The N-glycosidase activity of the ribosome-inactivating protein ME1 targets single-stranded regions of nucleic acids independent of sequence or structural motifs

Structural Distinctive 26SK, a Ribosome-Inactivating Protein from Jatropha curcas and Its Biological Activities

Ribosome-inactivating proteins (RIPs) are a group of proteins exhibiting N-glycosidase activity leading to an inactivation of protein synthesis. Thirteen predicted Jatropha curcas RIP sequences could be grouped into RIP types 1 or 2. The expression of the RIP genes was detected in seed kernels, seed coats, and leaves. The full-length cDNA of two RIP genes (26SK and 34.7(A)SK) were cloned and studied. The 34.7(A)SK protein was successfully expressed in the host cells while it was difficult to produce even only a small amount of the 26SK protein. Therefore, the crude proteins were used from E. coli expressing 26SK and 34.7(A)SK constructs and they showed RIP activity. Only the cell lysate from 26SK could inhibit the growth of E. coli. In addition, the crude protein extracted from 26SK expressing cells displayed the effect on the growth of MDA-MB-231, a human breast cancer cell line. Based on in silico analysis, all 13 J. curcas RIPs contained RNA and ribosomal P2 stalk protein binding sites; however, the C-terminal region of the P2 stalk binding site was lacking in the 26SK structure. In addition, an amphipathic distribution between positive and negative potential was observed only in the 26SK protein, similar to that found in the anti-microbial peptide. These findings suggested that this 26SK protein structure might have contributed to its toxicity, suggesting potential uses against pathogenic bacteria in the future.

The role of enzymatic activities of antiviral proteins from plants for action against plant pathogens

Antiviral proteins (AVPs) from plants possess multiple activities, such as N-glycosidase, RNase, DNase enzymatic activity, and induce pathogenesis-related proteins, salicylic acid, superoxide dismutase, peroxidase, and catalase. The N-glycosidase activity releases the adenine residues from sarcin/ricin (S/R) loop of large subunit of ribosomes and interfere the host protein synthesis process and this activity has been attributed for antiviral activity in plant. It has been shown that AVP binds directly to viral genome-linked protein of plant viruses and interfere with protein synthesis of virus. AVPs also possess the RNase and DNase like activity and may be targeting nucleic acid of viruses directly. Recently, the antifungal, antibacterial, and antiinsect properties of AVPs have also been demonstrated. Gene encoding for AVPs has been used for the development of transgenic resistant crops to a broad range of plant pathogens and insect pests. However, the cytotoxicity has been observed in transgenic crops using AVP gene in some cases which can be a limiting factor for its application in agriculture. In this review, we have reviewed various aspects of AVPs particularly their characteristics, possible mode of action and application.

Opuntin B, the antiviral protein isolated from prickly pear (Opuntia ficus-indica (L.) Miller) cladode exhibits ribonuclease activity

An antiviral protein, designated Opuntin B, was purified from Prickly Pear (Opuntia ficus-indica (L.) Miller) Cladode by heat treatment of the extract, protein precipitation by ammonium sulfate treatment followed by ion-exchange chromatography. Assessment of enzymatic activity of the purified protein showed that it degrades total plant genomic RNA, while causing electrophoretic mobility shifting of Cucumber mosaic virus (CMV) RNAs. However, heat-denatured viral RNA became sensitive to degradation upon treatment with antiviral protein. Opuntin B had no DNase activity on native and heat-denatured apricot genomic DNA, and on PCR-amplified coat protein gene of CMV. Using CMV as prey protein and Opuntin B as bait protein, no interaction was found between the antiviral protein and viral coat protein in far western dot blot analysis.

Integration of transcriptomics, proteomics and metabolomics data to reveal the biological mechanisms of abrin injury in human lung epithelial cells

BACKGROUND

Abrin toxin (AT) is a potent plant toxin that belongs to the type Ⅱ ribosome inactivating protein family and is recognized as an important toxin agent for potential bioweapons. Exposure to AT by way of aerosol is the most lethal route, but the mechanism of injury requires further investigation.

MATERIALS AND METHODS

In the present study, we performed a comprehensive analysis of transcriptomics, proteomics and metabolomics on the potential mechanism of abrin injury in human lung epithelial cells.

RESULTS

In total, 6838 genes, 314 proteins and 178 metabolites showed significant changes in human lung epithelial cells after AT treatment. Using molecular function, pathway, and network analysis, the genes and proteins regulated in AT-treated cells were mainly attributed to amino acid metabolism, lipid metabolism, and genetic information processing. Furthermore, a comprehensive analysis of the transcripts, proteins, and metabolites was performed. The results revealed that the correlated genes, proteins, and metabolism pathways regulated in AT-treated human lung epithelial cells were involved in tryptophan metabolism, biosynthesis of amino acids, and protein digestion and absorption.

CONCLUSION

This study provides large-scale omics data to develop new strategies for the prevention, rapid diagnosis, and treatment of AT poisoning, especially AT from aerosol.

