Studies into the regulation and expression of Z. mays Ac in heterologous plant species

The Z. mays Ac/Ds transposable elements have been introduced into a number of heterologous plant species, where they have been employed as genomic mutagens in transposon-tagging strategies. Although successful, many strategies fail to regulate the expression of the controlling Ac element, therefore allowing Ds transposition to occur throughout the plant life cycle. This can generate genetically mosaic organisms whose progeny may contain unique or common Ds transposition events. In an attempt to develop a controlled Ac/Ds transposon-tagging strategy, this thesis examined whether an anther-specific APG-Ac element could limit Ds transposition events exclusively to the post-meiotic microspore, thus providing a somatically stable, inheritable system of Ds transposition in which each pollen grain would harbour a unique Ds transposition event. The experiments presented in this thesis conclude that APG-Ac does limit Ds transposition to pollen development within N. tabacum, and individual progeny derived from pollen harbouring a transposition event does contain a Ds element reinserted into a unique location in the genome.;Although this work demonstrates the potential for a gametophytic Ac/Ds transposon-tagging strategy, parallel experiments in A. thaliana suggested that the APG-Ac element does not function as anticipated in this species. Whilst assaying the expression of APG-Ac in A. thaliana, it became apparent that the Ac transposase transcript was incorrectly processed. Subsequent experiments clearly demonstrate that A. thaliana alternatively splices and prematurely polyadenylates TPase transcript, such that the correctly processed mRNA constitutes only a small proportion of the total Ac message. In an attempt to remedy this problem, a modified Ac gene was designed and cloned which lacks Ac sequence possibly responsible for the incorrect mRNA processing. It is hoped that further work will show whether the modified APG-Ac element can generate in A. thaliana the gametophytic Ds transposition evident in N. tabacum.;.