Recombinant expression, affinity purification and functional characterization of Scots pine defensin 1

Plant Defensin PgD1 a Biotechnological Alternative Against Plant Pathogens

Plant defensins are small antimicrobial proteins (AMP) that participate in the immune defense of plants through their antibacterial, antiviral and antifungal activities. PgD1 is a defensin from Picea glauca (Canadian Pine) and has antifungal activity against plant pathogens. This activity positions it as an alternative biotechnological agent to pesticides commonly used against these plant fungi diseases. The present study aimed to recombinantly produce PgD1 in Escherichia coli to characterize its in vitro antifungal potential against different phytopathogens. To achieve this, the coding gene was amplified and cloned into pET30a( +). Recombinant plasmid was subsequently introduced into E. coli for the soluble expression of defensin PgD1. To evaluate the antifungal activity of the expressed protein, the growth inhibition test was used in solid and liquid media for approximately 7 days against significant plant pathogens, that cause significant crop damage including: Botrytis cinerea, Colletotrichum gloeosporioides, Colletotrichum musae, Colletotrichum graminicola and Fusarium oxysporum. Additionally, stability assessments included temperature variation experiments and inhibition tests using dithiothreitol (DTT). The results showed that there was significant inhibition of the fungal species tested when in the presence of PgD1. Furthermore, defensin proved to be resistant to temperature variations and demonstrated that part of its stability is due to its primary structure rich in cysteine ​​residues through the denaturation test with dithiothreitol (DTT) where the antifungal activity of PgD1 defensin was inhibited. These data indicate that recombinant PgD1 could be utilized as a plant protection technology in agriculture.

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.

Defensin-like peptides from Capsicum chinense induce increased ROS, loss of mitochondrial functionality, and reduced growth of the fungus Colletotrichum scovillei

In the present study, we identified and characterized two defensin-like peptides in an antifungal fraction obtained from Capsicum chinense pepper fruits and inhibited the growth of Colletotrichum scovillei, which causes anthracnose. AMPs were extracted from the pericarp of C. chinense peppers and subjected to ion exchange, molecular exclusion, and reversed-phase in a high-performance liquid chromatography system. We investigated the endogenous increase in reactive oxygen species (ROS), the loss of mitochondrial functioning, and the ultrastructure of hyphae. The peptides obtained from the G3 fraction through molecular exclusion chromatography were subsequently fractionated using reverse-phase chromatography, resulting in the isolation of fractions F1, F2, F3, F4, and F5. The F1-Fraction suppressed C. scovillei growth by 90, 70.4, and 44% at 100, 50, and 25 μg mL-1, respectively. At 24 h, the IC50 and minimum inhibitory concentration were 21.5 μg mL-1 and 200 μg mL-1, respectively. We found an increase in ROS, which may have resulted in an oxidative burst, loss of mitochondrial functioning, and cytoplasm retraction, as well as an increase in autophagic vacuoles. MS/MS analysis of the F1-Fraction indicated the presence of two defensin-like proteins, and we were able to identify the expression of three defensin sequences in our C. chinense fruit extract. The F1-Fraction was also found to inhibit the activity of insect α-amylases. In summary, the F1-Fraction of C. chinense exhibits antifungal activity against a major pepper pathogen that causes anthracnose. These defensin-like compounds are promising prospects for further research into antifungal and insecticide biotechnology applications. © 2024 Society of Chemical Industry.

Bioinformatic analysis of wheat defensin gene family and function verification of candidate genes

Plant defensins are widely distributed in the leaves, fruits, roots, stems, seeds, and tubers. Research shows that defensin in plants play a significant role in physiological metabolism, growth and development. Plant defensins can kill and suppress a variety of pathogenic bacteria. In this study, we understand the phylogenetic relationships, protein characterization, chromosomal localization, promoter and gene structural features of the TaPDFs family through sequence alignment and conserved protein structural domain analysis. A total of 73 PDF gene members in wheat, 15 PDF genes in maize, and 11 PDF genes in rice were identified. A total of 35, 65, and 34 PDF gene members were identified in the genomes of Ae. tauschii, T. urartu, and T. dicoccoides, respectively. TaPDF4.9 and TaPDF2.15 were constructed into pART27 vector with YFP by homologous recombination for subcellular localization analysis. Subcellular localization results showed that TaPDF4.9 and TaPDF2.15 were basically located in the cell membrane and cytoplasm, and TaPDF4.9 was also located in the nucleus. TaPDF4.9 and TaPDF2.15 could inhibit the infection of Phytophthora infestans strain '88069'. The results suggest that TaPDFs may be able to improve disease resistance. The study of wheat defensins will be beneficial for improving wheat yield and provides a theoretical basis for research on resistance to wheat diseases.