Digestion of chrysanthemum stunt viroid by leaf extracts of Capsicum chinense indicates strong RNA-digesting activity

KEY MESSAGE

CSVd could not infect Nicotiana benthamiana when the plants were pretreated with crude leaf extract of Capsicum chinense 'Sy-2'. C. chinense leaves were revealed to contain strong RNA-digesting activity. Several studies have identified active antiviral and antiviroid agents in plants. Capsicum plants are known to contain antiviral agents, but the mechanism of their activity has not been determined. We aimed to elucidate the mechanism of Capsicum extract's antiviroid activity. Chrysanthemum stunt viroid (CSVd) was inoculated into Nicotiana benthamiana plants before or after treating the plants with a leaf extract of Capsicum chinense 'Sy-2'. CSVd infection was determined using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) 3 weeks after inoculation. When Capsicum extract was sprayed or painted onto N. benthamiana before inoculation, it was effective in preventing infection by CSVd. To evaluate CSVd digestion activity in leaf extracts, CSVd was mixed with leaf extracts of Mirabilis, Phytolacca, Pelargonium and Capsicum. CSVd-digesting activities were examined by quantifying undigested CSVd using qRT-PCR, and RNA gel blotting permitted visualization of the digested CSVd. Only Capsicum leaf extract digested CSVd, and in the Capsicum treatment, small digested CSVd products were detected by RNA gel blot analysis. When the digesting experiment was performed for various cultivars and species of Capsicum, only cultivars of C. chinense showed strong CSVd-digesting activity. Our observations indicated that Capsicum extract contains strong RNA-digesting activity, leading to the conclusion that this activity is the main mechanism for protection from infection by CSVd through spraying or painting before inoculation. To our knowledge, this is the first report of a strong RNA-digesting activity by a plant extract.

Plant toxin abrin induced oxidative stress mediated neurodegenerative changes in mice

Abrin is a potent plant toxin. It is a heterodimeric protein toxin which is obtained from the seeds of Abrus precatorius plant. At cellular level abrin causes protein synthesis inhibition by removing the specific adenine residue (A4324) from the 28s rRNA of the 60S - ribosomal subunit. In the present study we investigated the role of oxidative stress in neurotoxic potential and demyelinating effects of abrin on brain. The mechanism by which abrin induces oxidative damage and toxicity in brain are relatively unknown. Animals were exposed to 0.4 and 1.0 LD50 abrin dose by intraperitoneal route and observed for 1 and 3 day post-toxin exposure. Oxidative stress occurred in brain due to abrin was confirmed in terms of increased reactive oxygen species (ROS), glutathione depletion and increased lipid peroxidation. Significant increase in blood and brain ROS was observed at day 3, 1 LD50. Abrin induced changes in the neurotransmitters (5-hydroxy tryptamine, norepinephrine, dopamine and monoamine oxidase) levels were evaluated by spectroflourometry. Increase in the levels of 5-HT and NE was observed after abrin exposure. MAO activity was found to be decreased in abrin exposed animals compared to control. Significant inhibition in the activity of acetylcholine esterase enzyme in brain and serum was reported for both the doses and time points. Western blot analysis of iNOS expression indicated that abrin treatment resulted in dose and time dependent increase. Furthermore, protein expression of myelin basic protein (MBP) was down regulated in a dose and time dependent manner. Brain histopathology was carried out and cortical brain region showed demyelination after abrin exposure. Results confirmed that abrin poisoning leads to neurodegeneration and neurotoxicity mediated through oxidative stress, AChE inhibition, lipid peroxidation and decrease in MBP levels.

Protein synthesis inhibition activity by strawberry tissue protein extracts during plant life cycle and under biotic and abiotic stresses

Ribosome-inactivating proteins (RIPs), enzymes that are widely distributed in the plant kingdom, inhibit protein synthesis by depurinating rRNA and many other polynucleotidic substrates. Although RIPs show antiviral, antifungal, and insecticidal activities, their biological and physiological roles are not completely understood. Additionally, it has been described that RIP expression is augmented under stressful conditions. In this study, we evaluated protein synthesis inhibition activity in partially purified basic proteins (hereafter referred to as RIP activity) from tissue extracts of Fragaria × ananassa (strawberry) cultivars with low (Dora) and high (Record) tolerance to root pathogens and fructification stress. Association between the presence of RIP activity and the crop management (organic or integrated soil), growth stage (quiescence, flowering, and fructification), and exogenous stress (drought) were investigated. RIP activity was found in every tissue tested (roots, rhizomes, leaves, buds, flowers, and fruits) and under each tested condition. However, significant differences in RIP distribution were observed depending on the soil and growth stage, and an increase in RIP activity was found in the leaves of drought-stressed plants. These results suggest that RIP expression and activity could represent a response mechanism against biotic and abiotic stresses and could be a useful tool in selecting stress-resistant strawberry genotypes.

