RNA silencing refers to the suppression of gene expression through nucleotide sequence-specific interactions that are mediated by 21-25nt-long RNA molecules, referred to as short interfering (si)RNAs. This process serves fundamental biological functions, including antiviral defence, developmental patterning and maintenance of genome integrity.
In plants and in some animals, the effects of post-transcriptional RNA silencing can extend beyond its sites of initiation, owing to the movement of signal molecules. Although the mechanisms and channels involved are different, plant and animal silencing signals must have RNA components that account for the nucleotide sequence-specificity of their effects.
A genetic screen carried out in the host laboratory has led to the identification of three silencing movement deficient (smd1,2,3) mutants of Arabidopsis that sustain cell-autonomous silencing but fail to display plamodesmal movement of silencing from vascular to mesophyll cells. In a first part of the project, the cell-cell and long-distance movement of viruses, proteins and phloem-transported dyes will be studied in smd backgrounds to determine if the mutations affect macromolecular trafficking and plasmodesmata aperture.
Biolistically-triggered RNA silencing will al so be employed to analyse the effect of smd mutations is manifested in non-vascular cells. In parallel, positional cloning of smd3 will be initiated, using an available mapping population. In the second part, we will investigate the impact, on silencing movement, of known mutations affecting RNA silencing components and host factors required for macromolecule and virus movement.
The third aspect will be focus on the recently identified trans-acting (ta)siRNAs in Arabidopsis. Could tasiRNAs act as non cell-autonomous regulators of endogenous gene expression? This project will significantly contribute to our understanding of the mechanisms and pathways that account for intercellular communications in plants.
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