Engineering Plastid Pathways: An Environment-Friendly Alternative for in Planta Transformation

Abstract

The chloroplast, site of photosynthesis in higher plants and algae, fixes atmospheric CO2 to sugar and thus occupies a central position as the primary source of food. Every living organisms are directly or indirectly associated for their food requirements and thus survival to these green “plants.” Plastids of higher plants are semiautonomous and they represent cellular fraction of the cell, transmitted maternally during reproduction. Chloroplast genome is circular, self-replicating, multicopy number, highly polyploid, and has its own transcription–translation machinery. Chloroplast genome, plastome, represents 10–20% of total cellular genome despite of small size and codes for as many 130 genes. Due to their circular genome nature, plastome offers a homely environment to “incoming” transgene embedded in a circular vehicle, provides more chances of site-specific integration through homologous recombination. Transgene restraint due to lack of pollen transmission and maternal inheritance offers a great advantage over facile methods of plant genetic transformation through nuclear genome. Furthermore, high level of 288transgene expression and lack of gene silencing are an added advantage of plastid transformation. The study of chloroplast genome transformation leads to understanding of biochemistry and physiology of plastid metabolism. This article summarizes plastome organization and regeneration, the transformation process, and highlights selected applications of transplastomic technologies in basic and applied research.