The Genetics and Genomics of Virus Resistance in Maize

Viruses cause significant diseases on maize worldwide. Intensive agronomic practices, changes in vector distribution, and the introduction of vectors and viruses into new areas can result in emerging disease problems. Because deployment of resistant hybrids and cultivars is considered to be both economically viable and environmentally sustainable, genes and quantitative trait loci for most economically important virus diseases have been identified. Examination of multiple studies indicates the importance of regions of maize chromosomes 2, 3, 6, and 10 in virus resistance. An understanding of the molecular basis of virus resistance in maize is beginning to emerge, and two genes conferring resistance to sugarcane mosaic virus, Scmv1 and Scmv2, have been cloned and characterized. Recent studies provide hints of other pathways and genes critical to virus resistance in maize, but further work is required to determine the roles of these in virus susceptibility and resistance. This research will be facilitated by rapidly advancing technologies for functional analysis of genes in maize

Taxonomy of the family Arenaviridae and the order Bunyavirales : update 2018

In 2018, the family Arenaviridae was expanded by inclusion of 1 new genus and 5 novel species. At the same time, the recently established order Bunyavirales was expanded by 3 species. This article presents the updated taxonomy of the family Arenaviridae and the order Bunyavirales as now accepted by the International Committee on Taxonomy of Viruses (ICTV) and summarizes additional taxonomic proposals that may affect the order in the near future.Peer reviewe

Tomato ringspot nepovirus protease: characterization and cleavage site specificity

We have cloned the region of tomato ringspot nepovirus (TomRSV) RNA-1 coding for the putative TomRSV 3C-related protease (amino acids 1213 to 1508) in a transcription vector and in a transient expression vector. Using cell-free transcription and translation systems and plant protoplasts, we have demonstrated that proteins produced from these clones possess a proteolytic activity in trans on the cleavage site between the TomRSV movement and coat proteins. By amino acid homology of the TomRSV 3C-related protease with other nepo- and comovirus proteases, His1283, Glu1331 (or Asp1354) and Cys1433 have been predicted to constitute the catalytic triad. Site-directed mutagenesis of His1283 to Asp abolished the TomRSV protease activity, in vitro and in vivo. The cleavage site between the TomRSV movement and coat proteins has been determined to be Q/G, by direct protein sequencing. Previously, His1451 located in the substrate binding pocket of the TomRSV 3C-related protease has been suggested to be involved in the cleavage site specificity. We show that an inactive TomRSV 3C-related protease is obtained after substitution of His1451 with Leu. These results are discussed in light of the possible relation of the TomRSV 3C-related protease to 3C-related proteases of nepo-, como- and potyviruses

Expression of the tomato ringspot nepovirus movement and coat proteins in protoplasts

Tomato ringspot nepovirus (TomRSV) produces a 45 kDa movement protein and a 58 kDa coat protein in infected plants. Accumulation of the movement protein in relation to that of the coat protein was studied in infected protoplasts using a monoclonal antibody against the movement protein and polyclonal antibodies against the coat protein. Unlike most other viral movement proteins, the TomRSV movement protein was present at late stages of infection. Pulse-chase labelling experiments revealed that the release of the movement protein from the precursor polyprotein was coordinated with that of the coat protein. However, the movement protein was less stable than the coat protein in the extractable fraction of the protoplasts. The expression pattern of the TomRSV movement protein is discussed in the light of the proposed mechanism of cell-to-cell movement of virus-like particles through tubular structures composed of the movement protein