The nucleotide sequence and genomic organization of Citrus leaf blotch virus: Candidate type species for a new virus genus

The complete nucleotide sequence of Citrus leaf blotch virus (CLBV) was det ermined. CLBV genomic RNA (gRNA) has 8747 nt, excluding the 3'-terminal pol y(A) tail, and contains three open reading frames (ORFs) and untranslated r egions (UTR) of 73 and 541 nucleotides at the 5' and 3' termini, respective ly. ORF1 potentially encodes a 227.4-kDa polypeptide, which has methyltrans ferase, papain-like protease, helicase, and RNA-dependent RNA polymerase mo tifs. ORF2 encodes a 40.2-kDa polypeptide containing a motif characteristic of cell-to-cell movement proteins. The 40.7-kDa polypeptide encoded by ORF 3 was identified as the coat protein. The genome organization of CLBV resem bles that of viruses in the genus Trichovirus, but they differ in various a spects: (i) in trichoviruses ORF2 overlaps ORFs 1 and 3, whereas in CLBV, O RFs 2 and 3 are separated and ORFs 1 and 2 overlap in one nucleotide; (ii) CLBV gRNA and CP are larger than those of trichoviruses; and (iii) the CLBV 3' UTR is larger than that of trichoviruses. Phylogenetic comparisons base d on CP amino acid signatures clearly separates CLBV from trichoviruses. Al so contrasting with trichoviruses, CLBV could not be transmitted to Chenopo dium quince Willd. Considering these singularities, we propose that CLBV sh ould be included in a new virus genus. (C) 2001 Academic Press.