Molecular studies on bromovirus capsid protein. III. Analysis of cell-to-cell movement competence of coat protein defective variants of cowpea chlorotic mottle virus.
To determine whether the role of coat protein (CP) in cell-to-cell movement of dicot-adapted cowpea chlorotic mottle bromovirus (CCMV) is distinct from that of monocot-adapted brome mosaic bromovirus (BMV), two reporter genes, beta-glucuronidase (GUS) and enhanced green fluorescent protein (EGFP), were substituted for the CP in a biologically active clone of CCMV RNA3 (C3). Primary leaves of Nicotiana benthamiana, Chenopodium quinoa, and cowpea were co-inoculated with wild-type (wt) CCMV RNA 1 and -2 and either C3/delta CP-GUS or C3/delta CP-EGFP and analyzed for GUS activity or the presence of green fluorescence. The visual appearance of infections caused by GUS or EGFP variants indicated that, in CCMV, epidermal cell-to-cell movement can occur without a functional CP. By contrast, inoculation of MP defective variants of C3/delta CP-GUS or C3/delta CP-EGFP resulted in subliminal infections. Additional experiments examining the infectivity of wt BMV RNA 1 and -2 and a BMV RNA3 variant bearing the EGFP in the place of CP (B3/delta CP-EGFP) confirmed previous observations that, unlike CCMV, epidermal cell-to-cell movement of BMV is dependent on the expression of a functional CP. Taken together, the results demonstrate that BMV and CCMV use different mechanisms for initial epidermal cell-to-cell spread, and the individual role played by the respective CP genes in this active process is discussed.
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Department of Plant Pathology, University of California, Riverside 92521-0122, USA. arao@ucrac1.ucr.edu
D017795:Bromovirus / Q000235:genetics / Q000502:physiology*; D002213:Capsid / Q000235:genetics / Q000502:physiology*; D017353:Gene Deletion; D017930:Genes, Reporter; D014644:Genetic Variation; D005966:Glucuronidase / Q000235:genetics; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics; D018532:Pisum sativum; D018515:Plant Leaves / Q000821:virology
D008164:Luminescent Proteins; D049452:Green Fluorescent Proteins; D005966:Glucuronidase