Cactus mild mottle virus is a new cactus-infecting tobamovirus

A new cactus-infecting tobamovirus, Cactus mild mottle virus (CMMoV), was isolated from diseased grafted cactus, Gymnocalycium mihanovichii and its molecular properties were characterized. CMMoV is distantly related to known species of the genus Tobamovirus on the basis of serological and sequence analyses. Western blot analysis showed that CMMoV is serologically unrelated to Sammon's Opuntia virus, which is the only known species of the genus Tobamovirus found in cactus plants. The 3'-terminal 2,910 nucleotides of CMMoV have been sequenced. The coat protein (CP) and movement protein (MP) genes encode 161 and 306 amino acids residues, respectively, and the 3' untranslated region (UTR) consists of 229 nucleotides long. The nucleotide and amino acid sequences of the CP of CMMoV were 39.6% to 49.2% and 25.8% to 40.3% identical to other seventeen tobamoviruses, respectively. The MP shared 34.9% to 40.6% and 16.3% to 27.0% and 44.6% to 63.4% identities, respectively, at the amino acid and nucleotide levels with other members of the genus. Percentage identities of nucleotides of the 3' UTR ranged from 42.5% to 63.4%. Phylogenetic tree analyses of the CP and MP suggest the existence of the fifth cactus-infecting subgroup in the genus Tobamovirus. Sequence analyses of these two viral proteins revealed that the highest amino acid sequence identity between the virus and seventeen other tobamoviruses was 40.6%, supporting the view that CMMoV is a new definite species of the genus Tobamovirus.