaBiP genes. Considering its beneficial effects, the inoculation of B. amyloliquefaciens can be proposed as an eco-friendly alternative to synthetic chemical fungicides.

Plant Defensins from a Structural Perspective

Plant defensins form a family of proteins with a broad spectrum of protective activities against fungi, bacteria, and insects. Furthermore, some plant defensins have revealed anticancer activity. In general, plant defensins are non-toxic to plant and mammalian cells, and interest in using them for biotechnological and medicinal purposes is growing. Recent studies provided significant insights into the mechanisms of action of plant defensins. In this review, we focus on structural and dynamics aspects and discuss structure-dynamics-function relations of plant defensins.

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.

Enhanced tolerance to Phytophthora root and stem rot by over-expression of the plant antimicrobial peptide CaAMP1 gene in soybean

BACKGROUND

Antimicrobial peptides play important roles in both plant and animal defense systems. Moreover, over-expression of CaAMP1 (Capsicum annuum antimicrobial protein 1), an antimicrobial protein gene isolated from C. annuum leaves infected with Xanthomonas campestris pv. vesicatoria, confers broad-spectrum resistance to hemibiotrophic bacterial and necrotrophic fungal pathogens in Arabidopsis. Phytophthora root and stem rot (PRR), caused by the fungus Phytophthora sojae, is one of the most devastating diseases affecting soybean (Glycine max) production worldwide.

RESULTS

In this study, CaAMP1 was transformed into soybean by Agrobacterium-mediated genetic transformation. Integration of the foreign gene in the genome of transgenic soybean plants and its expression at the translation level were verified by Southern and western blot analyses, respectively. CaAMP1 over-expression (CaAMP1-OX) lines inoculated with P. sojae race 1 exhibited enhanced and stable PRR tolerance through T2-T4 generations compared with the wild-type Williams 82 plants. Gene expression analyses in the transgenic plants revealed that the expression of salicylic acid-dependent, jasmonic acid-dependent, and plant disease resistance genes (R-genes) were significantly up-regulated after P. sojae inoculation.

CONCLUSIONS

These results indicate that CaAMP1 over-expression can significantly enhance PRR tolerance in soybean by eliciting resistance responses mediated by multiple defense signaling pathways. This provides an alternative approach for developing soybean varieties with improved tolerance against soil-borne pathogenic PRR.

Crystal structure of rice defensin OsAFP1 and molecular insight into lipid-binding

Defensins are antibacterial peptides that function in the innate immune system. OsAFP1, a defensin identified from Oryza sativa (rice), exhibits antimicrobial activity against rice pathogens. Intriguingly, OsAFP1 was also shown to demonstrate potent antifungal activity against the human pathogenic fungus Candida albicans by inducing apoptosis in target cells, suggesting that OsAFP1 represents a potential new antibiotic candidate; however, further analyses, particularly at the structural level, are required to elucidate the mechanistic underpinnings of OsAFP1 antifungal activity. Here, we determined the three-dimensional structure of OsAFP1 using X-ray crystallography. OsAFP1 features the cysteine-stabilized αβ structure highly conserved in plant defensins and presents a dimeric structure that appears necessary for antifungal activity. Superimposition of the OsAFP1 structure with that of Nicotiana alata NaD1 complexed with phosphatidic acid indicated that the target molecule is likely trapped between the S2-S3 loops of each OsAFP1 dimer. In lipid-binding analyses performed using nitrocellulose membranes immobilized with various membrane lipid components, OsAFP1 was found to bind to phosphatidylinositols (PIPs) harboring phosphate groups, particularly PI(3)P. These results indicate that OsAFP1 exerts antifungal activity by binding to PI(3)P contained in the C. albicans cell membrane, thereby applying cellular stress and inducing apoptosis. Furthermore, the OsAFP1 structure and site-specific-mutation analyses revealed that Arg1, His2, Leu4, Arg9, and Phe10 play critical roles in OsAFP1 dimer formation. Thus, our study provides novel insights into the antifungal mechanism of OsAFP1.

