| In course of McClintock's study on radiation induced chromosome breakage, she observed frequent chromosome break generated at a specific locus on chromosome 9. The precision of frequent breaks at this particular locus led to the discovery of Ac/Ds elements. In recent years, molecular characterization of Ac/Ds induced chromosome breaks reveal that when multiple transposon ends are in proximity, the transposase could recognize non-canonical transposon ends resulting in various kinds of chromosomal rearrangements including deletion, inversion, translocation, duplication and, sometimes, chromosome breaks. Previous studies in our lab show that in the maize P1-rr11 allele of the P1 gene, a 5'end and a 3'end of Ds element are in reversed orientation with reference to each other. Transposition involving these two ends resulted in deletions and inversions in the flanking DNA.;In this thesis we present our study on the efficacy of a synthetic reversed-ends Ds element, modeled after the configuration found in P1-rr11 , to cause deletions and inversions in Arabidopsis genome. Our study revealed that the reversed-ends Ds element is efficient in generating both deletions and inversions in the genome. The sizes of the rearrangements range from 2kb to several megabases. Analysis of the DNA sequences at the transposon insertion sites suggests that transposition at the reversed-ends element could be linear (participating TIRs on same chromatid) or non-linear (participating TIRs on sister chromatids).;Ac/Ds insertion in maize is characterized by 8bp duplication at the target site. In contrast, we find that insertion of the reversed-ends Ds element is flush or it is associated with 8bp or 1bp target site duplication. In some of the transposition events, the sequences at the rearrangement junctions suggest that the excised transposon-ends formed a hairpin between the two strands.;The significant contributions of our study are: It validates the utility of the reversed-ends Ds element as a genomics tool to cause chromosomal rearrangements.;It addresses certain fundamental questions such as the size of target site duplication upon Ds insertion and, formation of hairpin structure at the transposon ends. These observations highlight possible difference in the transposition mechanism of Ds element in maize and Arabidopsis. |
