Since the first demonstration of stable transgene integration in the plastid genome (plastome) of higher plants, plastid transformation has been used for a wide range of purposes, including basic studies as well as biotechnological applications, showing that transplastomic plants are an effective system to produce recombinant proteins. Compared to nuclear transformation, the main advantages of this technology are the high and stable production level of proteins as well as the natural containment of transgenes. To date, more than 100 transgenes have been successfully expressed in plant chloroplasts. In some cases, however, unintended pleiotropic effects on plant growth and physiology were shown in transplastomic plants. In this paper, we review such effects and discuss some of the technologies developed to overcome them.