Structure, dynamics, and function of PsDef2 defensin from Pinus sylvestris

Plant defensins demonstrate high structural stability at extreme temperatures and pH values and, in general, are non-toxic to mammalian cells. These properties make them attractive candidates for use in biotechnology and biomedicine. Knowing the structure-function relationship is desirable to guide the design of plant defensin-based applications. Thus far, the broad range of biological activities was described only for one defensin from gymnosperms, the defensin PsDef1 from Scots pine. Here, we report that closely related defensin from the same taxonomy group, PsDef2, differing from PsDef1 by six amino acids, also possesses antimicrobial, antibacterial, and insect α-amylase inhibitory activities. We also report the solution structure and dynamics properties of PsDef2 assessed using a combination of experimental nuclear magnetic resonance (NMR) techniques. Lastly, we perform a comparative analysis of PsDef2 and PsDef1 gaining a molecular-level insight into their structure-dynamics-function relationship.

Use of Defensins to Develop Eco-Friendly Alternatives to Synthetic Fungicides to Control Phytopathogenic Fungi and Their Mycotoxins

Crops are threatened by numerous fungal diseases that can adversely affect the availability and quality of agricultural commodities. In addition, some of these fungal phytopathogens have the capacity to produce mycotoxins that pose a serious health threat to humans and livestock. To facilitate the transition towards sustainable environmentally friendly agriculture, there is an urgent need to develop innovative methods allowing a reduced use of synthetic fungicides while guaranteeing optimal yields and the safety of the harvests. Several defensins have been reported to display antifungal and even-despite being under-studied-antimycotoxin activities and could be promising natural molecules for the development of control strategies. This review analyses pioneering and recent work addressing the bioactivity of defensins towards fungal phytopathogens; the details of approximately 100 active defensins and defensin-like peptides occurring in plants, mammals, fungi and invertebrates are listed. Moreover, the multi-faceted mechanism of action employed by defensins, the opportunity to optimize large-scale production procedures such as their solubility, stability and toxicity to plants and mammals are discussed. Overall, the knowledge gathered within the present review strongly supports the bright future held by defensin-based plant protection solutions while pointing out the obstacles that still need to be overcome to translate defensin-based in vitro research findings into commercial products.

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.

Chitosan increases Pinus pinaster tolerance to the pinewood nematode (Bursaphelenchus xylophilus) by promoting plant antioxidative metabolism

The pine wilt disease (PWD), for which no effective treatment is available at the moment, is a constant threat to Pinus spp. plantations worldwide, being responsible for significant economic and environmental losses every year. It has been demonstrated that elicitation with chitosan increases plant tolerance to the pinewood nematode (PWN) Bursaphelenchus xylophilus, the causal agent of the PWD, but the biochemical and genetic aspects underlying this response have not been explored. To understand the influence of chitosan in Pinus pinaster tolerance against PWN, a low-molecular-weight (327 kDa) chitosan was applied to mock- and PWN-inoculated plants. Nematode population, malondialdehyde (MDA), catalase, carotenoids, anthocyanins, phenolic compounds, lignin and gene expression related to oxidative stress (thioredoxin 1, TRX) and plant defence (defensin, DEF, and a-farnesene synthase, AFS), were analysed at 1, 7, 14, 21 and 28 days post-inoculation (dpi). At 28 dpi, PWN-infected plants elicited with chitosan showed a sixfold lower nematode population when compared to non-elicited plants. Higher levels of MDA, catalase, carotenoids, anthocyanins, phenolic compounds, and lignin were detected in chitosan-elicited plants following infection. The expression levels of DEF gene were higher in elicited plants, while TRX and AFS expression was lower, possibly due to the disease containment-effect of chitosan. Combined, we conclude that chitosan induces pine defences against PWD via modulation of metabolic and transcriptomic mechanisms related with plant antioxidant system.