Biological control of wood decay against fungal infection

Wood (timber) is an important raw material for various purposes, and having biological composition it is susceptible to deterioration by various agents. The history of wood protection by impregnation with synthetic chemicals is almost two hundred years old. However, the ever-increasing public concern and the new environmental regulations on the use of chemicals have created the need for the development and the use of alternative methods for wood protection. Biological wood protection by antagonistic microbes alone or in combination with (bio)chemicals, is one of the most promising ways for the environmentally sound wood protection. The most effective biocontrol antagonists belong to genera Trichoderma, Gliocladium, Bacillus, Pseudomonas and Streptomyces. They compete for an ecological niche by consuming available nutrients as well as by secreting a spectrum of biochemicals effective against various fungal pathogens. The biochemicals include cell wall-degrading enzymes, siderophores, chelating iron and a wide variety of volatile and non-volatile antibiotics. In this review, the nature and the function of the antagonistic microbes in wood protection are discussed.

The biology of viroid-host interactions

Viroids are single-stranded, circular, and noncoding RNAs that infect plants. They replicate in the nucleus or chloroplast and then traffic cell-to-cell through plasmodesmata and long distance through the phloem to establish systemic infection. They also cause diseases in certain hosts. All functions are mediated directly by the viroid RNA genome or genome-derived RNAs. I summarize recent advances in the understanding of viroid structures and cellular factors enabling these functions, emphasizing conceptual developments, major knowledge gaps, and future directions. Newly emerging experimental systems and research tools are discussed that are expected to enable significant progress in a number of key areas. I highlight examples of groundbreaking contributions of viroid research to the development of new biological principles and offer perspectives on using viroid models to continue advancing some frontiers of life science.

Nicking activity on pBR322 DNA of ribosome inactivating proteins from Phytolacca dioica L. leaves

Ribosome-inactivating proteins isolated from Phytolacca dioica L. leaves are rRNA-N-glycosidases, as well as adenine polynucleotide glycosylases. Here we report that some of them cleave supercoiled pBR322 dsDNA, generating relaxed and linear molecules. PD-L1, the glycosylated major form isolated from the winter leaves of adult P . dioica plants, produces both free 3'-OH and 5'-P termini randomly distributed along the DNA molecule, as suggested by labelling experiments with [alpha- 32P]dCTP and [gamma- 32 P]dATP. Moreover, when the reaction is carried out under low-salt conditions, cleavage is observed mainly at a specific site, located downstream of the ampicillin resistance gene (close to position 3200), ending with the deletion of a fragment of approximately 70 nucleotides. This cleavage pattern is similar to that obtained under the same conditions with mung bean nuclease, a single-strand endonuclease. Furthermore, pBR322 DNA treated with PD-L1 shows reduced transforming activity with E . coli HB101 competent cells in comparison to untreated control plasmid DNA.

Inducible Expression of a Phytolacca heterotepala Ribosome-Inactivating Protein Leads to Enhanced Resistance Against Major Fungal Pathogens in Tobacco

ABSTRACT Plant genetic engineering has long been considered a valuable tool to fight fungal pathogens because it would limit the economically costly and environmentally undesirable chemical methods of disease control. Ribosome-inactivating proteins (RIPs) are potentially useful for plant defense considering their antiviral and antimicrobial activities but their use is limited by their cytotoxic activity. A new gene coding for an RIP isolated from leaves of Phytolacca heterotepala was expressed in tobacco under the control of the wound-inducible promoter of the bean polygalacturonase-inhibiting protein I gene to increase resistance against different fungal pathogens, because an individual RIP isolated from P. heterotepala showed direct antifungal toxicity. Phenotypically normal transgenic lines infected with Alternaria alternata and Botrytis cinerea showed a significant reduction of leaf damage while reverse transcription-polymerase chain reaction and western analysis indicated the expression of the RIP transgene upon wounding and pathogen attack. This work demonstrates that use of a wound-inducible promoter is useful to limit the accumulation of antimicrobial phytotoxic proteins only in infected areas and that the controlled expression of the PhRIP I gene can be very effective to control fungal pathogens with different phytopathogenic actions.

Viroids and viroid-host interactions

Although they induce symptoms in plants similar to those accompanying virus infections, viroids have unique structural, functional, and evolutionary characteristics. They are composed of a small, nonprotein-coding, single-stranded, circular RNA, with autonomous replication. Viroid species are clustered into the families Pospiviroidae and Avsunviroidae, whose members replicate (and accumulate) in the nucleus and chloroplast, respectively. Viroids replicate in three steps through an RNA-based rolling-circle mechanism: synthesis of longer-than-unit strands catalyzed by host RNA polymerases; processing to unit-length, which in the family Avsunviroidae is mediated by hammerhead ribozymes; and circularization. Within the initially infected cells, viroid RNA must move to its replication organelle, with the resulting progeny then invading adjacent cells through plasmodesmata and reaching distal parts via the vasculature. To carry out these movements, viroids must interact with host factors. The mature viroid RNA could be the primary pathogenic effector or, alternatively, viroids could exert their pathogenic effects via RNA silencing.