Abstract
Plastid transformation technology has several potential advantages for basic researches and biotechnological applications, including high-level gene expression and gene containment. Glutamine synthetase activity in chloroplasts is responsible for scavenging ammonia produced in the photorespiratory pathway. Indeed, nuclear transformants overexpressing plastidic GS2 showed an improved tolerance to high-intensity light (Kozaki and Takeba, 1996). The nuclear transformants had twice the normal amount of GS2. To achieve higher levels of GS2 protein accumulation in chloroplasts, we have over-expressed rice GS2 gene in chloroplasts. The chloroplast transformants accumulated 40-fold GS2 proteins compared to non-transformed plants in leaves. Plastid-expressed GS2 could provide very high levels (5-7-fold) GS2 activity. Gel chromatography and non-denaturing PAGE analyses demonstrated the formation of catalytically active octamer of GS2 in the transplatomic plants overexpressing GS2.
