TL;DR: The theory of a cellular self-replicating mRNA as the origin of totiviruses is attractive because of their apparent ancient origin, the close relationships among their RDRPs, genome simplicity and the ability to use host proteins efficiently.
Abstract: Fungal viruses or mycoviruses are widespread in fungi and are believed to be of ancient origin. They have evolved in concert with their hosts and are usually associated with symptomless infections. Mycoviruses are transmitted intracellularly during cell division, sporogenesis and cell fusion, and they lack an extracellular phase to their life cycles. Their natural host ranges are limited to individuals within the same or closely related vegetative compatibility groups. Typically, fungal viruses are isometric particles 25-50 nm in diameter, and possess dsRNA genomes. The best characterized of these belong to the family Totiviridae whose members have simple undivided dsRNA genomes comprised of a coat protein (CP) gene and an RNA dependent RNA polymerase (RDRP) gene. A recently characterized totivirus infecting a filamentous fungus was found to be more closely related to protozoan totiviruses than to yeast totiviruses suggesting these viruses existed prior to the divergence of fungi and protozoa. Although the dsRNA viruses at large are polyphyletic, based on RDRP sequence comparisons, the totiviruses are monophyletic. The theory of a cellular self-replicating mRNA as the origin of totiviruses is attractive because of their apparent ancient origin, the close relationships among their RDRPs, genome simplicity and the ability to use host proteins efficiently. Mycoviruses with bipartite genomes (partitiviruses), like the totiviruses, have simple genomes, but the CP and RDRP genes are on separate dsRNA segments. Because of RDRP sequence similarity, the partitiviruses are probably derived from a totivirus ancestor. The mycoviruses with unencapsidated dsRNA-like genomes (hypoviruses) and those with bacilliform (+) strand RNA genomes (barnaviruses) have more complex genomes and appear to have common ancestry with plant (+) strand RNA viruses in supergroup 1 with potyvirus and sobemovirus lineages, respectively. The La France isometric virus (LIV), an unclassified virus with multipartite dsRNA genome, is associated with a severe die-back disease of the cultivated mushroom. LIV appears to be of recent origin since it differs from its host in codon usage.
TL;DR: A silencing suppressor protein (SSP), P0(PE), is identified in the Enamovirus Pea enation mosaic virus-1 (PEMV-1) and it is shown that it and the P0s of poleroviruses Potato leaf roll virus and Cereal yellow dwarf virus have strong local and systemic SSP activity.
TL;DR: The hypothesis that RYMV originated in East Africa and then dispersed and differentiated gradually from the east to the west of the continent is supported.
Abstract: Fourteen isolates of Rice yellow mottle virus (RYMV) were selected as representative of the genetic variability of the virus in Africa from a total set of 320 isolates serologically typed or partially sequenced. The 14 isolates were fully sequenced and analyzed together with two previously reported sequences. RYMV had a genomic organization similar to that of Cocksfoot mottle sobemovirus. The average nucleotide diversity among the 16 isolates of RYMV was 7%, and the maximum diversity between any two isolates was 10%. A strong conservative selection was apparent on both synonymous and nonsynonymous substitutions, through the amino acid replacement pattern, on the genome size, and through the limited number of indel events. Furthermore, there was a lack of positive selection on single amino acid sites and no evidence of recombination events. RYMV diversity had a pronounced and characteristic geographic structure. The branching order of the clades correlated with the geographic origin of the isolates along an east-to-west transect across Africa, and there was a marked decrease in nucleotide diversity moving westward across the continent. The insertion-deletion polymorphism was related to virus phylogeny. There was a partial phylogenetic incongruence between the coat protein gene and the rest of the genome. Overall, our results support the hypothesis that RYMV originated in East Africa and then dispersed and differentiated gradually from the east to the west of the continent.
TL;DR: In this paper, a silencing suppressor protein (SSP), P0PE, was identified in the Enamovirus Pea enation mosaic virus-1 (PEMV-1) and showed that it and the P0s of poleroviruses Potato leaf roll virus and Cereal yellow dwarf virus have strong local and systemic SSP activity, while the P1 of Sobemovirus Southern bean mosaic virus supresses systemic silencing.
TL;DR: A reverse transcription polymerase chain reaction (RT-PCR) assay has been developed that can simultaneously test a sample, in one tube, for the presence of five seedborne legume viruses that are of great concern to legume germ plasm banks as discussed by the authors.
Abstract: A reverse transcription polymerase chain reaction (RT-PCR) assay has been developed that can simultaneously test a sample, in one tube, for the presence of five seedborne legume viruses that are of great concern to legume germ plasm banks: alfalfa mosaic alfamovirus, bean yellow mosaic potyvirus, clover yellow vein potyvirus, cucumber mosaic cucumovirus, and subterranean clover mottle sobemovirus. RT-PCR assays were also developed for the detection of subterranean clover redleaf luteovirus and subterranean clover stunt virus, thus providing a detection system for all well-characterized viruses known to infect subterranean clover. Primers were designed so that the size of the RT-PCR product was indicative of the virus amplified and, where sequences of more than one strain of virus were available, conserved regions were given preference as primer targets