Osmotin from Calotropis procera latex: new insights into structure and antifungal properties

Review: Laticifer as a plant defense mechanism

Laticifers have been utilized as paradigms to enhance comprehension of specific facets of plant ecology and evolution. From the beginning of seedling growth, autonomous laticifer networks are formed throughout the plant structure, extending across all tissues and organs. The vast majority of identified products resulting from laticifer chemistry and metabolism are linked to plant defense. The latex, which is the fluid contained within laticifers, is maintained under pressure and has evolved to serve as a defense mechanism against both aggressors and invaders, irrespective of their capabilities or tactics. Remarkably, the latex composition varies among different species. The current goal is to understand the specific functions of various latex components in combating plant enemies. Therefore, the study of latex's chemical composition and proteome plays a critical role in advancing our understanding about plant defense mechanisms. Here, we will discuss some of these aspects.

Efficacy of maturase K and rpL20 protein extracted from C. procera leaves on Anophelesstephensi

The present work is carried out to protein isolation, purification, and characterization from leaves, stem, and seed of C. procera and to evaluate the larvicidal potential on Anopheles stephensi. The whole protein was isolated using protein extraction buffer and precipitated by ammonium sulphate and larvicidal active protein was purified by the column chromatography. The homogeneity of larvicidal protein was confirmed by the SDS-PAGE. The identification of protein was done by the HPLC and LC-MS/ESI-MS. The crude protein from leaves showed 100% mortality of 3rd instar larvae of An. stephensi at the concentration of 5.5 mg/ml after 24 h of exposure. The crude protein from stem showed 25% mortality and no mortality observed was observed in seed protein. The leaves crude protein was further purified by ion exchange chromatography and eluted fractions were tested for larvicidal potential. The purified single protein fractions L2 and L3 from C. procera leaves showed 100% mortality at concentration of 0.06 mg/ml. The homogeneity of purified protein was confirmed by SDS-PAGE and two bands of 26 kDa and 15 kDa protein were observed. The peptide sequence "R.SQMLENSFLIENVMKR.L" was identified in the trypsin digested homogenous protein fraction L2 and "R.DRGSQKR.N" peptide sequence in L3 fraction by LC-MS/ESI-MS. The CprL2 peptide showed the sequence similarity with the protein maturase K and CprL3 peptide showed the sequence similarity with ribosomal protein L20 of C. procera. The conserved functional domain was also identified in both the CprL2 and CprL3 peptide. The identified proteins showed strong larvicidal efficacy at very low concentration. The identified proteins are novel and natural larvicidal agents against An. stephensi and hence can be used to control the malaria.

Novel Multiresistant Osmotin-like Protein from Sweetpotato as a Promising Biofungicide to Control Ceratocystis fimbriata by Destroying Spores through Accumulation of Reactive Oxygen Species

Osmotin-like proteins (OLPs) play an important role in host-plant defense. In this study, a novel multiresistant OLP (IbOLP1) was screened from sweetpotato (Ipomoea batatas) with a molecular weight of 26.3 kDa. The expression level of IbOLP1 was significantly higher in resistant cultivars than susceptible ones after inoculation with Ceratocystis fimbriata, which causes black rot disease in sweetpotato. The expression of IbOLP1 in Pichia pastoris led to the lysis of yeast cells themselves. The recombinant IbOLP1 displayed antifungal, antibacterial, and antinematode activity and stability. IbOLP1 could restrain the mycelial growth and lyse spores of C. fimbriata, distinctly reducing the incidence of black rot in sweetpotato. The IbOLP1 can trigger the apoptosis of black rot spores by elevating the intracellular levels of reactive oxygen species. Collectively, these findings suggest that IbOLP1 can be used to develop natural antimicrobial resources instead of chemical agents and generate new, disease-resistant germplasm.

Proteomic analysis of Cryptostegia grandiflora latex, purification, characterization, and biological activity of two osmotin isoforms

Although latex fluids are found in >20,000 plant species, the biochemical composition and biological function of their proteins are still poorly explored. Thus, this work aimed to conduct a proteomic analysis of Cryptostegia grandiflora latex (CgLP) for subsequent purification and characterization of an antifungal protein. After 2D-SDS-PAGE and mass spectrometry, 27 proteins were identified in CgLP, including a polygalacturonase inhibitor, cysteine peptidases, pathogenesis-related proteins (PR-4), and osmotins. Then, two osmotin isoforms (CgOsm) were purified, and a unique N-terminal sequence was determined (1ATFDIRSNCPYTVWAAAVPGGGRRLDRGQTWTINVAPGTA40). The PCR products revealed a cDNA sequence of 609 nucleotides for CgOsm, which encoded a polypeptide with 203 amino acid residues. The structure of CgOsm has features of typical osmotin or thaumatin-like proteins (TLPs), such as 16 conserved Cys residues, REDDD and FF motifs, an acidic cleft, and three main domains. Atomic force microscopy (AFM) and bioinformatics suggested that CgOsm is associated with three chain units. This result was interesting since the literature describes osmotins and TLPs as monomers. AFM also showed that Fusarium falciforme spores treated with CgOsm were drastically damaged. Therefore, it is speculated that CgOsm forms pores in the membrane of these cells, causing the leakage of cytoplasmic content.