A transcriptomic view to wounding response in young Scots pine stems

We studied the stress response of five-year-old Scots pine xylem to mechanical wounding using RNA sequencing. In general, we observed a bimodal response in pine xylem after wounding. Transcripts associated with water deficit stress, defence, and cell wall modification were induced at the earliest time point of three hours; at the same time, growth-related processes were down-regulated. A second temporal wave was triggered either at the middle and/or at the late time points (one and four days). Secondary metabolism, such as stilbene and lignan biosynthesis started one day after wounding. Scots pine synthesises the stilbenes pinosylvin and its monomethyl ether both as constitutive and induced defence compounds. Stilbene biosynthesis is induced by wounding, pathogens and UV stress, but is also developmentally regulated when heartwood is formed. Comparison of wounding responses to heartwood formation shows that many induced processes (in addition to stilbene biosynthesis) are similar and relate to defence or desiccation stress, but often specific transcripts are up-regulated in the developmental and wounding induced contexts. Pine resin biosynthesis was not induced in response to wounding, at least not during the first four days.

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.

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.

Gene isolation and structural characterization of a legume tree defensin with a broad spectrum of antimicrobial activity

The recombinant EcgDf1 defensin has an antimicrobial effect against both plant and human pathogens. In silico analyses predict that EcgDf1 is prone to form dimers capable of interacting with the membranes of microorganisms. Plant defensins comprise a large family of antimicrobial peptides (AMP) with a wide range of biological functions. They are cysteine-rich molecules, highly sequence diverse but with a conserved and stable structure. In this work, a defensin gene (EcgDf1) was isolated from Erythrina crista-galli, a legume tree native from South America. The predicted peptide presents eight cysteines, with a γ-core motif GXCX3-9C and six cysteines distributed like the typical defensin αβ motif. The mature EcgDf1 coding sequence was heterologously expressed in Escherichia coli strains and purified by affinity chromatography. Possible dimer and oligomers of EcgDf1 were visible in SDS electrophoresis. Moreover, its 3D structure, determined by homology modeling, docking, and molecular dynamics simulations, was found to be compatible with the formation of homodimers between the β3 and β1-loop-α1, leaving the β2-loop-β3 free to interact with lipid membranes. The purified recombinant peptide inhibited the growth of several critical plant and human pathogens, like the opportunistic fungi Candida albicans and Aspergillus niger and the plant pathogens Clavibacter michiganensis ssp. michiganensis, Penicillium expansum, Botrytis cinerea, and Alternaria alternata. EcgDf1 is a promising candidate for the development of antimicrobial products for use in agriculture and medicine.

Antimicrobial and structural insights of a new snakin-like peptide isolated from Peltophorum dubium (Fabaceae)

Snakins are antimicrobial peptides (AMPs) found, so far, exclusively in plants, and known to be important in the defense against a wide range of pathogens. Like other plant AMPs, they contain several positively charged amino acids, and an even number of cysteine residues forming disulfide bridges which are considered important for their usual function. Despite its importance, studies on snakin tertiary structure and mode of action are still scarce. In this study, a new snakin-like gene was isolated from the native plant Peltophorum dubium, and its expression was verified in seedlings and adult leaves. The deduced peptide (PdSN1) shows 84% sequence identity with potato snakin-1 mature peptide, with the 12 cysteines characteristic from this peptide family at the GASA domain. The mature PdSN1 coding sequence was successfully expressed in Escherichia coli. The purified recombinant peptide inhibits the growth of important plant and human pathogens, like the economically relevant potato pathogen Streptomyces scabies and the opportunistic fungi Candida albicans and Aspergillus niger. Finally, homology and ab initio modeling techniques coupled to extensive molecular dynamics simulations were used to gain insight on the 3D structure of PdSN1, which exhibited a helix-turn-helix motif conserved in both native and recombinant peptides. We found this motif to be strongly coded in the sequence of PdSN1, as it is stable under different patterns of disulfide bonds connectivity, and even when the 12 cysteines are considered in their reduced form, explaining the previous experimental evidences.

Antifungal plant defensins: mechanisms of action and production

Plant defensins are small, cysteine-rich peptides that possess biological activity towards a broad range of organisms. Their activity is primarily directed against fungi, but bactericidal and insecticidal actions have also been reported. The mode of action of various antifungal plant defensins has been studied extensively during the last decades and several of their fungal targets have been identified to date. This review summarizes the mechanism of action of well-characterized antifungal plant defensins, including RsAFP2, MsDef1, MtDef4, NaD1 and Psd1, and points out the variety by which antifungal plant defensins affect microbial cell viability. Furthermore, this review summarizes production routes for plant defensins, either via heterologous expression or chemical synthesis. As plant defensins are generally considered non-toxic for plant and mammalian cells, they are regarded as attractive candidates for further development into novel antimicrobial agents.

