Purpose: This study provided a proof of concept that engineered plants expressing antimicrobial agent can reduce the microbial load in leafy plants.
Methods: The synthetic codon-optimized genes encoding an antimicrobial peptide, lactoferricin, were introduced into the model plant, Arabidopsis thaliana through Agrobacterium-mediated gene transformation. The integration of the transgenes into the plant genome was confirmed by PCR; mRNA transcripts of the transgenes were detected in the leaves of the transgenic plants by reverse transcriptase PCR assays. The antimicrobial activity of transgenic Arabidopsis was evaluated by in vitro and in planta infiltration assays. In addition, a food-grade antimicrobial protein, lactoferrin, was transiently expressed in Romaine lettuce through vacuum-infiltration with Agrobacterium tumefaciens carrying vectors that encodes human lactoferrin.
Results: Total protein extract from two transgenic Arabidopsis lines that expressed lactoferricin reduced the Escherichia coli population (inoculum, 6.5 logs) by 86% and 78%, respectively, in the in vitro activity tests. Compared to the wildtype plants, three independent transgenic Arabidopsis lines expressing lactoferricin significantly decreased the infiltrated bacterial population (inoculum level, 4.5 logs) in leaves by 63%. The transient expression level of lactoferrin in lettuce was 57.8 ng/g lettuce tissue as determined by ELISA.
Significance: This is the first report of transgenic Arabidopsis with increased resistance to a foodborne human pathogen. The study suggested that transgenic technology is promising to promote the microbiological safety of fresh produce. Transgenic lettuce plants expressing antimicrobial agents for enhancing food safety are being developed in our group.