Various Biomimetics, Including Peptides as Antifungals

Biomimetics, which are similar to natural compounds that play an important role in the metabolism, manifestation of functional activity and reproduction of various fungi, have a pronounced attraction in the current search for new effective antifungals. Actual trends in the development of this area of research indicate that unnatural amino acids can be used as such biomimetics, including those containing halogen atoms; compounds similar to nitrogenous bases embedded in the nucleic acids synthesized by fungi; peptides imitating fungal analogs; molecules similar to natural substrates of numerous fungal enzymes and quorum-sensing signaling molecules of fungi and yeast, etc. Most parts of this review are devoted to the analysis of semi-synthetic and synthetic antifungal peptides and their targets of action. This review is aimed at combining and systematizing the current scientific information accumulating in this area of research, developing various antifungals with an assessment of the effectiveness of the created biomimetics and the possibility of combining them with other antimicrobial substances to reduce cell resistance and improve antifungal effects.

Genome-wide characterization and expression of the TLP gene family associated with Colletotrichum gloeosporioides inoculation in Fragaria × ananassa

Background

Colletotrichum gloeosporioides, a soil-borne fungal pathogen, causes significant yield losses in many plants, including cultivated strawberry (Fragaria × ananassa, 2n = 8x = 56). Thaumatin-like proteins (TLPs) are a large and complex family of proteins that play a vital role in plant host defense and other physiological processes.

Methods

To enhance our understanding of the antifungal activity of F. × ananassa TLPs (FaTLP), we investigated the genome-wide identification of FaTLP gene families and their expression patterns in F. × ananassa plants upon pathogen infection. Moreover, we used RNA sequencing (RNA-seq) to detect the differences in the expression patterns of TLP genes between different resistant strawberry cultivars in response to C. gloeosporioides infection.

Results

In total, 76 TLP genes were identified from the octoploid cultivated strawberry genome with a mean length of 1,439 bp. They were distributed on 24 F. × ananassa chromosomes. The FaTLP family was then divided into ten groups (Group I-X) according to the comparative phylogenetic results. Group VIII contained the highest number of TLP family genes. qRT-PCR analysis results indicated that FaTLP40, FaTLP41, FaTLP43, FaTLP68, and FaTLP75 were upregulated following C. gloeosporioides infection in the resistant octoploid strawberry.

Conclusions

The data showed some differences in TLP gene expression patterns across different resistant strawberry cultivars, as well as faster TLP defense responses to pathogenic fungi in resistant cultivars. This study will aid in the characterization of TLP gene family members found in octoploid strawberries and their potential biological functions in plants' defenses against pathogenic fungi.

A review on phytochemical constituents and pharmacological potential of Calotropis procera

Calotropis procera is locally known as Aak or Madar in Hindi, milk weed in English and belongs to the family Apocynaceae and subfamily Asclepiadoideae. Although a wasteland plant, it is of sacred use as its flowers are offered for worshipping Lord Shiva, a Hindu God. Tribes all over the world use the plant in treatment of various diseases like snake bite, body pain, asthma, epilepsy, cancer, sexual disorders, skin diseases and many more. This plant contains various phytoconstituents such as flavonoids, terpenoids, cardenolides, steroids oxypregnanes etc. Though literature searches reveal many reviews about ethnomedicinal uses, chemical composition and pharmacological activities, no recent papers are available that provide an overview of the therapeutic potential and toxicity of Calotropis procera. Hence, the insight of this review is to provide a systemic summary of phytochemistry, pharmacology, toxicology and therapeutic potential of Calotropis procera and to highlight the gaps in the knowledge so as to offer inspiration for future research.

Calotropis procera is also known as Aak or Madar. The present review provides a systematic outline of phytochemistry, toxicology, pharmacology and therapeutic potential of Calotropis procera.

An Overview of the Characteristics and Potential of Calotropis procera From Botanical, Ecological, and Economic Perspectives

Calotropis procera (Aiton) Dryand. (commonly known as the apple of sodom, calotrope, and giant milkweed) is an evergreen, perennial shrub of the family Apocynaceae, mainly found in arid and semi-arid regions. It is a multipurpose plant, which can be utilized for medicine, fodder, and fuel purposes, timber and fiber production, phytoremediation, and synthesis of nanoparticles. It has been widely used in traditional medicinal systems across North Africa, Middle East Asia, and South-East Asia. At present, it is being extensively explored for its potential pharmacological applications. Several reports also suggest its prospects in the food, textile, and paper industries. Besides, C. procera has also been acknowledged as an ornamental species. High pharmacological potential and socio-economic value have led to the pantropical introduction of the plant. Morpho-physiological adaptations and the ability to tolerate various abiotic stresses enabled its naturalization beyond the introduced areas. Now, it is recognized as an obnoxious environmental weed in several parts of the world. Its unnatural expansion has been witnessed in the regions of South America, the Caribbean Islands, Australia, the Hawaiian Islands, Mexico, Seychelles, and several Pacific Islands. In Australia, nearly 3.7 million hectares of drier areas, including rangelands and Savannahs, have been invaded by the plant. In this review, multiple aspects of C. procera have been discussed including its general characteristics, current and potential uses, and invasive tendencies. The objectives of this review are a) to compile the information available in the literature on C. procera, to make it accessible for future research, b) to enlist together its potential applications being investigated in different fields, and c) to acknowledge C. procera as an emerging invasive species of arid and semi-arid regions.

