The revolution in genetics and molecular biology that occurred towards the end of the twentieth century inspired enormous progress in understanding many aspects of the molecular control of development of different organisms. It has also aided our understanding of how information contained in their respective genomes gives rise to large populations of different proteins, termed the proteome. In turn, these proteins interact with metabolites enabling the organism to develop its specific phenotype. Moreover, the use of molecular genetic techniques enabled genetic systems to be altered artificially in order to exploit aspects of molecular synthesis or developmental biology for improvement of agricultural species of plants and animals.

Early on in this revolution, plastids were seen as an attractive system in which plant biotechnology could be performed, since they have several properties that are advantageous in this area. Also, as we have seen throughout this book, plastids carry out many vital processes in plant cells, which have the potential to be manipulated for improvement or increased efficiency, leading to crop plants with more optimised phenotypes for specific environments. Because plastids are organelles, which define a distinct compartment within the plant cell, sequestering novel molecules into the plastid compartment presents a major advantage compared with allowing accumulation of novel molecules in the cytosol where they could be toxic. Since the relative proportion of the plastid compartment size compared to the cytoplasmic volume is fairly high, the plastid represents a significant compartment in which novel molecules can be accumulated.