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First published online November 21, 2008; 10.1104/pp.108.131755 Plant Physiology 149:1005-1016 (2009) © 2009 American Society of Plant Biologists OPEN ACCESS ARTICLE
The Cauliflower Mosaic Virus Protein P6 Forms Motile Inclusions That Traffic along Actin Microfilaments and Stabilize Microtubules1,[W],[OA]Plant Biology Division, Samuel Roberts Noble Foundation, Ardmore, Oklahoma 73401 (P.A.H., K.P., R.S.N.); and Department of Plant Microbiology and Pathology, University of Missouri, Columbia, Missouri 65211 (K.P., W.Y., J.E.S.)
The gene VI product (P6) of Cauliflower mosaic virus (CaMV) is a multifunctional protein known to be a major component of cytoplasmic inclusion bodies formed during CaMV infection. Although these inclusions are known to contain virions and are thought to be sites of translation from the CaMV 35S polycistronic RNA intermediate, the precise role of these bodies in the CaMV infection cycle remains unclear. Here, we examine the functionality and intracellular location of a fusion between P6 and GFP (P6-GFP). We initially show that the ability of P6-GFP to transactivate translation is comparable to unmodified P6. Consequently, our work has direct application for the large body of literature in which P6 has been expressed ectopically and its functions characterized. We subsequently found that P6-GFP forms highly motile cytoplasmic inclusion bodies and revealed through fluorescence colocalization studies that these P6-GFP bodies associate with the actin/endoplasmic reticulum network as well as microtubules. We demonstrate that while P6-GFP inclusions traffic along microfilaments, those associated with microtubules appear stationary. Additionally, inhibitor studies reveal that the intracellular movement of P6-GFP inclusions is sensitive to the actin inhibitor, latrunculin B, which also inhibits the formation of local lesions by CaMV in Nicotiana edwardsonii leaves. The motility of P6 along microfilaments represents an entirely new property for this protein, and these results imply a role for P6 in intracellular and cell-to-cell movement of CaMV.
1 This work was supported in part by the Samuel Roberts Noble Foundation (P.A.H., K.P., R.S.N.), by a National Science Foundation Multi-User Instrumentation Program award (grant no. DBI–0400580 to R.S.N.), by the U.S. Department of Agriculture National Research Initiative (grant no. USDA CSREES 98–35303–611 to J.E.S.), and by the Food for the 21st Century Program at the University of Missouri (J.E.S.). 2 Present address: Plant Biology Division, Samuel Roberts Noble Foundation, Inc., Ardmore, OK 73401. 3 Present address: Department of Biology, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong. 4 These authors contributed equally to the article. The authors responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) are: James E. Schoelz (schoelzj{at}missouri.edu) for CaMV-associated constructs and Richard S. Nelson (rsnelson{at}noble.org) for cytoskeleton gene constructs. [W] The online version of this article contains Web-only data. [OA] Open access articles can be viewed online without a subscription. www.plantphysiol.org/cgi/doi/10.1104/pp.108.131755 * Corresponding author; e-mail rsnelson{at}noble.org. Received October 27, 2008; accepted November 19, 2008; published November 21, 2008. Related articles in Plant Physiol.:
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