Figure 1. The evolution of chloroplasts by endosymbiosis. The primary chloroplasts arose through the capture and retention of a cyanobacterium by a phagotrophic eukaryote. Subsequent gene loss and transfer to the nucleus (arrowed) resulted in the evolution of the chloroplast organelle. This organelle spread to other eukaryotes by secondary endosymbiotic events in which eukaryotic algae were themselves engulfed. In two phyla the endosymbiont nucleus remains as a vestigial structure, the nucleomorph.

Figure 2. Biolistic transformation of the chloroplast. The genetic engineering of the chloroplast genome can be achieved using the biolistic process in which DNA is delivered into the organelle compartment using a particle gun. The DNA is coated onto gold microparticles that are fired at the target cells or tissue. Recombination results in the integration of the DNA into the genome. The bottom panel illustrates the disruption of a chloroplast gene using a selectable marker conferring spectinomycin (Spc) resistance (Rochaix, 1997).

Figure 3. Protein targeting into the chloroplast. In primary plastids, proteins synthesized in the cytosol are transported across the outer and inner membranes by a translocon complex (blue) that recognizes the transit peptide. This peptide is then removed by a stromal peptidase. In complex plastids, an additional peptide signal directs the protein across the outermost membrane as it is being translated on membrane-bound ribosomes. This signal peptide is cleaved by a signal peptidase. How proteins cross the inner membrane of the CER is not known.