Mechanisms of Rice Endophytic Bradyrhizobial Cell Differentiation and Its Role in Nitrogen Fixation

Bradyrhizobium sp. strain SUTN9-2 is a symbiotic and endophytic diazotrophic bacterium found in legume and rice plants and has the potential to promote growth. The present results revealed that SUTN9-2 underwent cell enlargement, increased its DNA content, and efficiently performed nitrogen fixation in response to rice extract. Some factors in rice extract induced the expression of cell cycle and nitrogen fixation genes. According to differentially expressed genes (DEGs) from the transcriptomic analysis, SUTN9-2 was affected by rice extract and the deletion of the bclA gene. The up-regulated DEGs encoding a class of oxidoreductases, which act with oxygen atoms and may have a role in controlling oxygen at an appropriate level for nitrogenase activity, followed by GroESL chaperonins are required for the function of nitrogenase. These results indicate that following its exposure to rice extract, nitrogen fixation by SUTN9-2 is induced by the collective effects of GroESL and oxidoreductases. The expression of the sensitivity to antimicrobial peptides transporter (sapDF) was also up-regulated, resulting in cell differentiation, even when bclA (sapDF) was mutated. This result implies similarities in the production of defensin-like antimicrobial peptides (DEFs) by rice and nodule-specific cysteine-rich (NCR) peptides in legume plants, which affect bacterial cell differentiation.

A novel recombinant javanicin with dual antifungal and anti-proliferative activities

Resistance to common drugs by microorganisms and cancers has become a major issue in modern healthcare, increasing the number of deaths worldwide. Novel therapeutic agents with a higher efficiency and less side effects for the treatment of certain diseases are urgently needed. Plant defensins have an integral role in a hosts' immune system and are attractive candidates for combatting drug-resistant microorganisms. Interestingly, some of these defensins also showed great potential due to their cytotoxic activity toward cancer cells. In this study, a defensin encoding gene was isolated from five legume seeds using 3' rapid amplification of cDNA ends (3' RACE) with degenerate primers and cDNA cloning strategies. Bioinformatic tools were used for in silico identification and the characterization of new sequences. To study the functional characteristics of these unique defensins, the gene encoded for Sesbania javanica defensin, designated as javanicin, was cloned into pTXB-1 plasmid and expressed in the Escherichia coli Origami 2 (DE3) strain. Under optimized conditions, a 34-kDa javanicin-intein fusion protein was expressed and approximately 2.5-3.5 mg/L of soluble recombinant javanicin was successfully extracted with over 90% purity. Recombinant javanicin displayed antifungal properties against human pathogenic fungi, including resistant strains, as well as cytotoxic activities toward the human breast cancer cell lines, MCF-7 & MDA-MB-231. Recombinant javanicin holds great promise as a novel therapeutic agent for further medical applications.

Improved gene co-expression network quality through expression dataset down-sampling and network aggregation

Large-scale gene co-expression networks are an effective methodology to analyze sets of co-expressed genes and discover new gene functions or associations. Distances between genes are estimated according to their expression profiles and are visualized in networks that may be further partitioned to reveal communities of co-expressed genes. Creating expression profiles is now eased by the large amounts of publicly available expression data (microarrays and RNA-seq). Although many distance calculation methods have been intensively compared and reviewed in the past, it is unclear how to proceed when many samples reflecting a wide range of different conditions are available. Should as many samples as possible be integrated into network construction or be partitioned into smaller sets of more related samples? Previous studies have indicated a saturation in network performances to capture known associations once a certain number of samples is included in distance calculations. Here, we examined the influence of sample size on co-expression network construction using microarray and RNA-seq expression data from three plant species. We tested different down-sampling methods and compared network performances in recovering known gene associations to networks obtained from full datasets. We further examined how aggregating networks may help increase this performance by testing six aggregation methods.

Antibacterial Activity of Plant Defensins

Plant defensins are antimicrobial host defense peptides expressed in all higher plants. Performing a significant role in plant innate immunity, plant defensins display potent activity against a wide range of pathogens. Vertebrate and invertebrate defensins have well-characterized antibacterial activity, but plant defensins are commonly considered to display antimicrobial activity against only fungi. In this review, we highlight the often-overlooked antibacterial activity of plant defensins. Also, we illustrate methods to evaluate defensins for antibacterial activity and describe the current advances in uncovering their antibacterial modes of action.