Osmotin-Like Protein Gene from Panax notoginseng Is Regulated by Jasmonic Acid and Involved in Defense Responses to Fusarium solani

Osmotin and osmotin-like proteins (OLPs) play important roles in plant defense responses. The full-length cDNA sequence of an OLP gene was cloned from Panax notoginseng using rapid amplification of cDNA-end technology and named PnOLP1. A quantitative reverse transcription-PCR analysis showed that the signaling molecules methyl jasmonate, salicylic acid, ethylene, and hydrogen peroxide induced PnOLP1 expression to different degrees. In addition, the expression level of PnOLP1 rapidly increased within 48 h of inoculating P. notoginseng with the root rot pathogen Fusarium solani. Subcellular localization revealed that PnOLP1 localized to the cell wall. A prokaryotic expression vector containing PnOLP1 was constructed and transformed into Escherichia coli BL21 (DE3), and in vitro antifungal assays were performed using the purified recombinant PnOLP1 protein. The recombinant PnOLP1 protein had strong inhibitory effects on the mycelial growth of F. oxysporum, F. graminearum, and F. solani. A plant PnOLP1-overexpression vector was constructed and transfected into tobacco, and the resistance of T2 transgenic tobacco against F. solani was significantly enhanced compared with wild-type tobacco. Moreover, a PnOLP1 RNAi vector was constructed and transferred to the P. notoginseng leaves for transient expression, and the decrease of PnOLP1 expression level in P. notoginseng leaves increased the susceptibility to F. solani. Thus, PnOLP1 is an important disease resistance gene involved in the defense responses of P. notoginseng to F. solani.

Identification, characterization, and antifungal activity of cysteine peptidases from Calotropis procera latex

Cysteine peptidases (EC 3.4.22) are the most abundant enzymes in latex fluids. However, their physiological functions are still poorly understood, mainly related to defense against phytopathogens. The present study reports the cDNA cloning and sequencing of five undescribed cysteine peptidases from Calotropis procera (Aiton) Dryand (Apocynaceae) as well as some in silico analyses. Of these, three cysteine peptidases (CpCP1, CpCP2, and CpCP3) were purified. Their enzymatic kinetics were determined and they were assayed for their efficacy in inhibiting the hyphal growth of phytopathogenic fungi. The mechanism of action was investigated by fluorescence and atomic force microscopy as well as by induction of reactive oxygen species (ROS). The deduced amino acid sequences showed similar biochemical characteristics and high sequence homology with several other papain-like cysteine peptidases. Three-dimensional models showed two typical cysteine peptidase domains (L and R domains), forming a "V-shaped" active site containing the catalytic triad (Cys, His, and Asn). Proteolysis of CpCP1 was higher at pH 7.0, whereas for CpCP2 and CpCP3 it was higher at 7.5. All peptidases exhibited optimum activity at 35 °C and followed Michaelis-Menten kinetics. However, the major difference among them was that CpCP1 exhibited highest V_max, K_m, K_cat and catalytic efficiency. All peptidases were deleterious to the two fungi tested, with IC₅₀ of around 50 μg/mL. The peptidases promoted membrane permeabilization, morphological changes with leakage of cellular content, and induction of ROS in F. oxysporum spores. These results corroborate the hypothesis that latex cysteine peptidases play a role in defense against fungi.

Antifungal Proteins from Plant Latex

Latex, a milky fluid found in several plants, is widely used for many purposes, and its proteins have been investigated by researchers. Many studies have shown that latex produced by some plant species is a natural source of biologically active compounds, and many of the hydrolytic enzymes are related to health benefits. Research on the characterization and industrial and pharmaceutical utility of latex has progressed in recent years. Latex proteins are associated with plants' defense mechanisms, against attacks by fungi. In this respect, there are several biotechnological applications of antifungal proteins. Some findings reveal that antifungal proteins inhibit fungi by interrupting the synthesis of fungal cell walls or rupturing the membrane. Moreover, both phytopathogenic and clinical fungal strains are susceptible to latex proteins. The present review describes some important features of proteins isolated from plant latex which presented in vitro antifungal activities: protein classification, function, molecular weight, isoelectric point, as well as the fungal species that are inhibited by them. We also discuss their mechanisms of action.

