Methods to Isolate and Identify New Plant Signaling Peptides

Evaluation of the antimicrobial effects of Capsicum, Nigella sativa, Musa paradisiaca L., and Citrus limetta: A review

The extensive use of antibiotics and vaccines against microbial infections can result in long-term negative effects on humans and the environment. However, there are a number of plants that have antimicrobial effects against various disease-causing microbes such as bacteria, viruses, and fungi without negative side effects or harm to the environment. In this regard, four particular plants- Capsicum, Nigella sativa, Musa paradisiaca L., and Citrus limetta have been widely considered due to their excellent antimicrobial effect and ample availability. In this review, we discuss their antimicrobial effects due to the presence of thymoquinone, p-cymene, pinene, alkaloids, limonene, camphene, and melanin. These antimicrobial compounds disrupt the cell membrane of microbes, inhibit cellular division, and form biofilm in bacterial species, eventually reducing the number of microbes. Extraction of these compounds from the respective plants is carried out by different methods such as soxhlet, hydro-distillation, liquid-liquid extraction (LLE), pressurized liquid extraction (PLE), solid-phase extraction (SPE), supercritical fluid extraction (SFE), pulsed electric field (PEF), microwave-assisted extraction (MAE), enzyme-assisted extraction (EAE), ultrasound-assisted extraction (UAE), and high-voltage electrical discharge. Suitable selection of the extraction technique highly depends upon the associated advantages and disadvantages. In order to aid future study in this field, this review paper summarizes the advantages and disadvantages of each of these approaches. Additionally, the discussion covers how antimicrobial agents destroy harmful bacteria. Thus, this review offers in-depth knowledge to researchers on the antibacterial properties of Capsicum, Nigella sativa, Musa paradisiaca L. peels, and Citrus limetta.

Mining the genome of Arabidopsis thaliana as a basis for the identification of novel bioactive peptides involved in oxidative stress tolerance

Although evidence has accumulated on the role of plant peptides in the response to external conditions, the number of peptide-encoding genes in the genome is still underestimated. Using tiling arrays, we identified 176 unannotated transcriptionally active regions (TARs) in Arabidopsis thaliana that were induced upon oxidative stress generated by the herbicide paraquat (PQ). These 176 TARs could be translated into 575 putative oxidative stress-induced peptides (OSIPs). A high-throughput functional assay was used in the eukaryotic model organism Saccharomyces cerevisiae allowing us to test for bioactive peptides that increase oxidative stress tolerance. In this way, we identified three OSIPs that, upon overexpression in yeast, resulted in a significant rise in tolerance to hydrogen peroxide (H2O2). For one of these peptides, the decapeptide OSIP108, exogenous application to H2O2-treated yeast also resulted in significantly increased survival. OSIP108 is contained within a pseudogene and is induced in A. thaliana leaves by both the reactive oxygen species-inducer PQ and the necrotrophic fungal pathogen Botrytis cinerea. Moreover, infiltration and overexpression of OSIP108 in A. thaliana leaves resulted in increased tolerance to treatment with PQ. In conclusion, the identification and characterization of OSIP108 confirms the validity of our high-throughput approach, based on tiling array analysis in A. thaliana and functional screening in yeast, to identify bioactive peptides.