Cucumber Mosaic Virus

Abstract

Cucumber mosaic virus (CMV) is the type member of the genus Cucumovirus in the family Bromoviridae. CMV has a worldwide distribution and a host range of over 1300 plant species. The virus is transmitted by about 80 species of aphid in a nonpersistent manner. CMV is also transmitted through the seed with variable, but usually low, efficiencies. The CMV genome consists of three, single-stranded, positive-sense RNAs, encoding five proteins. The three genomic RNAs are packaged separately into isometric particles of 29 nm diameter (T = 3 symmetry), while RNA3 is co-packaged with subgenomic RNA4. The 1a and 2a proteins are involved primarily in virus replication occurring on tonoplast membranes, while the 2b, 3a, and 3b (capsid) proteins are involved in virus movement. The 2b protein is an inhibitor of plant defense responses. Different isolates of CMV induce a variety of disease responses, which are attenuated by a satellite RNA associated with some isolates of CMV, although some satellite RNAs can enhance pathogenicity. Control of CMV has been achieved to a limited extent by use of transgenic plants expressing viral sequences, but due to the considerable sequence diversity of this virus, natural resistance genes do not give broad-spectrum resistance.