Characterization and sequence analysis of half of genome RNA of a new Tobamovirus (Cactus mild mottle virus) from cultivated cactus plants in Korea

A new isolate of rod-shaped virus was identified from grafted cactus, Gymnocalycium mihanovichii grafted onto Hylocereus trigonus, in Korea. The virus proved to be a new Tobamovirus and called previously as Tobamovirus-Ca for which we suggest the name Cactus mild mottle virus(CMMoV), because it produced systemic mild mosaic symptoms on its original host. CMMoV is distantly related to known species of the genus Tobamovirus on the basis of host range, serological and sequence analyses. Western blot analysis showed that CMMoV is serologically unrelated to Summons' Opuntia virus which is the only known species of the genus found in cactus plants. The 3'-terminal 2,910 nucleotides have been sequenced for the virus. The coat protein (CP) and movement protein (MP) genes encode 161 and 306 amino acids residues, respectively. The nucleotide and amino acid sequences of the CP were 39.6 ％ to 49.2 ％ and 26.4 ％ to 40.3 ％ identical to other tobamoviruses, respectively. The MP and 3' noncoding region shared 16.3 ％ to 23.3 ％ and 44.6 ％ to 63.4 ％ identities, respectively, with the members of the genus. Phylogenetic tree analysis of the CP gene revealed that CMMoV clusters with members of subgroup I of Tobamovirus. CMMoV particles contained genomic RNA along with two subgenomic RNAs, and this characteristics is common in the members of the subgroup II. This is the first information of sequence and comparative analysis of a Tobamovirus that infects cactus.