Antifungal Activity of Arginine-Based Surfactants

Background:

Amino acid based surfactants constitute an important class of surface active biomolecules showing remarkable biocompatible properties. Antimicrobial activity is one of the most remarkable biological properties of this kind of surfactants, which have been widely studied against a broad spectrum of microorganisms. However, the antifungal activity of this kind of compound has been less well investigated. The aim of this work is the study of the antifungal activity of two novel argininebased surfactants (Nα-benzoyl-arginine decylamide, Bz-Arg-NHC10 and Nα-benzoyl-arginine dodecylamide, Bz-Arg-NHC12), obtained by an enzymatic strategy, against phytopathogenic filamentous fungi and dermatophyte strains.

Methods:

Four phytopathogenic fungi (Fusarium oxysporum, Fusarium solani, Colletotrichum gloeosporioides and Colletotrichum lindemuthianum) and two human pathogenic fungi (dermatophytes Trichophyton rubrum and Trichophyton mentagrophytes) were tested. Inhibition of vegetative growth and conidia germination was investigated for the phytopathogenic fungi. In order to elucidate the possible mechanism of biocide action, membrane integrity, as well as the production of reactive oxygen species (ROS) were evaluated. Additionally, the inhibition of germination of dermatophyte microconidia due to both arginine-based surfactants was studied. Minimum inhibitory concentration, as well as the concentration that inhibits 50% of germination were determined for both compounds and both fungal strains.

Results:

For the vegetative growth of phytopathogenic fungi, the most potent arginine-based compound was Bz-Arg-NHC10. All the tested compounds interfered with the conidia development of the studied species. Investigation of the possible mechanism of toxicity towards phytopathogenic fungi indicated direct damage of the plasma membrane and production of ROS. For the two strains of dermatophyte fungi tested, all the proved compounds showed similar fungistatic efficacy.

Conclusion:

: Bz-Arg-NHC10 and Bz-Arg-NHC12 were demonstrated to have broad biocidal ability against the proliferative vegetative form and the asexual reproductive conidia. Results suggest that both membrane permeabilization and induction of oxidative stress are part of the antifungal mechanisms involved in the interruption of normal conidia development by Bz-Arg-NHCn, leading to cell death.

Gene Cloning, Expression, and Antifungal Activities of Permatin from Naked Oat (Avena nuda)

Thaumatin-like proteins (TLPs) are the products of a large, highly complex gene family involved in host defense. TLPs also belong to the pathogenesis-related family 5 (PR-5) of plant defense proteins. Most TLPs exhibit potential antifungal activities, and their accumulation in the plant is related to many physiological processes. In this study, a gene encoding TLP named permatin with an open reading frame of 678 bp encoding a protein of 225 amino acids with a calculated molecular mass of 23.5 kDa was cloned from naked oat leaves. Phylogenetic analysis revealed that permatin shares high homology with a number of other TLPs among diverse taxa. Model of structure by homology modeling showed that permatin consists of an acidic cleft region consistent with most TLPs. Recombinant NusA-permatin was overexpressed in Escherichia coli strain BL21 and purified by Heparin column combined with Sephacryl S-200 column. The protein exhibited antifungal activity to Fusarium oxysporum (half maximal inhibitory concentration, IC₅₀ = 21.42 μM). Morphological observation showed that NusA-permatin can induce mycelium deformation of F. oxysporum, the cell membrane is blurred, and the diaphragm is not obvious. NusA-permatin also causes membrane permeabilization and reactive oxygen species accumulation in the mycelium of F. oxysporum. Permatin may play an important role in the disease resistance responses of plants against pathogen attacks through its antifungal activity.

Osmotin: A plant defense tool against biotic and abiotic stresses

Plants are prone to a number of pathogens and abiotic stresses that cause various disorders. However, plants possess a defense mechanism to cope with these stresses. The osmotin protein belongs to the PR-5 family of Pathogenesis-related (PR) proteins, which are produced in response to diseases caused by various biotic and abiotic stresses. Osmotin uses a signal transduction pathway to inhibit the activity of defensive cell wall barriers and increases its own cytotoxic efficiency. However, in response to cytotoxic effects, this pathway stimulates a mitogen-activated protein kinase (MAPK) cascade that triggers changes in the cell wall and enables osmotin's entrance into the plasma membrane. This mechanism involves cell wall binding and membrane perturbation, although the complete mechanism of osmotin activity has not been fully elucidated. Osmotin possesses an acidic cleft that is responsible for communication with its receptor in the plasma membrane of fungi. Osmotin is also involved in the initiation of apoptosis and programmed cell death, whereas its overexpression causes the accumulation of proline in transgenic plants. A higher concentration of osmotin can cause the lysis of hyphae tips. This review highlights the role of osmotin protein in the plant defense mechanism and its mode of action against numerous pathogens in wild and transgenic plants.