Design and high-level expression of a hybrid antimicrobial peptide LF15-CA8 in Escherichia coli

Antimicrobial peptides (AMPs) have been paid considerable attention owing to their broad-spectrum antimicrobial activity and have great potential as novel antimicrobials. In this study, a novel hybrid peptide LF15-CA8 was designed on the basis of bovine lactoferricin (LfcinB) and cecropin A. The gene segment encoding LF15-CA8 was synthesized and cloned into pGEX-4T-BH to form pGEX-4T-LC1 containing one copy of the LF15-CA8 coding region. A series of recombinant vectors containing up to six multiple-copy LF15-CA8 coding regions, i.e., pGEX-4T-LCn (n = 1–6), were subsequently constructed, and used for transformation in Escherichia coli BL21(DE3). After induction with IPTG, pGEX-4T-LC1 and pGEX-4T-LC2 transformants successfully expressed fusion proteins GST-LF15-CA8 and GST-(LF15-CA8)2 in the form of inclusion bodies, respectively. The inclusion bodies were dissolved and the peptide was successfully released in 70 % formic acid in a single step. After purification, about 10.0 mg of the recombinant peptide LF15-CA8 with purity more than 97 % was obtained from 1 l of bacteria culture of pGEX-4T-LC2 transformants. LF15-CA8 caused an increase in antibacterial activity against Gram-positive bacterium (Staphylococcus aureus ATCC 25923) compared with the parent peptides and did not show obvious hemolytic activity against human erythrocytes in the range of effective antibacterial concentration. These results suggest that the peptide LF15-CA8 could be a promising candidate for therapeutic applications, and may lead to a cost-effective solution for the large-scale production of AMPs.

Tandem combination of Trigonella foenum-graecum defensin (Tfgd2) and Raphanus sativus antifungal protein (RsAFP2) generates a more potent antifungal protein

Plant defensins are small (45 to 54 amino acids) positively charged antimicrobial peptides produced by the plant species, which can inhibit the growth of a broad range of fungi at micro-molar concentrations. These basic peptides share a common characteristic three-dimensional folding pattern with one α-helix and three β-sheets that are stabilized by eight disulfide-linked cysteine residues. Instead of using two single-gene constructs, it is beneficial when two effective genes are made into a single fusion gene with one promoter and terminator. In this approach, we have linked two plant defensins namely Trigonella foenum-graecum defensin 2 (Tfgd2) and Raphanus sativus antifungal protein 2 (RsAFP2) genes by a linker peptide sequence (occurring in the seeds of Impatiens balsamina) and made into a single-fusion gene construct. We used pET-32a+ vector system to express Tfgd2-RsAFP2 fusion gene with hexahistidine tag in Escherichia coli BL21 (DE3) pLysS cells. Induction of these cells with 1 mM IPTG achieved expression of the fusion protein. The solubilized His6-tagged recombinant fusion protein was purified by immobilized-metal (Ni2+) affinity column chromatography. The final yield of the fusion protein was 500 ng/μL. This method produced biologically active recombinant His6-tagged fusion protein, which exhibited potent antifungal action towards the plant pathogenic fungi (Botrytis cinerea, Fusarium moniliforme, Fusarium oxysporum, Phaeoisariopsis personata and Rhizoctonia solani along with an oomycete pathogen Phytophthora parasitica var nicotianae) at lower concentrations under in vitro conditions. This strategy of combining activity of two defensin genes into a single-fusion gene will definitely be a promising utility for biotechnological applications.

