Infectious Full-Length Clones of Calibrachoa Mottle Virus (CbMV)

Calibrachoa mottle virus (CbMV) infects Calibrachoa, an important new horticultural plant in Europe and in the United States [1]. It belongs to the genus Carmovirus of family Tombusviridae and has a single stranded, positive-sense RNA genome of 3.919 kb (Genbank accession number GQ244431) [2]. Molecular analysis of the CbMV genomic sequence revealed the presence of at least five open reading frames (ORFs) flanked by a short (34 nt) 5’ untranslated region (UTR) and 234 nt non polyadenylated 3’ UTR. The first 5’ proximal ORF (ORF1) encodes a protein of 28 kDa (p28) and terminates with an amber stop codon, whose readthrough would result in the synthesis of a protein of 87 kDa (ORF2; p87) that encloses the motifs of the viral RNA dependent-RNA polymerase (RdRp) [2]. A comparison of amino acid sequences of CbMV with other carmoviruses has shown that both these proteins are involved with expression and/or regulation of the RdRp domain in viruses [3-5]. In vitro translation studies of Carnation mottle virus (CarMV) [6,7] showed that these two ORFs were expressed from the viral genomic RNA. Two small centrally located ORFs encode overlapping proteins of approximately 8 kDa (p8) and 9 kDa (p9), respectively. These proteins have been shown in Turnip crinkle virus (TCV) to be involved with viral cell-to-cell movement (movement proteins or MPs) [3]. The 3’ proximal ORF5 encodes viral coat protein (CP) of 37 kDa (p37). There is no evidence for the presence of cap at 5’ end of carmovirus genomes.