Transgenic plastids in basic research and plant biotechnology

Facile methods of genetic transformation are of outstanding importance for both basic and applied research. For many years, transgenic technologies for plants were restricted to manipulations of the nuclear genome. More recently, a second genome of the plant cell has become amenable to genetic engineering: the prokaryotically organized circular genome of the chloroplast. The possibility to directly manipulate chloroplast genome-encoded information has paved the way to detailed in vivo studies of virtually all aspects of plastid gene expression. Moreover, plastid transformation technologies have been intensely used in functional genomics by performing gene knockouts and site-directed mutageneses of plastid genes. These studies have contributed greatly to our understanding of the physiology and biochemistry of biogenergetic processes inside the plastid compartment. Plastid transformation technologies have also stirred considerable excitement among plant biotechnologists, since transgene expression from the plastid genome offers a number of most attractive advantages, including high-level foreign protein expression and transgene containment due to lack of pollen transmission. This review describes the generation of plants with transgenic plastids, summarizes our current understanding of the transformation process and highlights selected applications of transplastomic technologies in basic and applied research.