Impact of SO(2) on Arabidopsis thaliana transcriptome in wildtype and sulfite oxidase knockout plants analyzed by RNA deep sequencing

High concentrations of sulfur dioxide (SO(2) ) as an air pollutant, and its derivative sulfite, cause abiotic stress that can lead to cell death. It is currently unknown to what extent plant fumigation triggers specific transcriptional responses. To address this question, and to test the hypothesis that sulfite oxidase (SO) is acting in SO(2) detoxification, we compared Arabidopsis wildtype (WT) and SO knockout lines (SO-KO) facing the impact of 600 nl l(-1) SO(2) , using RNAseq to quantify absolute transcript abundances. These transcriptome data were correlated to sulfur metabolism-related enzyme activities and metabolites obtained from identical samples in a previous study. SO-KO plants exhibited remarkable and broad regulative responses at the mRNA level, especially in transcripts related to sulfur metabolism enzymes, but also in those related to stress response and senescence. Focusing on SO regulation, no alterations were detectable in the WT, whereas in SO-KO plants we found up-regulation of two splice variants of the SO gene, although this gene is not functional in this line. Our data provide evidence for the highly specific coregulation between SO and sulfur-related enzymes like APS reductase, and suggest two novel candidates for involvement in SO(2) detoxification: an apoplastic peroxidase, and defensins as putative cysteine mass storages.

Cytoplasmic expression, antibody production, and characterization of the novel zinc finger protein 637

Zinc finger protein 637 (zfp637), belonging to the Kruppel-like protein family, comprises one atypical C(2)H(2) and six consecutive typical zinc finger motifs. Based on the structural characterization of zfp637 and its location in the cell nucleus, we predict that zfp637 might function as a DNA-binding protein to regulate gene transcription. However, the absence of both a purified zfp637 protein and any commercial antibody for detecting it in cells and tissues has limited functional studies of zfp637 to date. Here, we developed and optimized an expression system by fusing zfp637 with glutathione S-transferase (GST) to achieve a maximal yield of soluble GST-zfp637 fusion protein in Escherichia coli BL21(DE3) cells. The yield was about 10 mg/l of the original bacterial culture. The recombinant GST-zfp637 fusion protein was purified and used for polyclonal antibody production in rabbits. In addition, we developed a method to remove the anti-GST antibody component and obtained a highly purified anti-zfp637 antibody, as demonstrated by an enzyme-linked immunosorbent assay. Western blotting showed that the anti-zfp637 antibody recognized not only the recombinant zfp637 protein but also endogenous zfp637 in several cell lines. The protein was localized mainly in the cell nucleus by immunofluorescence and immunohistochemistry. The expression levels of zfp637 mRNA and protein were significantly increased in NIH3T3 cells treated with 200 μM of H(2)O(2) in a time-dependent manner. The recombinant GST-zfp637 fusion protein and our purified anti-zfp637 antibody will help in elucidating the function of zfp637.

Oral administration of recombinant epinecidin-1 protected grouper (Epinephelus coioides) and zebrafish (Danio rerio) from Vibrio vulnificus infection and enhanced immune-related gene expressions

Immunostimulatory effects of the oral administration of the recombinant epinecidin-1 protein from BL21 Escherichia coli (containing the pET28a-epinecidin-1-dsRed plasmid) were studied in grouper (Epinephelus coioides) and zebrafish (Danio rerio). For this purpose, fish were fed diets for 30 days containing the recombinant epinecidin-1 protein from BL21 E. coli (containing the pET28a-epinecidin-1-dsRed plasmid) at different bacterial numbers (10(4), 10(6), 10(8), and 10(10) colony-forming units (cfu) of BL21 E. coli in 50 ml of LB medium) mixed with 50 g of eel powder as fodder. After 30 days of feeding, immune-related gene expressions for bacterial-infection responses and disease resistance against Vibrio vulnificus (204) were determined. The V. vulnificus (204) injected into the fish abdominal cavity mimicked gram-negative bacterial infections in culture ponds. Experimental results assessed whether the recombinant epinecidin-1 protein from BL21 E. coli (containing the pET28a-epinecidin-1-dsRed plasmid) has up- (or down-) regulation immune-related genes expression. Results indicated that the recombinant epinecidin-1 protein from BL21 E. coli administered as a feed supplement significantly enhanced expressions several immune-related genes such as tumor necrosis factor (TNF)-1 in grouper and Toll-like receptor (TLR)4, interleukin (IL)-1β, nitric oxide synthase (NOS)2, and nuclear factor (NF)-κB in zebrafish. After being challenged with V. vulnificus (204) for 24, 48, 72, or 96 h, the percentage mortality was significantly reduced in treated fish, which indicated that the recombinant epinecidin-1 protein from BL21 E. coli administered as a feed supplement could bring about downregulation of TNF-1 expression and functioned like an antagonist for binding TLR4, which reduced the signal transduction pathway for inhibiting TNF and IL-1β expressions while reducing binding of the transcription factor, NF-κB, to TNF and the IL-1β promoter region. The experimental results indicated that dietary intake of the recombinant epinecidin-1 protein from BL21 E. coli modulated immune-related gene expressions and disease resistance of grouper and zebrafish after a V. vulnificus (204) infection.

