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Journal of Virology, October 2006, p. 10096-10108, Vol. 80, No. 20
0022-538X/06/$08.00+0     doi:10.1128/JVI.01186-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Packaging of Brome Mosaic Virus Subgenomic RNA Is Functionally Coupled to Replication-Dependent Transcription and Translation of Coat Protein

Padmanaban Annamalai and A. L. N. Rao*

Department of Plant Pathology, University of California, Riverside, California 92521-0122

Received 7 June 2006/ Accepted 26 July 2006

In Brome mosaic virus (BMV), genomic RNA1 (gB1) and RNA2 (gB2), encoding the replication factors, are packaged into two separate virions, whereas genomic RNA3 (gB3) and its subgenomic coat protein (CP) mRNA (sgB4) are copackaged into a third virion. In vitro assembly assays performed between a series of deletion variants of sgB4 and wild-type (wt) CP subunits demonstrated that packaging of sgB4 is independent of sequences encoding the CP open reading frame. To confirm these observations in vivo and to unravel the mechanism of sgB4 copackaging, an Agrobacterium-mediated transient in vivo expression system (P. Annamalai and A. L. N. Rao, Virology 338:96-111, 2005) that effectively uncouples replication from packaging was used. Cultures of agrotransformants, engineered to express sgB4 and CP subunits either transiently (sgB4Trans and CPTrans) or in replication-dependent transcription and translation when complemented with gB1 and gB2 (sgB4Rep and CPRep), were mixed in all four pair-wise combinations and infiltrated to Nicotiana benthamiana leaves to systematically evaluate requirements regulating sgB4 packaging. The data revealed that (i) in the absence of replication, packaging was nonspecific, since transiently expressed CP subunits efficiently packaged ubiquitous cellular RNA as well as transiently expressed sgB4 and its deletion variants; (ii) induction of viral replication increased specificity of RNA packaging; and most importantly, (iii) efficient packaging of sgB4, reminiscent of the wt scenario, is functionally coupled not only to its transcription via replication but also to translation of CP from replication-derived mRNA, a mechanism that appears to be conserved among positive-strand RNA viruses of plants (this study), animals (flock house virus), and humans (poliovirus).

* Corresponding author. Mailing address: Department of Plant Pathology, University of California, Riverside, CA 92521-0122. Phone: (951) 827-3810. Fax: (951) 827-4294. E-mail: arao{at}ucr.edu.

Journal of Virology, October 2006, p. 10096-10108, Vol. 80, No. 20
0022-538X/06/$08.00+0     doi:10.1128/JVI.01186-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Yi, G., Kao, C. (2008). cis- and trans-Acting Functions of Brome Mosaic Virus Protein 1a in Genomic RNA1 Replication. J. Virol. 82: 3045-3053 [Abstract] [Full Text]  
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