Production of enzymes in transgenic maize kernels: Maize seed is an excellent system in which to produce proteins for industrial applications. Seed provides a stable environment for the protein—over millennia the seed has evolved mechanisms to stably store proteins for later use by the germinating embryo. The growing, harvesting and processing of maize seed is established in the US. Maize is a commodity crop and as such, the total processing costs can be kept to a minimum, allowing inexpensive recovery of various fractions of the grain. One of the major advantages of using the embryo (germ) instead of the endosperm to produce industrial proteins, particularly cellulases, is that the endosperm starch can be separated from the embryo and converted into ethanol. Thus, if the major use of the crop is for ethanol anyway, the production of the germ is a by-product, making the enzyme in the germ virtually free. The oil can be used in food/feed or biodiesel applications, creating another co-product. High levels of recombinant protein accumulation in maize germ are routine. Although other plant systems for example tobacco, offer advantages such as being a non-food plant, issues including growing, harvesting, processing and non-seed-based expression create production problems.
