Hordeivirus Replication, Movement, and Pathogenesis

Abstract

The last Hordeivirus review appearing in this series 20 years ago focused on the comparative biology, relationships, and genome organization of members of the genus ( 68 ). Prior to the 1989 review, useful findings about the origin, disease occurrence, host ranges, and general biological properties of Barley stripe mosaic virus (BSMV) were summarized in three comprehensive reviews ( 26, 67, 107 ). Several recent reviews emphasizing contemporary molecular genetic findings also may be of interest to various readers ( 15, 37, 42, 69, 70, 88, 113 ). In the current review, we briefly reiterate the biological properties of the four members of the Hordeivirus genus and describe advances in our understanding of organization and expression of the viral genomes. We also discuss the infection processes and pathogenesis of the most extensively characterized Hordeiviruses and frame these advances in the broader context of viruses in other families that have encoded triple gene block proteins. In addition, an overview of recent advances in the use of BSMV for virus-induced gene silencing is presented.

Domain organization of the N-terminal portion of hordeivirus movement protein TGBp1

“…Hordeiviral genomic RNAs form RNP complexes containing TGBp1 as the major if not the sole protein component (Brakke et al, 1988;Lim et al, 2008;Jackson et al, 2009). As shown in vitro, two RNA-binding activities of hordeivirus TGBp1 can be involved in the formation of such RNPs, namely those specified by the C-terminal NTPase/helicase domain and the two clusters of positively charged amino acid residues in the protein N-terminal extension region (Donald et al, 1997;Kalinina et al, 2001).…”

“…The opposite pole is occupied by hordeiviruses characterized by the longest known TGBp1 N-terminal extension region. In this case, the CP is dispensable for both cell-tocell and systemic viral movement, which is believed to occur in the form of RNP complexes containing TGBp1 and genomic RNAs (Brakke et al, 1988;Petty & Jackson, 1990;Lim et al, 2008;Jackson et al, 2009). Between the two extremes are BNYVV (genus Benyvirus) and PCV (genus Pecluvirus) with TGBp1 characterized by a shorter N-terminal extension region comprising the ID and a truncated NTD (Morozov & Solovyev, 2003).…”

“…Viruses with hordei-like TGB, in contrast to viruses with potex-like TGB, require no coat protein for viral cell-to-cell and long-distance transport (Petty & Jackson, 1990;Morozov & Solovyev, 2003). Analysis of RNA-protein complexes isolated from plants infected with barley stripe mosaic virus (BSMV; the type member of the genus Hordeivirus) demonstrated that TGBp1 is the major if not the only protein that interacts with viral genomic and subgenomic RNAs in infected cells to form ribonucleoprotein (RNP) complexes (Brakke et al, 1988;Lim et al, 2008;Jackson et al, 2009). Such TGBp1-RNA complexes are considered to be a form of viral genome capable of cell-to-cell and long-distance transport in plants (Morozov & Solovyev, 2003;Lim et al, 2008).…”

“…The TGB is a conserved module of overlapping genes found in a number of virus groups (Morozov & Solovyev, 2003). Hordeivirus TGBp1 binds viral genomic RNA forming a cell-to-cell transportcompetent complex (Brakke et al, 1988;Kalinina et al, 2001;Lim et al, 2008;Jackson et al, 2009). TGBp2 and TGBp3 are small membrane proteins necessary for intracellular transport of complexes containing TGBp1 and viral RNA to plasmodesmata (Morozov & Solovyev, 2003;Zamyatnin et al, 2004; Haupt et al, 2005;Jackson et al, 2009 Lim et al, 2008;Jackson et al, 2009).…”

Brachypodium as an emerging model for cereal–pathogen interactions

“…BSMV infects several other cereals naturally, and a range of plant species (including some dicots) under experimental conditions (Jackson et al, 2009). While the virus is highly mechanically transmissible facilitating rapid spread in the field, seed transmission is required for survival across seasons.…”