The osmotin of Calotropis procera latex is not expressed in laticifer-free cultivated callus and under salt stress

The latex of Calotropis procera has previously been reported to contain osmotin. This protein (CpOsm) inhibited phytopathogens and this was mechanistically characterized. Here, the time-course profile of CpOsm transcripts was examined in the salt-stressed cultivated callus of C. procera in order to better understand its role in the physiology of the plant. Stressed callus (80 mM NaCl) showed an unbalanced content of organic compounds (proline and total soluble sugar) and inorganic ions (Na⁺, Cl^-, and K⁺). Under salt treatment, the transcripts of CpOsm were detected after 12 h and slightly increased to a maximum at day seven, followed by reduction. Interestingly, CpOsm was not detected in the soluble protein fraction recovered from the salt-stressed callus as probed by electrophoresis, dot/Western blotting and mass spectrometry. The results suggested that (1) CpOsm is not constitutive in cultivated cells (laticifer-free tissues); (2) CpOsm transcripts appear under salt-stressed conditions; (3) the absence of CpOsm in the protein fractions of stressed cultivated cells indicated that salt-induced transcripts were not used for protein synthesis and this accounts to the belief that CpOsm may be a true laticifer protein in C. procera. More effort will be needed to unveil this process. In this study we show evidences that CpOsm gene is responsive to salt stress. However the corresponding protein is not produced in cultivated cells. Therefore, presently the hypothesis that CpOsm is involved in abiotic stress is not fully supported.

A novel peroxidase purified from Marsdenia megalantha latex inhibits phytopathogenic fungi mediated by cell membrane permeabilization

An antifungal class III peroxidase was purified from Marsdenia megalantha latex (named Mo-POX) using DEAE-cellulose and gel filtration chromatography on a Superose 12 HR 10/30 column. Mm-POX has an apparent molecular mass of 67.0kDa and a pI of 5.2, shares identity with other peroxidases, and follows Michaelis-Menten kinetics. It has a high affinity for guaiacol and hydrogen peroxide. The pH and temperature optima for Mm-POX were 5.0-7.0 and 60°C, respectively. The catalytic activity of Mm-POX was decreased in the presence of classic peroxidase inhibitors including azide, dithiothreitol, ethylenediamine tetraacetic acid, and sodium metabisulfite and high concentrations of Na⁺, Mn⁺, and salicylic acid. In contrast, Ca⁺ and Mg⁺, even at low concentrations, enhanced the Mm-POX enzymatic activity. This protein inhibited the germination of the conidia of the phytopathogenic fungi Fusarium oxysporum and Fusarium solani by acting through a membrane permeabilization mechanism. Mm-POX also induced oxidative stress in F. solani. Mm-POX is the first enzyme to be isolated from the M. megalantha species and it has potential use in the control of plant disease caused by important phytopathogenic fungi. This adds biotechnological value to this enzyme.

New findings in potential applications of tobacco osmotin

The osmotin protein is involved in both monocot and dicot plant responses to biotic and abiotic stress. To determine the biological activity of osmotin, the gene was amplified from tobacco genomic DNA, fused with the hexahistidine tag motif and successfully expressed in Escherichia coli, after which the recombinant osmotin was purified and renatured. Various activities were then tested, including hemolytic activity, toxicity against human embryonic kidney cells, and the antifungal activity of the recombinant osmotin. We found that osmotin had no adverse effects on human kidney cells up to a concentration of 500 μg.ml-1. However, the purified osmotin also had significant antimicrobial activity, specifically against fungal pathogens causing candidiasis and otitis, and against the common food pathogens. Using the osmotin-Agrobacterium construct, the osmotin gene was inserted into tobacco plants in order to facilitate the isolation of recombinant protein. Using qPCR, the presence and copy number of the transgene was detected in the tobacco plant DNA. The transgene was also quantified using mRNA, and results indicated a strong expression profile, however the native protein has been never isolated. Once the transgene presence was confirmed, the transgenic tobacco plants were grown in high saline concentrations and monitored for seed germination and chlorophyll content as indicators of overall plant health. Results indicated that the transgenic tobacco plants had a higher tolerance for osmotic stress. These results indicate that the osmotin gene has the potential to increase crop tolerance to stresses such as fungal attack and unfavorable osmotic conditions.

First insights into the diversity and functional properties of chitinases of the latex of Calotropis procera

Chitinases (EC 3.2.1.14) found in the latex of Calotropis procera (Ait) R. Br. were studied. The proteins were homogeneously obtained after two ion exchange chromatography steps. Most proteins were identified individually in 15 spots on 2-D gel electrophoresis with isoelectric points ranging from 4.6 to 6.0 and molecular masses extending from 27 to 30 kDa. Additionally, 66 kDa proteins were identified as chitinases in SDS-PAGE. Their identities were further confirmed by mass spectrometry (MS) analysis of the tryptic digests of each spot and MS analysis of the non-digested proteins. Positive reaction for Schiff's reagent suggested the proteins are glycosylated. The chitinases exhibited high catalytic activity toward to colloidal chitin at pH 5.0, and this activity underwent decay in the presence of increasing amounts of reducing agent dithiothreitol. Spore germination and hyphae growth of two phytopathogenic fungi were inhibited only marginally by the chitinases but were affected differently. This suggested a complex relationship might exist between the specificity of the proteins toward the fungal species. The chitinases showed potent insecticidal activity against the Bruchidae Callosobruchus maculatus, drastically reducing survival, larval weight and adult emergence. It is concluded that closely related chitinases are present in the latex of C. procera, and the first experimental evidence suggests these proteins are involved more efficiently in defence strategies against insects rather than fungi.

