An investigation of insertion specificity and genetic background effects in the Mutator transposable element system of maize

April Diane Cresse, Purdue University

Abstract

The Robertson's Mutator system of maize is a recently described transposable element system which induces mutations at an exceptionally high frequency. The Mu1 transposable elements of this system are responsible for the majority of Mutator-induced mutations. The insertion site of Mu1-like elements was analysed to determine the extent of insertion specificity in this system. The sequence and copy number of the DNA flanking Mu elements isolated from active Mutator plants was determined. Sequence analyses revealed perfect nine base target duplications flanking the insert in thirteen of fourteen cases. The results indicated that Mu1-like elements are primarily found in regions of the maize genome that are of low copy number. This preferential selection of low copy number, gene-like DNA as targets for Mu element insertion was not directed by any specific primary sequences that could be detected in this study. A second set of experiments was performed in an attempt to identify specific genetic background effects on the Mutator system. Many different maize lines were crossed to active Mutator plants. The activity of a somatically unstable allele at the Bronze1 locus (BzMum4) was followed through several generations of recurrent outcrossing to standard maize lines. No extreme genetic background effects were detected. The single most important factor which determined whether Mutator somatic activity would be maintained in subsequent generations was found to be the Mutator parent plant. Mutator activity was retained for five and six generations in two different inbred maize lines as determined by somatic mutability at the Bronze1 locus, indicating that inbreeding does not, per se, severely inhibit Mutator activity.

Degree

Ph.D.

Advisors

Bennetzen, Purdue University.

Subject Area

Genetics|Molecular biology

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