Journal of Virology, September 2001, p. 8712-8723, Vol. 75, No. 18
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.18.8712-8723.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Department of Plant and Microbial Biology, University of California, Berkeley, California 94720
Received 1 March 2001/Accepted 12 June 2001
We have recently used a green fluorescent protein (GFP) fusion to
the
b protein of Barley stripe mosaic virus (BSMV) to
monitor cell-to-cell and systemic virus movement. The
b protein is
involved in expression of the triple gene block (TGB) proteins encoded by RNA
but is not essential for cell-to-cell movement. The GFP fusion appears not to compromise replication or movement substantially, and mutagenesis experiments demonstrated that the three most abundant TGB-encoded proteins,
b (TGB1),
c (TGB3), and
d (TGB2), are each required for cell-to-cell movement (D. M. Lawrence and
A. O. Jackson, Mol. Plant Pathol. 2:65-75, 2001). We
have now extended these analyses by engineering a fusion of GFP to TGB1
to examine the expression and interactions of this protein during
infection. BSMV derivatives containing the TGB1 fusion were able to
move from cell to cell and establish local lesions in Chenopodium
amaranticolor and systemic infections of Nicotiana
benthamiana and barley. In these hosts, the GFP-TGB1 fusion
protein exhibited a temporal pattern of expression along the advancing
edge of the infection front. Microscopic examination of the subcellular
localization of the GFP-TGB1 protein indicated an association with the
endoplasmic reticulum and with plasmodesmata. The subcellular
localization of the TGB1 protein was altered in infections in which
site-specific mutations were introduced into the six conserved regions
of the helicase domain and in mutants unable to express the TGB2 and/or TGB3 proteins. These results are compatible with a model suggesting that movement requires associations of the TGB1 protein with
cytoplasmic membranes that are facilitated by the TGB2 and TGB3 proteins.
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