A thaumatin-like protein of Ocimum basilicum confers tolerance to fungal pathogen and abiotic stress in transgenic Arabidopsis

Plant often responds to fungal pathogens by expressing a group of proteins known as pathogenesis-related proteins (PRs). The expression of PR is mediated through pathogen-induced signal-transduction pathways that are fine-tuned by phytohormones such as methyl jasmonate (MeJA). Here, we report functional characterization of an Ocimum basilicum PR5 family member (ObTLP1) that was identified from a MeJA-responsive expression sequence tag collection. ObTLP1 encodes a 226 amino acid polypeptide that showed sequence and structural similarities with a sweet-tasting protein thaumatin of Thaumatococcus danielli and also with a stress-responsive protein osmotin of Nicotiana tabacum. The expression of ObTLP1 in O. basilicum was found to be organ-preferential under unstressed condition, and responsive to biotic and abiotic stresses, and multiple phytohormone elicitations. Bacterially-expressed recombinant ObTLP1 inhibited mycelial growth of the phytopathogenic fungi, Scleretonia sclerotiorum and Botrytis cinerea; thereby, suggesting its antifungal activity. Ectopic expression of ObTLP1 in Arabidopsis led to enhanced tolerance to S. sclerotiorum and B. cinerea infections, and also to dehydration and salt stress. Moreover, induced expression of the defense marker genes suggested up-regulation of the defense-response pathways in ObTLP1-expressing Arabidopsis upon fungal challenge. Thus, ObTLP1 might be useful for providing tolerance to the fungal pathogens and abiotic stresses in crops.

Cloning, characterization, and bacterial over-expression of an osmotin-like protein gene from Solanum nigrum L. with antifungal activity against three necrotrophic fungi

A new osmotin-like protein gene from Solanum nigrum L. var indica (SindOLP) was cloned and overexpressed in Escherichia coli. The full-length intron-less gene is 744 bp, encoding a mature protein of 247 amino acids with a molecular mass of 26 kDa. The protein has an N-terminal cleavable signal sequence of 21 amino acids. There is the Thaumatin family signature pattern, with one each of amidation, N-myristoylation, casein kinase II phosphorylation, tyrosine kinase phosphorylation, and protein kinase C phosphorylation sites. Hydropathy plot showed that it has six transmembrane helices. It has antifungal activity and can permeabilize fungal hyphae and spores. SindOLP is most active at pH 8, 25 °C and its antifungal activity is retained after 75 °C for 30 min. SindOLP inhibits fungal spore germination. The protein however lacks glucanase activity. The potential for SindOLP in developing fungus-resistant, transgenic crops is discussed.

Crystal structure of an antifungal osmotin-like protein from Calotropis procera and its effects on Fusarium solani spores, as revealed by atomic force microscopy: Insights into the mechanism of action

CpOsm is an antifungal osmotin/thaumatin-like protein purified from the latex of Calotropis procera. The protein is relatively thermostable and retains its antifungal activity over a wide pH range; therefore, it may be useful in the development of new antifungal drugs or transgenic crops with enhanced resistance to phytopathogenic fungi. To gain further insight into the mechanism of action of CpOsm, its three-dimensional structure was determined, and the effects of the protein on Fusarium solani spores were investigated by atomic force microscopy (AFM). The atomic structure of CpOsm was solved at a resolution of 1.61Å, and it contained 205 amino acid residues and 192 water molecules, with a final R-factor of 18.12% and an Rfree of 21.59%. The CpOsm structure belongs to the thaumatin superfamily fold and is characterized by three domains stabilized by eight disulfide bonds and a prominent charged cleft, which runs the length of the front side of the molecule. Similarly to other antifungal thaumatin-like proteins, the cleft of CpOsm is predominantly acidic. AFM images of F. solani spores treated with CpOsm resulted in striking morphological changes being induced by the protein. Spores treated with CpOsm were wrinkled, and the volume of these cells was reduced by approximately 80%. Treated cells were covered by a shell of CpOsm molecules, and the leakage of cytoplasmic content from these cells was also observed. Based on the structural features of CpOsm and the effects that the protein produces on F. solani spores, a possible mechanism of action is suggested and discussed.

