Details

Autor(en) / Beteiligte

• Scott, K.P

Titel

Studies on the genomic components of potato mop-top virus

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

1992

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• Potato mop-top furovirus (PMTV) is a fungus-transmitted virus which has rod-shaped particles and can cause serious damage to tubers of sensitive potato cultivars. Particles of the stock culture, isolate T, were found to contain three RNA species of 6.5, 3.0 and 2.5kb in size. A cDNA library was constructed in the expression vector lambda ZAPII using purified, unfractionated viral RNA as the template. Hybridisation experiments using cDNA probes specific for each of the three RNA species showed that none was derived from another. The sizes of these RNA species in isolates obtained from four European countries and Japan were found to vary, especially that of RNA 3 which was larger in most other isolates than in isolate T. Fusion proteins produced from some of the clones specific for RNA 3 of PMTV-T reacted with PMTV-specific monoclonal antibodies, and the amino-acid sequence encoded by these clones had some similarity to the coat protein sequence of soil-borne wheat mosaic virus (SBWMV), a serologically related furovirus. The nucleotide sequence also contained a stop codon, suppression of which could result in synthesis of a readthrough protein from a following open reading frame (ORF). The sequence of PMTV-T RNA 2 contained three overlapping ORFs known as the triple gene block, which encode proteins that have analogues known to be involved in the cell to cell transport of other viruses. The 5' ORF encodes a 51K protein which contains a putative NTP-binding site. The middle and 3' ORFs respectively encode 13K and 21K proteins each of which has two hydrophobic domains, typical of membrane-associated proteins. All three proteins have amino-acid sequence similarities to proteins encoded by the triple block genes of barley stripe mosaic hordeivirus and beet necrotic yellow vein furovirus. PMTV was detected in field-grown potato plants by two methods. Firstly, specific primers based on the sequence of PMTV-T RNA 2 were used to amplify a im500bp fragment in a reverse transcription-polymerase chain reaction assay. Secondly, cDNA probes specific for individual RNA species were hybridised to Northern blots of total leaf of tuber RNA. A 2.3kb probe specific for PMTV-T RNA 2 also indicated the presence of a smaller, presumably subgenonmic, RNA species of about 1.1kb in some field isolates. A probe specific for PMTV-T RNA 3 showed that there was size variation in RNA 3 in different isolates, even among those obtained from the same area. Possession of a triple gene block differentiates PMTV from SBWMV, the type member of the furovirus group. The apparent location of the coat protein gene and triple gene block on different RNA molecules distinguishes PMTV from BNYVV. Thus the furovirus group, as currently constituted, contains viruses with different genome strategies that should probably be assigned to different groups.