Tag1 is an autonomous element in Arabidopsis thaliana that is a member of the Ac (or hAT) superfamily of elements that duplicates 8 bp of genomic sequence upon insertion. The pattern of Tag1 excision shows that the timing of excision is restricted in shoot development producing independent germinal revertants and very small somatic sectors in leaves, sepals, and siliques, behavior similar to that of Mutator in maize. In some cases, Tag1 somatic excision shows a burst of activity during the mid to late stages of leaf expansion that follows a wave from the leaf tip/edges to the petiole, similar to what has been described for sink to source transitions that occur in leaves. Transcription of Tag1 produces a major 2.3 kb transcript that encodes a putative transposase with nuclear localization sequences and whose abundance increases dramatically following Agrobacterium-mediate transformation with Tag1 sequences. The long term goal of this research is to elaborate the mechanisms and identify the host genes that control the timing of Tag1 excision. The present aims are to (I) determine how the timing and pattern of Tag1 excision activity during leaf expansion correlate with sink to source transitions in Arabidopsis and how environmental and genetic factors affect Tag1 excision behavior, (II) identify mutations in both Tag1 and the Arabidopsis genome that alter the timing and pattern of excision, (III) identify the sequences within Tag1 that activate transcription of endogenous Tag1 elements following transformation and (IV) identify transposase components and transposase binding sites required for Tag1 excision.
Transposable elements provide powerful tools for studying genetic and molecular mechanisms that control development. Their transposition produce sectors that follow the cell lineages of the host and generate new mutations in the host's genome. These properties have been exploited for mutagenesis, gene shuttling, gene isolation and cell lineage studies. Analysis of the frequency and timing of transposition have revealed transcriptional and post-transcriptional mechanisms (including methylation, alternative splicing and promoter activation) that control when and where transposition occurs. These studies will advance our knowledge of the developmental and genetic control of transposition in plants, improve the usefulness of Tag1 as a tool for genome analysis and contribute to our understanding of how genomes evolve and how developmental processes are regulated.
