Role of cucumovirus capsid protein in long-distance movement within the infected plant

Abstract

Direct evidence is presented for a host-specific role of the cucumovirus capsid protein in long-distance movement within infected plants. Cucumber (Cucumis sativus L.) is a systemic host for cucumber mosaic cucumovirus (CMV). Tomato aspermy cucumovirus, strain 1 (1-TAV), multiplied to the levels of CMV (i.e., replicated, moved from cell to cell, and formed infectious particles) in the inoculated leaves of cucumbers but was completely unable to spread systemically. The defective long-distance systemic movement of 1-TAV was complemented by CMV in mixed infections. Coinfection of cucumbers with 1-TAV RNA with various combinations of transcripts from full-length cDNA clones of CMV genomic RNA 1, RNA2, and RNA3 showed that CMV RNA3 alone complemented 1-TAV long-distance movement. We obtained mutants containing mutations in the two open reading frames in CMV RNA3 encoding the 3a protein and the capsid protein (CP), both of which are necessary for cell-to-cell movement of CMV. Complementation experiments with mutant CMV RNA3 showed that only 3a protein mutants, i.e., those with an intact CP, complemented the long-distance movement of 1-TAV in cucumbers. Since CMV and TAV have common systemic host plants, the results presented here are strong evidence for an active, host-specific function of the CPs of these two cucumoviruses for long-distance spread in the phloem. The results also suggest that the plasmodesmata in the vascular system and/or at the boundary between the mesophyll and the vascular system, involved in long-distance movement through the phloem, and those in the mesophyll, involved in cell-to-cell movement, differ functionally.

A novel naturally occurring hybrid gene encoded by a plant RNA virus facilitates long distance virus movement.

“…It has been shown that the 3a protein potentiates cell-to-cell trafficking of CMV RNA in tobacco plants (Ding,B. et al, 1995) and that the CMV CP is able to complement the defective long distant movement of tomato aspermy cucumovirus (TAV) in cucumber plants (Taliansky and Garcia-Arenal, 1995). We have previously identified a novel gene (2b) encoded by the cucumovirus group but which is absent in closely related viruses, such as the bromoviruses and alfalfa mosaic virus (Ding,S.…”

An Introduction to the Evolutionary Ecology of Viruses

“…MPs have been identified in many plant viruses, but the biochemical and molecular mechanisms involved unfortunately are largely unknown. MPs are frequently capsid proteins, as has been demonstrated in tobacco mosaic virus (Dawson et al, 1988;Saito et al, 1990), red clover necrotic mosaic dianthovirus (Xiong et al, 1993;Vaewhongs and Lommel, 1995), cucumber mosaic virus (CMV) (Taliansky and Garcia-Arenal, 1995), and tobacco etch potyvirus (Dolja et al, 1994(Dolja et al, , 1995, among others. Replication proteins such as those involved in genome duplication have also been identified as necessary for long-distance movement in brome mosaic virus (Traynor et al, 1991) and CMV (Gal-On et al, 1994).…”

Transcomplementation and synergism in plants: implications for viral transgenes?

“…Cucumovirus (Cooper et al, 1996;Kaplan et al, 1995) Bromovirus (Nagano et al, 2001) Tobamovirus (Tamai et al, 2003) Potexvirus (Tamai et al,2003) Cucumovirus (Teycheney et al, 2000) Cucumovirus (Salanki et al, 1997;Taliansky and Garcia-Arenal, 1995) Potexvirus (Brigneti et al, 1998) Tobravirus (Liu et al, 2002) Potyvirus (Ryang et al, 2004) Closterovirus (Chiba et al, 2006) Begomovirus (Wege and Siegmund, 2007) Comovirus (Malyshenko et al, 1989) Potyvirus (Guerini and Murphy, 1999;Murphy and Kyle, 1995) Potexvirus (Close, 1964) Cucumovirus…”