what do you mean by plastid transformation? give an example?

Chloroplasts are a class of plastids - organelles in plant cells ? apparently derived from a cyanobacteria (blue-green bacteria) ancestor that once lived symbiotically inside the plant cell. Chloroplasts contain chlorophyll and are found in the shoots and leaves of green plants, while colourless plastids are found in the roots and other coloured plastids are found in fruit. The number of plastids in each cell is variable, and each plastid contains multiple copies of its own genome, typically 50 to 100. Many plastid genomes have been sequenced. They resemble bacterial genomes in many respects; though features normally found in muticellular organisms, such as interrupted genes and RNA editing are also present. The chloroplast genome codes for the transcription and translation machinery of the chloroplast plus numerous structural proteins. But the vast majority of the chloroplast proteins are encoded in the plant nucleus and imported into the chloroplast after synthesis.

Stable transformation of the chloroplast ? putting foreign genes into the chloroplast genome - was first achieved in the single cell green alga Chlamydomonas reinhardtii in 1988, soon to be followed by tobacco plant, and more recently, Arabidopsis thaliano [1]. Several biotech companies, including Monsanto, Rhone-Poulenc, Novartis, American Cyanamid, Calgene, Pioneer Hybrid have initiated major programmes on chloroplast transformation since the late 1990s [2].

Chloroplast transformation has been touted at least as far back as 1998 as a means of  ?containing? transgenes; that is, preventing them from transferring to non-GM crops or wild relatives through pollen, and hence preventing the creation of transgenic herbicide tolerant weeds. The theory is that chloroplasts are inherited exclusively through the female line.