Interdisciplinary Graduate Programs Symposium
2014 OSU Molecular Life Sciences
Interdisciplinary Graduate Programs Symposium
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Poster abstracts
Abstract:
Transposable elements (TEs) are mobile, parasitic DNA elements found throughout all life. When active, they cause mutations and destabilize chromosomes. These alterations can damage the germline and cause or accelerate disease, and in many eukaryotes, TEs and remnant sequences make up large portions of the genome. Eukaryotes have developed several homologous small RNA (sRNA) and epigenetic systems to control the expression and transposition of TEs. However, little is known about initial TE recognition by the host.
How does an organism differentiate self from non-self sequence in the nuclear genome? This is relevant for the silencing of TEs, transgenes, and viruses. Our lab has found that newly introduced copies of endogenous TEs are recognized by homology to existing copies, mediated by sRNAs.1 Other labs have transformed active Nicotiana tabacum retrotransposons into Arabidopsis thaliana.2,3 Despite a lack of homology to the host genome, these elements were not only recognized, but heritably silenced after introduction and transposition. However, there is little evidence for how this silencing was triggered or what pathways may be involved.
Using Agrobacterium-mediated transformation, we have introduced one of these TEs, Tto14, into Arabidopsis. Analysis of DNA methylation and sRNA has shown that Tto1 is quickly and deeply silenced in this first generation. This is dependent on the RNA-directed DNA Methylation pathway and is independent of the RNA interference pathway (RNAi). From sRNA northern blot, we infer that this TE is being recognized through its homology to endogenous TEs, in spite of its limited sequence similarity to any region of the Arabidopsis genome. However, when homology based recognition is eliminated, RNAi is active against the element instead. Using truncated forms of this TE, we have also seen that full silencing requires the entire element. In order to minimize homology, further studies will examine the recognition of yeast TEs.
References:
1. Nuthikattu, S., McCue, A. D., Panda, K., Fultz, D., DeFraia, C., Thomas, E. N., & Slotkin, R. K (2013). The Initiation of Epigenetic Silencing of Active Transposable Elements Is Triggered by RDR6 and 21-22 Nucleotide Small Interfering RNAs. PLANT PHYSIOLOGY.
2. Hirochika, H., Okamoto, H., & Kakutani, T (2000). Silencing of Retrotransposons in Arabidopsis and Reactivation by the ddm1 Mutation. The Plant Cell Online.
3.Pérez-Hormaeche, J., Potet, F., Beauclair, L., & Lucas, H (2008). Invasion of the Arabidopsis genome by the tobacco retrotransposon Tnt1 is controlled by reversible transcriptional gene silencing. Plant Physiology.
4.Böhmdorfer, G., Tramontano, A., Luxa, K., & Bachmair, A (2010). A synthetic biology approach allows inducible retrotransposition in whole plants. Systems And Synthetic Biology.
Keywords: Transposon, Epigenetics, Silencing