New constitutive latex osmotin-like proteins lacking antifungal activity

Proteins that share similar primary sequences to the protein originally described in salt-stressed tobacco cells have been named osmotins. So far, only two osmotin-like proteins were purified and characterized of latex fluids. Osmotin from Carica papaya latex is an inducible protein lacking antifungal activity, whereas the Calotropis procera latex osmotin is a constitutive antifungal protein. To get additional insights into this subject, we investigated osmotins in latex fluids of five species. Two potential osmotin-like proteins in Cryptostegia grandiflora and Plumeria rubra latex were detected by immunological cross-reactivity with polyclonal antibodies produced against the C. procera latex osmotin (CpOsm) by ELISA, Dot Blot and Western Blot assays. Osmotin-like proteins were not detected in the latex of Thevetia peruviana, Himatanthus drasticus and healthy Carica papaya fruits. Later, the two new osmotin-like proteins were purified through immunoaffinity chromatography with anti-CpOsm immobilized antibodies. Worth noting the chromatographic efficiency allowed for the purification of the osmotin-like protein belonging to H. drasticus latex, which was not detectable by immunoassays. The identification of the purified proteins was confirmed after MS/MS analyses of their tryptic digests. It is concluded that the constitutive osmotin-like proteins reported here share structural similarities to CpOsm. However, unlike CpOsm, they did not exhibit antifungal activity against Fusarium solani and Colletotrichum gloeosporioides. These results suggest that osmotins of different latex sources may be involved in distinct physiological or defensive events.

Plant antifungal proteins and their applications in agriculture

Fungi are far more complex organisms than viruses or bacteria and can develop numerous diseases in plants that cause loss of a substantial portion of the crop every year. Plants have developed various mechanisms to defend themselves against these fungi which include the production of low-molecular-weight secondary metabolites and proteins and peptides with antifungal activity. In this review, families of plant antifungal proteins (AFPs) including defensins, lectins, and several others will be summarized. Moreover, the application of AFPs in agriculture will also be analyzed.

Glochidioboside Kills Pathogenic Bacteria by Membrane Perturbation

The aim of this study was to evaluate the antibacterial effects of glochidioboside and determine its mechanism of action. Glochidioboside has been reported to be isolated from some plants but the underlying biological properties have remained largely obscure until now. To identify the antibacterial activity of all biological properties, pathogenic bacteria susceptibility test was performed, and the result shows that the compound displays remarkable antibacterial activity against antibiotic-resistant bacteria not to mention general pathogen. To demonstrate membrane disruption and depolarization, SYTOX green and bis-(1,3-dibutylbarbituric acid) trimethine oxonol were used with Escherichia coli O157, and indicated that glochidioboside affected cytoplasmic membranes by permeabilization and depolarization, respectively. Calcein efflux was evident in a membrane model that encapsulated fluorescent dye, and supported the hypothesis of a membrane-active mechanism. To confirm the release of intracellular matrix owing to membrane damage, the movements of potassium ion were observed; the results indicated that the cells treated with glochidioboside leaked potassium ion, thus the damage induced by the compounds lead to leaking intracellular components. We propose that glochidioboside kills pathogenic bacteria via perturbation of integrity of the membrane.

Osmotin: a plant sentinel and a possible agonist of mammalian adiponectin

Osmotin is a stress responsive antifungal protein belonging to the pathogenesis-related (PR)-5 family that confers tolerance to both biotic and abiotic stresses in plants. Protective efforts of osmotin in plants range from high temperature to cold and salt to drought. It lyses the plasma membrane of the pathogens. It is widely distributed in fruits and vegetables. It is a differentially expressed and developmentally regulated protein that protects the cells from osmotic stress and invading pathogens as well, by structural or metabolic alterations. During stress conditions, osmotin helps in the accumulation of the osmolyte proline, which quenches reactive oxygen species and free radicals. Osmotin expression results in the accumulation of storage reserves and increases the shelf-life of fruits. It binds to a seven-transmembrane-domain receptor-like protein and induces programmed cell death in Saccharomyces cerevisiae through RAS2/cAMP signaling pathway. Adiponectin, produced in adipose tissues of mammals, is an insulin-sensitizing hormone. Strangely, osmotin acts like the mammalian hormone adiponectin in various in vitro and in vivo models. Adiponectin and osmotin, the two receptor binding proteins do not share sequence similarity at the amino acid level, but interestingly they have a similar structural and functional properties. In experimental mice, adiponectin inhibits endothelial cell proliferation and migration, primary tumor growth, and reduces atherosclerosis. This retrospective work examines the vital role of osmotin in plant defense and as a potential targeted therapeutic drug for humans.

