The chimeric nature of the genome of pea enation mosaic virus: the independent replication of RNA 2.
The genome of pea enation mosaic virus (PEMV) consists of two plus-sense RNAs, both of which are required for mechanical transmission. RNA 1 (5706 nucleotides) has strong sequence similarity with members of the luteovirus group, a similarity that is also manifested in the symptomatology, cytopathology and vector transmission of this virus. RNA 2 (4253 nucleotides) is hypothesized to facilitate systemic invasion and mechanical transmission, attributes that distinguish PEMV from the phloem-limited luteoviruses. Sequence analysis of RNA 2 has demonstrated that PEMV is unique among multicomponent viruses in that it lacks 3'- and 5'-terminal homology between its genomic RNAs. Sequence analysis of RNA 2 has identified an open reading frame encoding a putative product of 65K that contains a series of polymerase-like motifs typical of viral RNA-dependent RNA polymerases. This protein sequence lacks homology with the polymerase encoded on RNA 1 of PEMV, instead being more closely affiliated with the polymerases of viruses related to the carmo- and tombusvirus groups. Inoculation of pea protoplasts with RNA transcripts derived from a full-length cDNA clone of RNA 2 has demonstrated that RNA 2 replicates autonomously in the absence of RNA 1, although comparable inoculation of whole plants failed to establish a systemic infection. There is no evidence that RNA 2 encodes structural proteins, suggesting that encapsidation functions are supplied in trans by RNA 1, comparable to the helper-dependent complexes occurring within the luteovirus group. These data suggest that the PEMV genome can be characterized as a symbiotic association of two taxonomically distinct viral RNAs cooperatively interacting in the establishment of a systemic virus infection.
Demler
S A
SA
Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824-1312.
Rucker
D G
DG
de Zoeten
G A
GA
D000595:Amino Acid Sequence; D001483:Base Sequence; D007887:Fabaceae / Q000382:microbiology*; D016679:Genome, Viral; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D009029:Mosaic Viruses / Q000235:genetics*; D016366:Open Reading Frames / Q000235:genetics; D010946:Plants, Medicinal; D012367:RNA, Viral / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D014764:Viral Proteins / Q000235:genetics; D014779:Virus Replication / Q000235:genetics / Q000502:physiology
D012367:RNA, Viral; D014764:Viral Proteins