Molecular characterization and coat protein serology of watermelon leaf mottle virus (Potyvirus)

A cDNA library was generated from purified RNA of watermelon leaf mottle vi rus (WLMV) (Genus Potyvirus). Two overlapping clones totaling 2,316 nucleot ides at the 3' terminus of the virus were identified by immunoscreening wit h coat protein antiserum. The sequence analyses of the clones indicated an open reading frame (ORF) of 2,050 nucleotides which encoded part of the rep licase and the coat protein, a 243-nucleotide non-coding region (3'UTR), an d 23 adenine residues of the poly (A) tail. The taxonomic status of WLMV wa s determined by comparisons of the sequence of the cloned coat protein gene and 3'UTR with potyvirus sequences obtained from GenBank. The nucleotide s equence identities of WLMV compared with 17 other potyviruses ranged from 5 5.6 to 63.5% for the coat protein, and from 37.2 to 48.3% for the 3'UTR. Ph ylogenetic analyses of the coat protein region and the 3'UTR indicated that WLMV did not cluster with other potyviruses in a clade with high bootstrap support. The coat protein gene was expressed in Escherichia coli and a pol yclonal antiserum was prepared to the expressed coat protein. In immunodiff usion tests, WLMV was found to be serologically distinct from papaya ringsp ot virus type W, watermelon mosaic virus 2, zucchini yellow mosaic virus, a nd Moroccan watermelon mosaic virus. In Western blots and ELISA, serologica l cross-reactivity with other cucurbit potyviruses was observed. Serologica l and sequence comparisons indicated that watermelon leaf mottle virus is a distinct member of the Potyvirus genus.