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Regulation of Transposable Element Activities during Plant Development

We have studied the regulation of the maize Ac and MuDR transposable elements activities during plant development. Ac was studied in an heterologous system (transgenic tobacco plants and cell suspensions) while MuDR was studied in the native maize background. The focus of this study was on the transcriptional regulation of Ac and MuDR. For Ac, the major achievements were to show that 1-It is autoregulated in a way that the Ac-encoded transposase can repress the activity of its own promoter; 2-It is expressed at low basal level in all the plant organs that were studied, and its activity is stronger in dividing tissues -- a behaviour reminiscent of housekeeping genes; 3- the activity of Ac promoter is cell cycle regulated -- induced at early S-phase and increasing until mitosis; 4- host factor binding sites were identified at both extremities of Ac and may be important for transposition. For MuDR, It was shown that it encodes two genes, mudrA and mudrB, convergently transcribed from near-identical promoters in the terminal inverted repeats. Distinct 5' start sites, alternative splicing, production of antisense RNA and tissue specificity were all shown to be involved in the regulation of MuDR.