A UC Davis group recently did a plastid-based phylogenetic reconstruction of the relatives of Pistachio . Plastids may prove to be good targets for transformation. This protoxin was produced in very high levels, and when fed to target lepidopterans proved to be very effective. The plastid has mostly prokaryotic characteristics. If you're using a bacterial gene, the plastid genome is likely to be a better home than the nucleus.
Plastids are multicopy organelles, and their genomes are present in multiple copies per plastid.
High levels of expression are likely to be expected. Rhodes discovered CMS when working with maize accessions from Peru. The stock he discovered was later lost. As commercial plant breeding companies developed around the use of hybrid seed, other sources of CMS were discovered. When backcrossed into a normal maize inbred, each of these cytoplasms result in male sterility.