Two Maize Genes Are Each Targeted Predominantly by Distinct Classes of Mu Elements

The Mutator transposable element system of maize has been used to isolate mutations at many different genes. Six different classes of Mu transposable elements have been identified. An important question is whether particular classes of Mu elements insert into different genes at equivalent frequencies. To begin to address this question, we used a small number of closely related Mutator plants to generate multiple independent mutations at two different genes. The overall mutation frequency was similar for the two genes. We then determined what types of Mu elements inserted into the genes. We found that each of the genes was preferentially targeted by a different class of Mu element, even when the two genes were mutated in the same plant. Possible explanations for these findings are discussed. These results have important implications for cloning Mu-tagged genes as other genes may also be resistant or susceptible to the insertion of particular classes of Mu elements.