Tobacco etch virus Infectivity in Capsicum Spp. Is Determined by a Maximum of Three Amino Acids in the Viral Virulence Determinant VPg

Abstract

Potyvirus resistance in Capsicum spp. has been attributed to amino acid substitutions at the pvr1 locus that cause conformational shifts in eukaryotic translation initiation factor eIF4E. The viral genome-linked protein (VPg) sequence was isolated and compared from three Tobacco etch virus (TEV) strains, highly aphid-transmissible (HAT), Mex21, and N, which differentially infect Capsicum genotypes encoding Pvr1(+), pvr1, and pvr1(2). Viral chimeras were synthesized using the TEV-HAT genome, replacing HAT VPg with Mex21 or N VPg. TEV HAT did not infect pepper plants homozygous for either the pvr1 or pvr1(2) allele. However, the novel chimeric TEV strains, TEVHAT(Mex21-VPg) and TEV-HAT(N-VPg), infected pvr1 and pvr1(2) pepper plants, respectively, demonstrating that VPg is the virulence determinant in this pathosystem. Three dimensional structural models predicted interaction between VPg and the susceptible eIF4E genotype in every case, while resistant genotypes were never predicted to interact. To determine whether there is a correlation between physical interaction of VPg with eIF4E and infectivity, the effects of amino acid variation within VPg were assessed. Interaction between pvr1(2) eIF4E and N VPg was detected in planta, implying that the six amino acid differences in N VPg relative to HAT VPg are responsible for restoring the physical interaction and infectivity.

3′ Cap-Independent Translation Enhancers of Plant Viruses

“…Recessive resistance to potyviruses, which have a 5′ VPg, an IRES in the 5′ UTR, and 3′ poly(A) tails, has long been known to map to specific, incompatible eIF4E isoforms (48). These isoforms retain 5′ cap–binding activity but cannot engage in a required, but functionally undefined, direct interaction with the potyviral 5′ VPg (32, 42). Of the 14 known recessive resistance genes, 12 map to eIF4E or its functionally redundant isoform, eIFiso4E, with the remainder mapping to eIF4G or its isoform, eIFiso4G (60).…”

A Tobacco etch virus NW isolate that overcomes pvr1 and pvr12 resistance in Capsicum sp.

“…The present report most closely aligns with the work of Perez et al . (); for this reason, the sequence analysis focused on the VPg of the NW isolates.…”

“…The key amino acid residue identified as the virulence determinant for TEV‐Mex21 in CA4 and TEV‐N in Dempsey was residue 113 (Perez et al ., ). A L113 is favourable for infection of CA4 plants by TEV‐Mex21 and a H113 favours infection of Dempsey plants by TEV‐N.…”

“…The central region of the VPg of PVY was shown to be responsible for that virus’ ability to overcome pot1 and pvr1 2 resistance genes in tomato and pepper, respectively (Moury et al ., ). Chimeric TEV strains consisting of exchanged VPg coding regions demonstrated that the VPg alone was responsible for overcoming CA4 and Dempsey resistances (Perez et al ., ). The present report most closely aligns with the work of Perez et al .…”

“…The potyviral VPg was shown to be a virulence determinant (Leonard et al, 2000;Moury et al, 2004;Ayme et al, 2006Ayme et al, , 2007Gallois et al, 2010;Perez et al, 2012) and, for some virus-host interactions, one or more amino acids in the central region of the viral VPg were identified that enabled the virus to overcome resistance, e.g. in pepper, different PVY strains and resistance alleles pvr1 1 , pvr1 2 and pvr1 3 (Moury et al, 2004;Ayme et al, 2006Ayme et al, , 2007 and TEV strains and resistance alleles pvr1 and pvr1 2 (Perez et al, 2012). The potential for a virus species to overcome these resistance alleles represents a serious threat to the pepper industry.…”