ISHS Acta Horticulturae 568: X International Symposium on Virus Diseases of Ornamental Plants
GENOME ORGANIZATION OF PELARGONIUM CHLOROTIC RING PATTERN VIRUS: FURTHER IMPLICATIONS FOR TOMBUSVIRIDAE TAXONOMY |
| Authors: | G. Kinard, R. Jordan |
| Keywords: | geranium, isolate GR57, carmovirus, pelarspovirus |
| DOI: | 10.17660/ActaHortic.2002.568.1 |
| Abstract:
The geranium virus isolate “Gr57” was described as causing vein banding and leaf distortion of zonal geranium in Italy, and being serologically related to Pelargonium ringspot virus (PelRSV). We have determined the nucleotide sequence of Gr57, and have shown that it is distinct from PelRSV; the name Pelargonium chlorotic ring pattern virus (PCRPV) is proposed. The genome consists of at least 3904 nucleotides and the positive strand contains five open reading frames (ORFs) that may be expressed. The 5' proximal ORF encodes a 27k protein (p27) terminating with an amber codon that may be read through to produce an 87k protein (p87). Two small centrally located ORFs encode a 7k (p7) and a 9k (p9) protein respectively, while the 3' proximal ORF encodes the 37kDa coat protein (CP). The genomic organization of PCRPV, its probable translation strategy, and predicted amino acid sequences most closely resemble those of known carmoviruses, but there are several important distinctions. Double?stranded RNA analysis and hybridization assays reveal only one subgenomic RNA (sgRNA) in infected plants, while carmoviruses express two sgRNAs. The PCRPV sgRNA has the potential to encode the p7, p9, and coat proteins. The p7 and p9 have similarity to ORFs of carmo?, necro-, panico?, and machlomoviruses thought to be involved in virus spread. Whereas the carmovirus p7 and p9 homologs are expressed as overlapping, out-of-frame genes from the larger sgRNA (and the CP from a second smaller sgRNA), the arrangement and coding of the PCRPV p7 and p9 from PCRPV ORFs suggest that they are expressed as a p13 fusion protein as a result of a ?1 frameshift mechanism. Comparisons to Pelargonium line pattern virus (PLPV), Elderberry latent virus (ELV), and PelRSV, revealed amino acid identities ranging from about 45% (CP) to 56% (RdRp). These percentages are at least 10% higher identity levels than to genes of carnation mottle, turnip crinkle, and saguaro cactus carmoviruses. Thus, PCRPV appears to be distinct from, but to cluster with, PLPV, PelRSV, and ELV, which also express a single subgenomic RNA species. The overall properties of these four viruses indicate that they are related, but distinct from each other, and differ sufficiently from previously described Tombusviridae members to be recognized as members of a new genus for which the name Pelarspovirus is proposed. | |
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