Defensin-like peptides in wheat analyzed by whole-transcriptome sequencing: a focus on structural diversity and role in induced resistance

Antimicrobial peptides (AMPs) are the main components of the plant innate immune system. Defensins represent the most important AMP family involved in defense and non-defense functions. In this work, global RNA sequencing and de novo transcriptome assembly were performed to explore the diversity of defensin-like (DEFL) genes in the wheat Triticum kiharae and to study their role in induced resistance (IR) mediated by the elicitor metabolites of a non-pathogenic strain FS-94 of Fusarium sambucinum. Using a combination of two pipelines for DEFL mining in transcriptome data sets, as many as 143 DEFL genes were identified in T. kiharae, the vast majority of them represent novel genes. According to the number of cysteine residues and the cysteine motif, wheat DEFLs were classified into ten groups. Classical defensins with a characteristic 8-Cys motif assigned to group 1 DEFLs represent the most abundant group comprising 52 family members. DEFLs with a characteristic 4-Cys motif CX{3,5}CX{8,17}CX{4,6}C named group 4 DEFLs previously found only in legumes were discovered in wheat. Within DEFL groups, subgroups of similar sequences originated by duplication events were isolated. Variation among DEFLs within subgroups is due to amino acid substitutions and insertions/deletions of amino acid sequences. To identify IR-related DEFL genes, transcriptional changes in DEFL gene expression during elicitor-mediated IR were monitored. Transcriptional diversity of DEFL genes in wheat seedlings in response to the fungus Fusarium oxysporum, FS-94 elicitors, and the combination of both (elicitors + fungus) was demonstrated, with specific sets of up- and down-regulated DEFL genes. DEFL expression profiling allowed us to gain insight into the mode of action of the elicitors from F. sambucinum. We discovered that the elicitors up-regulated a set of 24 DEFL genes. After challenge inoculation with F. oxysporum, another set of 22 DEFLs showed enhanced expression in IR-displaying seedlings. These DEFLs, in concert with other defense molecules, are suggested to determine enhanced resistance of elicitor-pretreated wheat seedlings. In addition to providing a better understanding of the mode of action of the elicitors from FS-94 in controlling diseases, up-regulated IR-specific DEFL genes represent novel candidates for genetic transformation of plants and development of pathogen-resistant crops.

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.

Rice Defensin OsAFP1 is a New Drug Candidate against Human Pathogenic Fungi

Fungal infections, such as candidiasis and aspergillosis, are some of the most frequent infections in humans. Although antifungal drugs are available for the treatment of these infections, antifungal agents with new mechanisms of action should be developed because of the increasing incidence of drug-resistant pathogens in recent years. In this study, a basic functional analysis of rice defensin OsAFP1, a novel antifungal drug candidate, was conducted. OsAFP1 exerted fungicidal activity against Candida albicans, the most common pathogenic fungus in humans, at 4 μM concentration, but it did not inhibit the growth of human pathogenic bacteria. In addition, OsAFP1 retained structural stability after heat treatment at 100 °C for 10 min and after serum treatment at 37 °C for 24 h. A propidium iodide (PI) uptake assay and mutational analysis revealed that amino acid residues within the C-terminal γ-core motif of OsAFP1, particularly Leu-39 and Lys-41, play an important role in its antifungal activity. Further, PI uptake and apoptosis assays suggested that OsAFP1 exerts its antifungal activity by inducing apoptosis of target cells. Immunohistochemistry showed that the OsAFP1 target molecule was located in the cell wall. These findings indicate that OsAFP1 may be developed into a potent antifungal drug.

Nitric oxide promotes cancer cell dedifferentiation by disrupting an Oct4:caveolin-1 complex: A new regulatory mechanism for cancer stem cell formation

