title: The DNA-B of the non-phloem-limited bean dwarf mosaic virus (BDMV) is able to move the phloem-limited Abutilon mosaic virus (AbMV) out of the phloem, but DNA-B of AbMV is unable to confine BDMV to the phloem.
abstract: Abutilon mosaic virus (AbMV) and bean dwarf mosaic virus (BDMV) are two phylogenetically related bipartite begomoviruses. While AbMV is restricted to phloem, BDMV spreads to non-phloem tissues. Cell-to-cell and long-distance movement of AbMV and BDMV were investigated after replacing the coat protein (CP) gene with the reporter gene encoding the green fluorescence protein (GFP). The DNA-A and DNA-B genomic components of AbMV and BDMV, and their pseudorecombinants (PR), were delivered to bean (Phaseolus vulgaris) seedlings and detached leaves with DNA-coated microprojectiles. Virus-associated fluorescence was observed with the confocal microscope. Delivery of AbMV and BDMV GFP reporters showed that the epidermal tissue was the main recipient of the viral DNA; the DNA-A of the two viruses was unable to move out of the recipient cells. AbMV DNA-A co-inoculated with AbMV DNA-B did not move from cell to cell in the epidermis and did not reach the phloem. However, co-inoculation of AbMV DNA-A with BDMV DNA-B resulted in PR cell-to-cell movement out of the epidermis and long-distance movement in the phloem. In contrast, BDMV DNA-A moved from cell to cell and over a long distance when co-inoculated with either its own DNA-B or with the DNA-B of AbMV. Thus, the DNA-B of the non-phloem-limited BDMV overcame the phloem limitation of AbMV. In the reciprocal case, the DNA-B of the phloem-limited AbMV did not confine the non-phloem limited BDMV to the phloem. Hence, we assume that the DNA-A component of BDMV includes determinants involved in the movement pattern of the virus in addition to the DNA-B-encoded BC1 and BV1 which have previously been shown to be involved in virus movement. The results also confirm that the CP is not necessary for virus movement; however, replacing the CP of AbMV and BDMV with GFP resulted in a decrease in symptom severity. DNA-B was involved in symptom severity; the B component of BDMV produced symptoms more severe than those induced by that of AbMV, whether in wild-type PRs or in PRs with CP-GFP replacement. It is interesting to note that when the GFP gene under the control of the CaMV 35S promoter (35S-GFP) was delivered to the bean tissue, with or without the DNA-B component of BDMV, GFP was expressed but did not move from cell to cell. However, when the 35S-GFP was delivered together with BDMV DNA-A and DNA-B, GFP showed cell-to-cell movement in the epidermis but was restricted to these cells. Hence, infection of cells with a functional bipartite begomovirus may facilitate cell-to-cell movement of macromolecules.
authors.affiliation: Robert H. Smith Institute of Plant Sciences and Genetics, Faculty of Agriculture, Hebrew University of Jerusalem, Rehovot 76100, Israel.
authors.forename: Avner
authors.initials: A
authors.lastname: Levy
authors.forename: Henryk
authors.initials: H
authors.lastname: Czosnek
mesh_terms: D019470:Biolistics; D001692:Biological Transport; D015139:Blotting, Southern; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004279:DNA, Viral / Q000235:genetics / Q000378:metabolism*; D007887:Fabaceae / Q000166:cytology / Q000378:metabolism / Q000821:virology*; D017791:Geminiviridae / Q000235:genetics / Q000378:metabolism*; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D018613:Microscopy, Confocal; D018515:Plant Leaves / Q000166:cytology / Q000378:metabolism / Q000821:virology; D018514:Plant Structures / Q000378:metabolism* / Q000821:virology; D016133:Polymerase Chain Reaction; D011993:Recombinant Fusion Proteins / Q000008:administration & dosage / Q000235:genetics / Q000378:metabolism
chemical_list: D004279:DNA, Viral; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins