Whither transgenics?

Before we get into a primer about plant metabolism and the things that are and are not easy to do with plants and their genomes, lets get conceptual about some common GM crops.

Most people have heard of Bt corn, there is also Bt cotton, soybeans, potatoes etc. Bt stands for Bacillus thuringiensis, a   microbe whose spores and preparations have been used to control parasite infestations in crops since the 1920s. In its ideal state, Bt-plants have been modified so that every cell of the plant produces one or more cry proteins, which pierce holes in the midgut of many insects, killing them. This protein is fairly directly expressed from a gene in B. thuringiensis, so as long as the plant genome has those cry genes and it doesn't cause toxicity to the plant, those plants will be toxic to pests.

The first commercial Bt-plants were tobacco plants grown back in 1985. This modification is a fairly simple expression of the central dogma of biology: DNA->RNA ->protein. As long as the central dogma holds true, this modification should work.

Toxin expression is fairly boring to the hobbyist, however, and although you could produce other valuable proteins, like insulin or human growth hormone, non-central dogma concerns make this pretty much non-viable. Plant proteins, post-translation, are modified differently than human ones, and we aren't going to go into the difficult and not clinically tested methods for "humanizing" plants.