EMS Mutagenesis and Point Mutation Discovery

One of the ultimate goals of biotechnology is to design beneficial phenotypes and then achieve them by altering gene expression. For any given organism that is a target of biotechnological improvement, an indexed collection of every single base change that created either a non-silent missense mutation or a truncated gene product would be ideal. Such a collection would provide the most flexibility in design of new varieties. While the number of mutant lines for such an idealized scenario is prohibitive, lines with a high density of point mutations can provide the starting material for a similar sort of approach.

The two greatest sources of point mutations are spontaneous mutation and chemical mutagenesis. Both of these sources rely on altering bases in DNA and then allowing the DNA replication system to use the altered base as a template, creating the mutation. In maize, where mutagenesis of pollen is quite straightforward (Neuffer 1994), this has been the method of choice for several decades, primarily because it avoids the creation of chimaeric plants that may or may not transmit induced mutations to progeny. To avoid lysis of the pollen by aqueous solutions, an emulsion of the mutagen is made in paraffin oil, and the pollen mixed in.