Single amino acid changes in the turnip mosaic virus viral genome-linked protein (VPg) confer virulence towards Arabidopsis thaliana mutants knocked out for eukaryotic initiation factors eIF(iso)4E and eIF(iso)4G

Abstract

Previous resistance analyses of Arabidopsis thaliana mutants knocked out for eukaryotic translation initiation factors showed that disruption of the At-eIF(iso)4E or both the AteIF(iso)4G1 and At-eIF(iso)4G2 genes resulted in resistance against turnip mosaic virus (TuMV). This study selected TuMV virulent variants that overcame this resistance and showed that two independent mutations in the region coding for the viral genome-linked protein (VPg) were sufficient to restore TuMV virulence in At-eIF(iso)4E and At-eIF(iso)4G1¾At-eIF(iso)4G2 knockout plants. As a VPg-eIF(iso)4E interaction has been shown previously to be critical for TuMV infection, a systematic analysis of the interactions between A. thaliana eIF4Es and VPgs of virulent and avirulent TuMVs was performed. The results suggest that virulent TuMV variants may use an eIF4F-independent pathway.The eukaryotic translation initiation factors eIF4E and eIF4G play a key role during virus infection in plants ( Robaglia & Caranta, 2006). During mRNA translation, eIF4E provides the cap-binding function and is associated with eIF4G, the scaffold for the other components of the translation initiation complex, to form the eIF4F complex (Marcotrigiano et al., 1999). In plants, a second eIF4F complex called eIF(iso)4F is present, and results from the assembly of eIF(iso)4E and eIF(iso)4G isoforms (Browning, 2004). These two complexes perform essentially the same task in translation, but have different affinities for certain classes of mRNA substrates and are probably involved in different cellular events (Gallie & Browning, 2001). Plant genes encoding proteins from the eIF4F and eIF(iso)4F complexes belong to small gene families. In Arabidopsis thaliana, three genes encode the eIF4E subfamily proteins (eIF4E1, eIF4E2 and eIF4E3), one encodes eIF(iso)4E and one a non-canonical eIF4E-like protein, known as novel cap-binding protein (nCBP). A single gene encodes eIF4G, whilst two genes encode the eIF(iso)4G subfamily proteins [eIF(iso)4G1 and eIF(iso)4G2] ( Robaglia & Caranta, 2006). Viruses that depend on these factors to perform their infectious cycle include members of the genus Potyvirus, the largest and the most diverse genus of plant viruses (Adams et al., 2005;Shukla et al., 1994). Potyviruses are characterized by a positive-sense, single-stranded RNA genome of about 10 kb that encodes at least ten multifunctional proteins. The genome is 39-polyadenylated and covalently linked at its 59 end to a virus-encoded protein (VPg) (Murphy et al., 1991;Revers et al., 1999).Potyviruses may selectively use either the eIF4E or eIF(iso)4E isoform in A. thaliana to achieve a successful infection (Sato et al., 2005). We have demonstrated that potyviruses, including turnip mosaic virus (TuMV), selectively use members of the eIF4G family in a fashion that parallels the selective recruitment of eIF4E isoforms (Nicaise et al., 2007;Sato et al., 2005 ; data not shown).In order to confirm that each single amino acid change in the VPg cistron of TuMV determined its virulence on the At...

Two Arabidopsis Loci Encode Novel Eukaryotic Initiation Factor 4E Isoforms That Are Functionally Distinct from the Conserved Plant Eukaryotic Initiation Factor 4E

“…While mutations in eIF4E that confer viral resistance are naturally occurring (Robaglia and Caranta, 2006) and directed mutagenesis has further identified residues conferring virus resistance (German-Retana et al, 2008;Ashby et al, 2011), the 15 conserved flowering plant eIF4E residues differing in eIF4E1b-type proteins do not overlap with these residues, with the exception of a K78 mutation, which confers virus resistance in pea (Ashby et al, 2011). Interestingly, transfer DNA (T-DNA) insertion mutants for EIF4E1B or EIF4E1C do not have any effect on turnip mosaic virus infection in Arabidopsis (Gallois et al, 2010). To date, neither EIF4E1B nor EIF4E1C has been reported to be a virus resistance gene in contrast to numerous reports of virus resistance attributed to EIF4E and EIFISO4E alleles (Wang and Krishnaswamy, 2012).…”

Helper Component Proteinase of the Genus Potyvirus Is an Interaction Partner of Translation Initiation Factors eIF(iso)4E and eIF4E and Contains a 4E Binding Motif

“…In some virus-host combinations, simultaneous mutations in eIF(iso)4E and eIF4E are required to confer recessive resistance, e.g., resistance to Pepper veinal mottle virus and Chili veinal mottle virus in pepper (34,76), suggesting that these viruses may use both translation initiation factors for infection. Resistance conferred by the translation initiation factors can be overcome by amino acid changes in the VPg of TuMV, PVY, and TEV (5,14,26,37,57) but also the CI protein of LMV (1), the P3 protein of PSbMV (33), and the P1 protein of Clover yellow vein virus (58). The mechanisms by which the mutations in genes for translation initiation factors compromise virus infection and by which mutations in viral proteins overcome the resistance are not yet known.…”

Retos y oportunidades en la selección asistida de frijol resistente a BCMV y BCMNV en México. II. Oportunidades para la selección asistida

“…En muchos aislamientos potyvirales que rompen la resistencia de genes recesivos el determinante de virulencia es la VPg (Duprat et al, 2002;Charron, et al, 2008;Gallois, et al, 2010), y se sabe que muchas de las mutaciones de la VPg están localizadas en la región central involucrada en la interacción con eIF4E (Roudet-Tavert et al, 2007). Esto pone a la interacción entre la VPg y el eIF4E como un determinante clave de la virulencia o avirulencia en muchas, pero no en todas, las infecciones por potyvirus, ya que hay diversos casos reportados donde no encuentran interacción de la VPg con el eIF4E o su isoforma, aún en plantas susceptibles.…”

“…Esto pone a la interacción entre la VPg y el eIF4E como un determinante clave de la virulencia o avirulencia en muchas, pero no en todas, las infecciones por potyvirus, ya que hay diversos casos reportados donde no encuentran interacción de la VPg con el eIF4E o su isoforma, aún en plantas susceptibles. Un ejemplo es en chícharo con el gen sbm1 en su forma susceptible y el virus PSbMV (Gao et al, 2004), así como otros patosistemas entre eIF4Es y diversas VPg reconocidas como virulentas o aviruentas (Gallois et al, 2010).…”

“…In many potyvirus isolations that break recessive gene resistance the virulence factor is VPg (Duprat et al, 2002;Charron et al, 2008;Gallois et al, 2010), and it is known that many of VPg mutations are located in the central region involved in the interaction with eIF4E (Roudet-Tavert et al, 2007). This puts the interaction between VPg and eIF4E as por el virus, incluido el BCMV en frijol, es a través de la interacción directa con la proteína de unión al genoma viral o VPg (Figura 1).…”