Characterization of Cucumber Mosaic Virus

AbstractTo ascertain the importance of amino-terminal proximal capsid protein (CP) sequences in cell-to-cell movement, virion formation, and stabilization, two CP mutants of cucumber mosaic virus (CMV) were generated by deletion of sequences encoding CP amino acids 15–40 (ΔSal-Nru) or 26–40 (ΔSac-Nru). Wildtype CMV and CMV containing ΔSac-Nru could infect systemically four host species, although symptoms induced by the two viruses usually were different. CMV containing ΔSal-Nru could only infectNicotiana benthamianaandN. clevelandiisystemically, but only slowly, suggesting phloem-independent long-distance movement. A variant mutant designated ΔSal-Nru* could systemically infectN. tabacumas well as the above twoNicotianaspecies, rapidly, but could not systemically infectCucurbita pepo.Virus particles could not be detected in plants infected by ΔSal-Nru, while ΔSal-Nru* and ΔSac-Nru formed particles of lower stabilities than for wildtype virus. The CPs of ΔSal-Nru and ΔSal-Nru* could bind RNAin vitro,although less strongly than ΔSac-Nru or wildtype CMV. These data indicate that amino-terminal proximal sequences of the CMV CP interact with viral RNA and are required for the formation of stable virions. Moreover, while the CP is necessary for cell-to-cell movement, the ability to form virions is not a prerequisite for cell-to-cell movement