Deletions within a defective suppressor-mutator element in maize affect the frequency and developmental timing of its excision from the bronze locus.

Abstract

Six independent derivatives of the bz-m13 allele, which contains a 2.2-kilobase-pair defective Suppressor-mutator (dSpm) insertion at the bronze (bz) locus, were isolated and analyzed. The derivatives were selected for alterations in the frequency and timing of somatic reversion; such derivatives were analyzed genetically and designated changes in state. All of the derivatives analyzed revert substantially later in development than the original insertion mutation and some show a very low frequency of reversion as well. All of the derivates contain insertions at the same site as the parent bz-m13. Deletions of 400-1300 base pairs were found in the dSpm elements in 4 of the 6 derivatives; the remaining derivatives could not be distinguished structurally from the original mutant allele. Changes in the frequency and developmental timing of excision are attributable to alterations in the dSpm element. DNA sequences near the ends of the element are important for responding to the 2 trans-acting functions supplied by the transposition-competent Suppressor-mutator (Spm) element.