Transposable elements are the main component of higher genomes. The LTR retro-transposons replicate via RNA intermediates, and resemble to retroviruses in both structure and life cycle. The active ones encode the Gag protein, which packages the elements int o Virus-Like Particles (VLPs, assembled from multiple Gag units), and the Pol poly-protein, which allows reverse transcription and integration. The LARDs are non-autonomous LTR retro-transposons, and do not encode these proteins. They are able to transpose, probably by parasitizing active partners, as do defective interfering particles on retroviruses in animal cells. This project aims to study the mechanism of such hyper-parasitic elements, using the LARD within the large Triticeae genome as a model. The fir st objective is to find the autonomous partners, using four integrated approaches. Bioinformatics and PCR analyses will inform about the potential partners for the reverse transcription, and cellular biology and one-hybrid methods about the potential partn ers for the packaging. The second objective is a functional genomics analysis of the dynamic interactions of LARDs with their active partners, by identifying the keys sequences for the packaging and LARD inhibitive activity regarding their active partners. The final objective is a survey on the abundance and the sequence evolution of the key domains of the LARDs and of their active partners, to shed light the evolution way of the LARD, their generalist vs. specific parasitic activity and the co-evolution of such genomic host-parasite interactions. Fundamental questions on parasitic behaviour in the genome, on host-parasite interactions as on the mechanism of trans-complementation of non-autonomous retro-elements will be addressed. Generic applications include the generation of new molecular markers, new transformation vectors and improvement of transgenic integration, and use of the negative interfering particles as a vaccinating system against retroviruses.
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