Transformation of an edible crop with the pagA gene of Bacillus anthracis.

Vaccination against anthrax is the most important strategy to combat the disease. This study describes a generation of edible transgenic crop expressing, functional protective antigen (PA). In vitro studies showed that the plant-expressed antigen is qualitatively similar to recombinant PA. Immunization studies in mouse animal models indicated the generation of PA-specific neutralizing antibodies and stressed the need for improving expression levels to generate higher antibody titers. Genetic engineering of a plant organelle offers immense scope for increasing levels of antigen expression. An AT-rich PA gene (pagA) coding for the 83-kDa PA molecule was thus cloned and expressed in tobacco chloroplasts. Biolistics was used for the transformation of a chloroplast genome under a set of optimized conditions. The expression of the pagA gene with 69% AT content was highly favored by an AT-rich chloroplast genome. A multifold expression level of functional PA was obtained as compared with the nuclear transgenic tobacco plants. This report describes for the first time a comprehensive study on generating transgenic plants expressing PA, which may serve as a source of an edible vaccine against anthrax. Two important achievements of expressing PA in an edible crop and use of chloroplast technology to enhance the expression levels are discussed here.