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

¹Department of Plant Breeding and Genetics, Cornell University, Ithaca, NY 14853 U.S.A.; ²Department of Horticulture and Breeding, Andong National University, Andongsi, Gyeongsangbukdo, 760-749, Republic of Korea; ³Department of Plant Science, College of Agriculture and Life Sciences, Seoul National University, Seoul 151-742, Republic of Korea; ⁴Computational Biology Service Unit, Life Sciences Core Laboratories Center, Cornell University, Ithaca, NY 14853 U.S.A.; ⁵Department of Entomology & Plant Pathology, Auburn University, AL 36849-5409, U.S.A.; ⁶Laboratory of Genetics and Department of Agronomy, University of Wisconsin-Madison, Madison 53706 U.S.A.

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 pvr1². 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 pvr1² allele. However, the novel chimeric TEV strains, TEV-HAT^Mex21-VPg and TEV-HAT^N-VPg, infected pvr1 and pvr1² 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 pvr1² 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.