Summary auto-generated
This study reports the complete 16,934 nucleotide genome sequence of little cherry virus (LChV), a mealybug-transmitted closterovirus that causes little cherry disease in ornamental and sweet cherry trees worldwide. Researchers cloned and sequenced the 5' terminal region (8,597 nucleotides) from double-stranded RNA, completing the genome sequence using previously determined 3' terminal sequence data. The genome is monopartite and contains open reading frames encoding replication-associated proteins (methyltransferase, RNA helicase, and RNA-dependent RNA polymerase) and structural proteins typical of closteroviruses. The replicase is likely expressed as a 318 kilodalton fusion protein via ribosomal frameshifting. The ORF 1a product contains a papain-like cysteine proteinase domain with predicted cleavage between amino acids 619 and 620. Phylogenetic analysis of RNA polymerase sequences revealed that aphid-transmissible and whitefly-transmissible closteroviruses form distinct evolutionary lineages, with mealybug-transmitted LChV representing the most divergent member of the whitefly virus lineage.
Key findings
- Complete LChV genome sequence determined at 16,934 nucleotides, intermediate in size between beet yellows virus and citrus tristeza virus
- Genome contains ORFs 1a and 1b in 0/-1 frameshift configuration encoding replication proteins, with predicted 318 kDa fusion replicase expression
- Papain-like cysteine proteinase domain identified in ORF 1a product with cleavage site between Gly-619 and Ser-620, yielding a 69 kilodalton leader protein
- Phylogenetic analysis reveals two distinct closterovirus lineages: aphid-transmissible (BYV, BYSV, CTV) and whitefly-transmissible (LIYV, SPSVV, CCSV) closteroviruses, with mealybug-transmitted LChV as the most remote whitefly-lineage member
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Abstract
The 5'-terminal genomic region (8597 nt) of little cherry virus (LChV), a mealybug-borne closterovirus, was cloned from double-stranded RNA, and its sequence determined to complete the 16934 nt sequence of the monopartite LChV RNA genome. In the 5' to 3' direction, the sequence encompasses ORF 1a, encoding the conserved replicative domains of methyltransferase and helicase, and ORF 1b, encoding RNA polymerase. ORFs 1a and 1b partially overlap (in O/+1 configuration), and the LChV replicase is probably expressed by ribosomal frameshifting as a fusion product with a molecular mass of 318 kDa. The N-terminal part of the ORF 1a product contains a papain-like cysteine proteinase (PCP) domain with a predicted cleavage site between Gly-619 and Ser-620. The PCP and the upstream protein domains can be aligned with the equivalent parts of the leader proteins encoded by the whitefly-transmitted lettuce infectious yellows and sweet potato sunken vein closteroviruses. Phylogenetic reconstruction based on the aligned RNA polymerase sequences clearly suggests that the aphid-transmissible and whitefly- transmissible closteroviruses represent two distinct evolutionary lineages, with the mealybug-transmissible LChV being the most remote member of the 'whitefly' lineage.