New insights into the structure and mode of action of Mo-CBP3, an antifungal chitin-binding protein of Moringa oleifera seeds

Mo-CBP3 is a chitin-binding protein purified from Moringa oleifera Lam. seeds that displays inhibitory activity against phytopathogenic fungi. This study investigated the structural properties and the antifungal mode of action of this protein. To this end, circular dichroism spectroscopy, antifungal assays, measurements of the production of reactive oxygen species and microscopic analyses were utilized. Mo-CBP3 is composed of 30.3% α-helices, 16.3% β-sheets, 22.3% turns and 30.4% unordered forms. The Mo-CBP3 structure is highly stable and retains its antifungal activity regardless of temperature and pH. Fusarium solani was used as a model organism for studying the mechanisms by which this protein acts as an antifungal agent. Mo-CBP3 significantly inhibited spore germination and mycelial growth at 0.05 mg.mL-1. Mo-CBP3 has both fungistatic and fungicidal effects, depending on the concentration used. Binding of Mo-CBP3 to the fungal cell surface is achieved, at least in part, via electrostatic interactions, as salt was able to reduce its inhibitory effect. Mo-CBP3 induced the production of ROS and caused disorganization of both the cytoplasm and the plasma membrane in F. solani cells. Based on its high stability and specific toxicity, with broad-spectrum efficacy against important phytopathogenic fungi at low inhibitory concentrations but not to human cells, Mo-CBP3 has great potential for the development of new antifungal drugs or transgenic crops with enhanced resistance to phytopathogens.

Crystallization and X-ray diffraction analysis of an antifungal laticifer protein

An osmotin (CpOsm) from the latex of Calotropis procera has been crystallized in both tetragonal and trigonal forms suitable for structure determination. Crystallographic studies of CpOsm are of great interest because limited information is available concerning the structure of latex proteins and CpOsm has previously been shown to interact with the spore membranes of some plant pathogenic fungi, thus impairing spore germination and hyphal growth. CpOsm crystals were grown using 0.1 M HEPES buffer pH 7.5, 26% PEG 4000, 0.2 M ammonium sulfate (space group P4(3)) or using 0.1 M HEPES buffer pH 7.5, 35% MPD, 0.7 M ammonium sulfate (space group P3(1)12). X-ray diffraction data were collected to 2.17 Å (P4(3)) and 1.80 Å (P3(1)12) resolution and molecular-replacement analyses produced initial phases for both crystal forms.

The grapevine expression atlas reveals a deep transcriptome shift driving the entire plant into a maturation program

We developed a genome-wide transcriptomic atlas of grapevine (Vitis vinifera) based on 54 samples representing green and woody tissues and organs at different developmental stages as well as specialized tissues such as pollen and senescent leaves. Together, these samples expressed ∼91% of the predicted grapevine genes. Pollen and senescent leaves had unique transcriptomes reflecting their specialized functions and physiological status. However, microarray and RNA-seq analysis grouped all the other samples into two major classes based on maturity rather than organ identity, namely, the vegetative/green and mature/woody categories. This division represents a fundamental transcriptomic reprogramming during the maturation process and was highlighted by three statistical approaches identifying the transcriptional relationships among samples (correlation analysis), putative biomarkers (O2PLS-DA approach), and sets of strongly and consistently expressed genes that define groups (topics) of similar samples (biclustering analysis). Gene coexpression analysis indicated that the mature/woody developmental program results from the reiterative coactivation of pathways that are largely inactive in vegetative/green tissues, often involving the coregulation of clusters of neighboring genes and global regulation based on codon preference. This global transcriptomic reprogramming during maturation has not been observed in herbaceous annual species and may be a defining characteristic of perennial woody plants.

Pilot Study with regard to the Wound Healing Activity of Protein from Calotropis procera (Ait.) R. Br

We provide the scientific basis for the use of Calotropis procera for treating skin and wound infections in traditional medicine. The aqueous extract of stem-bark of C. procera exhibited more pronounced potent antimicrobial activity. Calo-protein was purified and identified from the most-active aqueous extracts of C. procera and showed broad-spectrum activity. Calo-protein inhibited the growth of S. aureus and E. aerogenes effectively at 25 μg/ml concentration. Mice topically treated with Calo-protein revealed significant wound healing after 14 days comparable to fusidic acid (FA) as positive control. This protein was devoid of cytolytic effect even at higher concentrations on skin cells after 24 h. Further investigation of this Calo-protein of C. procera on bacterial inhibition may provide a better understanding of the scientific basis and justification for its use in traditional medicine.

Anticonvulsant action of Calotropis procera latex proteins

Calotropis procera (Ait.) R.Br. is a laticiferous plant belonging to the Apocynaceae family. C. procera latex proteins were evaluated with respect to anticonvulsant and sedative activity in mouse models of pentylenetetrazol (PTZ)-, pilocarpine-, and strychnine-induced convulsions or turning behavior and pentobarbital-induced sleep. In the strychnine- and pilocarpine-induced seizure models, C. procera latex proteins caused no significant alterations in latencies to convulsions and death, as compared with controls. In the PTZ-induced seizure model, administration of C. procera latex proteins in high doses (50 or 100mg/kg) and diazepam caused significant increases in latencies to convulsions and death. C. procera latex proteins (50 or 100mg/kg) and 2mg/kg diazepam caused a decrease in sleep latency and an increase in sleep time compared with the control group and groups treated with 5 or 10mg/kg. Our results suggest that C. procera latex proteins have a central nervous system-depressant activity as reflected in their potentiation of pentobarbital-induced sleeping time and their anticonvulsant action in the PTZ-induced seizure model.