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Plant Cell Advance Online Publication
Published on November 11, 2005; 10.1105/tpc.105.036350

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Received July 19, 2005
Returned for revision September 26, 2005
Accepted October 12, 2005

Localization of the Tomato Bushy Stunt Virus Replication Protein p33 Reveals a Peroxisome-to-Endoplasmic Reticulum Sorting Pathway

Andrew W. McCartney 1, John S. Greenwood 1, Marc R. Fabian 2, K. Andrew White 2, and Robert T. Mullen 1*

1 Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
2 Department of Biology, York University, Toronto, Ontario M3J 1P3, Canada

* To whom correspondence should be addressed. E-mail: rtmullen{at}uoguelph.ca.

Tomato bushy stunt virus (TBSV), a positive-strand RNA virus, causes extensive inward vesiculations of the peroxisomal boundary membrane and formation of peroxisomal multivesicular bodies (pMVBs). Although pMVBs are known to contain protein components of the viral membrane-bound RNA replication complex, the mechanisms of protein targeting to peroxisomal membranes and participation in pMVB biogenesis are not well understood. We show that the TBSV 33-kD replication protein (p33), expressed on its own, targets initially from the cytosol to peroxisomes, causing their progressive aggregation and eventually the formation of peroxisomal ghosts. These altered peroxisomes are distinct from pMVBs; they lack internal vesicles and are surrounded by novel cytosolic vesicles that contain p33 and appear to be derived from evaginations of the peroxisomal boundary membrane. Concomitant with these changes in peroxisomes, p33 and resident peroxisomal membrane proteins are relocalized to the peroxisomal endoplasmic reticulum (pER) subdomain. This sorting of p33 is disrupted by the coexpression of a dominant-negative mutant of ADP-ribosylation factor1, implicating coatomer in vesicle formation at peroxisomes. Mutational analysis of p33 revealed that its intracellular sorting is also mediated by several targeting signals, including three peroxisomal targeting elements that function cooperatively, plus a pER targeting signal resembling an Arg-based motif responsible for vesicle-mediated retrieval of escaped ER membrane proteins from the Golgi. These results provide insight into virus-induced intracellular rearrangements and reveal a peroxisome-to-pER sorting pathway, raising new mechanistic questions regarding the biogenesis of peroxisomes in plants.






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