University of Oregon

Mutator and Spm elements at the B-Peru locus --Linda J. Harris, Garth I. Patterson, and Vicki L. Chandler The B-Peru allele regulates anthocyanin synthesis in both kernel and plant tissues. We have used a stock of Robertson's Mutator to isolate four unstable and four stable (upon self-pollination) mutations in B-Peru (Chandler et al., MNL 62:56). Genetic and Southern blot analyses demonstrate that all eight mutants are the result of insertions within an ~5 kb region of the B-Peru gene. A map of the B-Peru gene and the insertion sites are shown below.


All eight insertions alter pigment synthesis in all kernel and plant tissues pigmented by B-Peru, suggesting that each insertion has disrupted a region of the gene required for expression in all tissues.

Two insertion alleles have been cloned using B sequences. b-Perum5 contains an Spm-related element. Restriction mapping of the clone and genetic experiments suggest that it is an Spm-w element. Southern analysis of the b-Perum220 allele suggested that there had been a complex rearrangement at the B-Peru locus, including a duplication of B-Peru sequences. The cloning of a portion of the b-Perum220 allele revealed that a Mu1.7 element had inserted upstream of the B-Peru coding region.

Genetic analysis of one other unstable allele, b-Perum216, is consistent with the presence of a dSpm element in the B-Peru gene. None of the four unstable alleles contained Ac activity. Genetic and molecular analysis of the remaining five insertion alleles is underway.

These results demonstrate that both Mutator and Spm elements were active in our stocks. Crosses examining the progenitors of these stocks showed that Spm activity (identified by crosses to wx-m8, a dSpm) was present in the original Mutator stocks obtained from D. Robertson. No Spm activity was detected in our B-Peru and b r-g stocks. These results, combined with the low spontaneous mutation frequency observed in the progenitor B-Peru stock (less than 5 X 10-6) (MNL 62:56), suggest that the source of the Spm activity was the Mutator stocks. Thus, when using Mutator in transposon tagging experiments, we recommend monitoring the mutagenesis stocks and isolated mutants for the activity of other transposable element families.

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