University of Cambridge > > Plant Sciences Departmental Seminars > Cajal bodies, the nucleolus and fibrillarin are required for a plant virus systemic infection

Cajal bodies, the nucleolus and fibrillarin are required for a plant virus systemic infection

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The nucleolus and Cajal bodies are prominent interacting subnuclear domains involved in crucial aspects of cell function such as RNA metabolism, the cell cycle and aging. Certain viruses interact with these compartments but the functions of such interactions are largely uncharacterized. We have recently shown that the ability of the Groundnut rosette virus ORF3 protein to move viral RNA long-distances through the phloem, the specialized vascular system used by plants for the transport of assimilates and macromolecules, strictly depends on its interaction with Cajal bodies, the nucleolus and the major nucleolar protein, fibrillarin. The ORF3 protein targets and re-organizes Cajal bodies into multiple Cajal body-like structures and then enters the nucleolus by causing fusion of these structures with the nucleolus. This process is mediated by the interaction between ORF3 protein and fibrillarin leading to the formation of ring-like complexes. Using atomic force microscopy we have determined the architecture of these complexes as single-layered ring-like structures with a diameter of 18-22 nm and height of 1.9-2.5 nm which consist of equal number (6-8) of ORF3 protein and fibrillarin molecules. A model of structural organization of fibrillarin-ORF3 protein complexes will be presented. It is suggested that ORF3 protein and fibrillarin can move from the nucleus to the cytoplasm in a form of these ring-like complexes. Furthermore, in the cytoplasm, these rings formed by both ORF3 and fibrillarin proteins interact with viral RNA encapsidating it and re-organizing it into helical structures, and thereby play a key role in the assembly of umbraviral RNP complexes capable of long-distance movement and systemic infection. These results demonstrate novel functions for fibrillarin as an essential component of translocatable viral RNPs and may have functional implications for other plant viruses and development of new approaches to control virus defence responses which will be discussed.

This talk is part of the Plant Sciences Departmental Seminars series.

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