Antimicrobial peptides are widely found in living organisms and are known to play a critical role in innate immunity. Numerous antimicrobial peptides from diverse species appear to be effective against pathogenic microorganisms of bacteria, fungi, protozoa, and viruses. Because antibiotic resistance is a global health issue in the fight against pathogenic microorganisms, there has been an urgent need for development of new antibiotic substances. In the current study, we performed yeast two hybrid screening using Beclin1 bait in order to find new peptide antibiotics from a random peptide library. Two candidate peptides from the screening were expressed in a yeast secretory system of Pichia pastoris and tested for any antimicrobial activity against Staphylococcus aureus, MRSA, MRSA2242, MRSA2250, Lactobacillus casei, and Lactobacillus acidophilus. Disc clear zone assay and spectrophotometric analysis revealed that the two peptides exert a decent activity against the pathogenic bacteria, in contrast to minimal effect on the commensal Lactobacillus strains. Taken together, this study presents novel peptides with antibacterial activity against the pathogenic forms of Staphylococcus aureus and suggests the possibility that these peptides, upon further characterization, may be developed as clinically useful antibiotics.

Cucumber mosaic virus (CMV), which has the broadest host range among plant viruses, is a very destructive pathogen in pepper production. Various resistance sources against CMV have been identified by plant breeders. One of them is Capsicum annuum ‘Bukang’, which contains a single dominant resistance gene, Cmr1. C. annuum ‘Bukang’ is resistant to CMV-P0 strains (CMV-Kor and CMV-Fny), but susceptible to CMV-P1. CMV-P1 is a new strain recently identified in South Korea. Previously we showed that CMV-P1 RNA1 helicase domain is responsible for overcoming Cmr1 and may be play a role in viral replication and systemic infection. To identify the plant host factors involved in CMV-P1 replication and movement, we utilized a yeast two-hybrid system derived from C. annuum ‘Bukang’ cDNA library as a prey. A total of 78 potential host genes interacting with the CMV-P1 RNA1 helicase domain were isolated in the first screening, and PCR confirmation and sequencing analysis narrowed the candidates to ten genes. The candidate genes have found to be encoding acireductone dioxygenase, ADP-glucose pyrophosphorylase, ADP-ribosylation factor 1, ADP-ribosylation factor, calreticulin-3 precursor, cysteine synthase, formate dehydrogenase, histone-H3, phosphomannomutase and polyubiqutin 6PU11. Previous studies showed that these genes were involved in virus infection, replication or virus movement. To elucidate the function of these genes, VIGS and coimmumo precipitation assay is being done.