Molecular cloning and functional analysis of a recombinant ribosome-inactivating protein (alpha-momorcharin) from Momordica charantia

Alpha-momorcharin (α-MC), a member of the ribosome-inactivating protein (RIP) family, has been used not only as antiviral, antimicrobial, and antitumor agents, but also as toxicant to protozoa, insects, and fungi. In this study, we expressed the protein in Escherichia coli Rosetta (DE3) pLysS strain and purified it by nickel-nitrilotriacetic acid affinity chromatography. A total of 85 mg of homogeneous protein was obtained from 1 l culture supernatant of Rosetta (DE3) pLysS, showing a high recovery rate of 73.9%. Protein activity assay indicated that α-MC had both N-glycosidase activity and DNA-nuclease activity, the former releasing RIP diagnostic RNA fragment (Endo's fragment) from rice rRNAs and the latter converting supercoiled circular DNA of plasmid pET-32a(+) into linear conformations in a concentration-dependent manner. Specially, we found that α-MC could inhibit the mycelial growth of Fusarium solani and Fusarium oxysporum with IC(50) values of 6.23 and 4.15 μM, respectively. Results of optical microscopy and transmission electron microscopy demonstrated that α-MC caused extensive septum formation, loss of integrity of the cell wall, separation of the cytoplasm from the cell wall, deformation of cells with irregular budding sites, and apoptosis in F. solani. Moreover, α-MC was active against Pseudomonas aeruginosa with an IC(50) value of 0.59 μM. The α-MC protein carries a high potential for the design of new antifungal drugs or the development of transgenic crops resistant to pathogens.

Four plant defensins from an indigenous South African Brassicaceae species display divergent activities against two test pathogens despite high sequence similarity in the encoding genes

BACKGROUND

Plant defensins are an important component of the innate defence system of plants where they form protective antimicrobial barriers between tissue types of plant organs as well as around seeds. These peptides also have other activities that are important for agricultural applications as well as the medical sector. Amongst the numerous plant peptides isolated from a variety of plant species, a significant number of promising defensins have been isolated from Brassicaceae species. Here we report on the isolation and characterization of four defensins from Heliophila coronopifolia, a native South African Brassicaceae species.

RESULTS

Four defensin genes (Hc-AFP1-4) were isolated with a homology based PCR strategy. Analysis of the deduced amino acid sequences showed that the peptides were 72% similar and grouped closest to defensins isolated from other Brassicaceae species. The Hc-AFP1 and 3 peptides shared high homology (94%) and formed a unique grouping in the Brassicaceae defensins, whereas Hc-AFP2 and 4 formed a second homology grouping with defensins from Arabidopsis and Raphanus. Homology modelling showed that the few amino acids that differed between the four peptides had an effect on the surface properties of the defensins, specifically in the alpha-helix and the loop connecting the second and third beta-strands. These areas are implicated in determining differential activities of defensins. Comparing the activities after recombinant production of the peptides, Hc-AFP2 and 4 had IC50 values of 5-20 μg ml-1 against two test pathogens, whereas Hc-AFP1 and 3 were less active. The activity against Botrytis cinerea was associated with membrane permeabilization, hyper-branching, biomass reduction and even lytic activity. In contrast, only Hc-AFP2 and 4 caused membrane permeabilization and severe hyper-branching against the wilting pathogen Fusarium solani, while Hc-AFP1 and 3 had a mild morphogenetic effect on the fungus, without any indication of membrane activity. The peptides have a tissue-specific expression pattern since differential gene expression was observed in the native host. Hc-AFP1 and 3 expressed in mature leaves, stems and flowers, whereas Hc-AFP2 and 4 exclusively expressed in seedpods and seeds.

CONCLUSIONS

Two novel Brassicaceae defensin sequences were isolated amongst a group of four defensin encoding genes from the indigenous South African plant H. coronopifolia. All four peptides were active against two test pathogens, but displayed differential activities and modes of action. The expression patterns of the peptide encoding genes suggest a role in protecting either vegetative or reproductive structures in the native host against pathogen attack, or roles in unknown developmental and physiological processes in these tissues, as was shown with other defensins.