Cancer stem cells (CSCs) are unique populations of cells that can self-renew and generate different cancer cell lineages. Although CSCs are believed to be a promising target for novel therapies, the specific mechanisms by which these putative therapeutics could intervene are less clear. Nitric oxide (NO) is a biological mediator frequently up-regulated in tumors and has been linked to cancer aggressiveness. Here, we search for targets of NO that could explain its activity. We find that it directly affects the stability and function of octamer-binding transcription factor 4 (Oct4), known to drive the stemness of lung cancer cells. We demonstrated that NO promotes the CSC-regulatory activity of Oct4 through a mechanism that involves complex formation between Oct4 and the scaffolding protein caveolin-1 (Cav-1). In the absence of NO, Oct4 forms a molecular complex with Cav-1, which promotes the ubiquitin-mediated proteasomal degradation of Oct4. NO promotes Akt-dependent phosphorylation of Cav-1 at tyrosine 14, disrupting the Cav-1:Oct4 complex. Site-directed mutagenesis and computational modeling studies revealed that the hydroxyl moiety at tyrosine 14 of Cav-1 is crucial for its interaction with Oct4. Both removal of the hydroxyl via mutation to phenylalanine and phosphorylation lead to an increase in binding free energy (ΔG_bind) between Oct4 and Cav-1, destabilizing the complex. Together, these results unveiled a novel mechanism of CSC regulation through NO-mediated stabilization of Oct4, a key stem cell transcription factor, and point to new opportunities to design CSC-related therapeutics.

Heterologous expression and antimicrobial activity of OsGASR3 from rice (Oryza sativa L.)

According to an in silico analysis, OsGASR3 (LOC_Os03g55290) from rice (Oryza sativa L.) was predicted to be involved in plant defense mechanisms. A semi-quantitative reverse transcription polymerase chain reaction assay revealed that OsGASR3 is highly expressed in the inflorescences of Thai jasmine rice (O. sativa L. subsp. indica 'KDML 105'). To characterize the biological activity of OsGASR3, we produced an OsGASR3-glutathione S-transferase fusion protein in Escherichia coli Rosetta-gami (DE3) cells for a final purified recombinant OsGASR3 yield of 0.65 mg/L. The purified OsGASR3 inhibited the hyphal growth of Fusarium oxysporum f.sp. cubense and Helminthosporium oryzae at a relatively low concentration (7.5 μg/mL). Furthermore, OsGASR3 exhibited in planta inhibitory activity against Xanthomonas campestris, suggesting its involvement in defense mechanisms, in addition to its previously reported functions affecting growth and development. These observations indicate that recombinant OsGASR3 may be useful for protecting agriculturally important crops against pathogenic microbes.

Gene expression analysis, subcellular localization, and in planta antimicrobial activity of rice (Oryza sativa L.) defensin 7 and 8

Defensins are a group of plant antimicrobial peptides. In a previous study, it was reported that two recombinant rice (Oryza sativa L.) defensin (OsDEF) genes (OsDEF7 and OsDEF8) produced heterologously by bacteria inhibited the growth of several phytopathogen. Here, we analyzed gene expression patterns in Thai jasmine rice (O. sativa L. ssp. indica 'KDML 105') using quantitative reverse transcription-polymerase chain reaction and compared them with those in Japanese rice (O. sativa L. ssp. japonica 'Nipponbare'). Although the cultivars exhibited similar gene expression patterns at the developmental stages examined, the expression levels differed between organs. Upon Xanthomonas oryzae pv. oryzae infection in the leaves, both OsDEFs were highly upregulated at 8 days post-infection, suggesting that they play a role in pathogen defense. Moreover, in silico analyses revealed that OsDEF expression levels were affected by drought, cold, imbibition, anoxia, and dehydration stress. Using green fluorescent protein (GFP) fusions, we found that both OsDEFs were in the extracellular compartment, confirming their functions against pathogen infection. However, when recombinant OsDEFs (without GFP) were produced in tobacco BY-2 cells or Nicotiana benthamiana leaves, they could not be detected in either the culture medium or the cells. Yet, N. benthamiana leaves infiltrated with OsDEF7 or OsDEF8 constructs exhibited in planta inhibitory activity against the phytopathogen Xanthomonas campestris pv. glycines, suggesting that recombinant OsDEFs were present. Additionally, when targeting them to the ER compartment, recombinant OsDEFs could be detected. Lower inhibitory activity was observed when recombinant OsDEFs were targeted to the ER. These results suggest that OsDEFs play a role in controlling plant diseases.

