Chloroplast Biotechnology in Higher Plants: Expressing Antimicrobial Genes in the Plastid Genome

While genetic improvement of susceptible crop species may enhance resistance to microbial pathogens and facilitate reduced pesticide load, the possibility for transmission of novel genes to wild relatives has hampered acceptance of GM crops in some markets. Chloroplast transformation presents an attractive alternative to nuclear transformation and offers the potential to ameliorate these environmental concerns. Most agronomically important species exhibit maternal inheritance of organellar genomes which eliminates the threat of transgene escape through pollen. Gene silencing is absent due to site directed, single copy insertion by homologous recombination. Foreign proteins can accumulate to high levels (up to 50% of total soluble protein) and are retained within the chloroplast envelope protecting them from degradation by host cytoplasmic proteases. A bacterial chloroperoxidase gene (cpo-p) was transformed into the tobacco chloroplast genome to test its efficacy against plant pathogens and the mycotoxin producing saprophyte Aspergillus flavus.