High Stability of Recombinant Proteins Expressed in Tobacco Chloroplasts

Abstract

The green fluorescent protein and the non-toxic subunit of cholera toxin were expressed in tobacco chloroplasts. Both recombinant proteins accumulated to levels greater than 20% of the total soluble protein. We did not observe light-dependent induction of gene expression despite employing the promoter and 5´-UTR from the psbA gene. Both proteins were stable in young and old leaves. The estimated half-life, determined by pulse-chase labeling, was greater than 48 h. Freeze-drying of pulverized leaves supplied an easy method of post-harvest handling with no significant loss of the recombinant protein after 7 months of storage at room temperature. These data suggest that both proteins are good candidates for the expression of fusion proteins (e.g. with antigens) in tobacco chloroplasts.