A Non-capsid Protein Associated with Unencapsidated Virus RNA in Barley Infected with Barley Stripe Mosaic Virus

Abstract

SUMMARYBarley tissue with an acute systemic infection of barley stripe mosaic virus contained a large amount of unencapsidated virus RNA which was stable in extracts made in ribosome isolation buffer. The virus RNA in ribosome preparations sedimented in a broad band at 80S to 100S in sucrose gradients, which is less than the virion sedimentation rate of 180S to 200S.

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

“…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).…”

“…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).…”

“…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).…”

Helical capsids of plant viruses: architecture with structural lability

“…In these viruses, the transport form of the virus genome is assumed to be a non-virion RNP, as has been reported for well-studied TMV and BSMV (Brakke et al, 1988;Citovsky et al, 1990Citovsky et al, , 1992. Therefore, the rod-shaped helical virus particles seem to be incompatible with the virion translocation through plasmodesmata, and viruses with such type of virions necessarily encode an MP capable of forming transport RNPs, either the MP of TMV type or the N-terminally-extended TGB1 protein (for details, see Morozov & Solovyev, 2003).…”