Partial peptides from rice defensin OsAFP1 exhibited antifungal activity against the rice blast pathogen Pyricularia oryzae

Rice blast caused by Pyricularia oryzae is one of the most devastating diseases worldwide. This study aimed to investigate the antifungal activity of rice defensin OsAFP1 and its partial peptides against P. oryzae. The partial peptides near the N- and C-terminal regions of OsAFP1 exhibited approximately the same antifungal activity as the entire protein against P. oryzae. These partial peptides have the potential to be used as fungicides.

Antimicrobial peptides (AMPs): The quintessential 'offense and defense' molecules are more than antimicrobials

Antimicrobial peptides (AMPs) are cationic amphiphilic molecules with α-helix or β-sheet linear motifs and linear or cyclic configurations. For their role in 'defense and offense', they are present in all living organisms. AMPs are named so, as they inhibit a wide array of microbes by membrane pore formation and subsequent perturbation of mitochondrial membrane ionic balance. However, their functional repertoire is expanding with validated roles in cytotoxicity, wound healing, angiogenesis, apoptosis, and chemotaxis [1]. A number of endogenous AMPs have been characterized in human body such as defensins, cathelicidins, histatins etc. They mediate critical functions, but when homeostasis is broken, they turn hostile and initiate inflammatory diseases. This review discusses the sources of therapeutic AMPs; auto-immunity risks of endogenous AMPs, and their dermatological applications; normally overlooked risks of the peptides; and scopes ahead. This holistic work is expected to be a valuable reference for further research in this field.

Antibacterial activity and phospholipid recognition of the recombinant defensin J1-1 from Capsicum genus

The gene of the four disulfide-bridged defensin J1-1 from Capsicum was cloned into the expression vector pQE30 containing a 6His-tag as fusion protein. This construct was transfected into Origami strain of Escherichia coli and expressed after induction with isopropyl thiogalactoside (IPTG). The level of expression was 4 mg/L of culture medium, and the His-tagged recombinant defensin (HisXarJ1-1) was expressed exclusively into inclusion bodies. After solubilization, HisXarJ1-1 was purified by affinity and hydrophobic interaction chromatography. The reverse-phase HPLC profile of the HisXarJ1-1 product obtained from the affinity chromatography step showed single main peptide fraction of molecular masses of 7050.6 Da and after treatment with DTT a single fraction of 7, 042.6 Da corresponding to the reduced peptide was observed. An in vitro folding step of the HisXarJ1-1 generated a distinct profile of oxidized forms of the peptide this oxidized peptide was capable of binding phosphatidic acid in vitro. Possible dimer and oligomer of HisXarJ1-1 were visible in gel electrophoresis and immunodetected with anti-His antibodies. Pure recombinant defensin HisXarJ1-1 exhibited antibacterial activity against Pseudomonas aeruginosa.

Comparison of silicon nanoparticles and silicate treatments in fenugreek

Silicon (Si) fertilization improves crop cultivation and is commonly added in the form of soluble silicates. However, most natural plant-available Si originates from plant formed amorphous SiO₂ particles, phytoliths, similar to SiO₂-nanoparticles (SiNP). In this work we, therefore, compared the effect by sodium silicate and that of SiNP on Si accumulation, activity of antioxidative stress enzymes catalase, peroxidase, superoxide dismutase, lignification of xylem cell walls and activity of phenylalanine ammonia-lyase (PAL) as well as expression of genes for the putative silicon transporter (PST), defensive (Tfgd 1) and phosphoenolpyruvate carboxykinase (PEPCK) and protein in fenugreek (Trigonella foenum-graecum L.) grown in hydroponics. The results showed that Si was taken up from both silicate and SiNP treatments and increasing sodium silicate addition increased the translocation of Si to the shoot, while this was not shown with increasing SiNP addition. The silicon transporter PST was upregulated at a greater level when sodium silicate was added compared with SiNP addition. There were no differences in effects between sodium silicate and SiNP treatments on the other parameters measured. Both treatments increased the uptake and accumulation of Si, xylem cell wall lignification, cell wall thickness, PAL activity and protein concentration in seedlings, while there was no effect on antioxidative enzyme activity. Tfgd 1 expression was strongly downregulated in leaves at Si addition. The similarity in effects by silicate and SiNP would be due to that SiNP releases silicate, which may be taken up, shown by a decrease in SiNP particle size with time in the medium.