Mapping of viral genomic regions important in cross-protection between strains of a potyvirus.
Cross-protection was tested between potato and tobacco strains of Potato virus A, a member of the genus Potyvirus (PVA), in tobacco plants. Cross-protection was effective only at the initiation of infection. The potato strains provided only weak cross-protection against the tobacco strain, whereas the tobacco strain provided strong cross-protection against potato strains. The tamarillo strain (TamMV) showed cross-protection phenotypes mostly resembling those of the potato strains. Chimera of the PVA strains were utilized to map viral genomic regions important for cross-protection. The coat protein (CP) encoding region and the helper component proteinase (HCpro) affected cross-protection and virus accumulation. An amino acid substitution at the CP N-terminus reduced virus accumulation and the ability to overcome cross-protection, whereas amino acid substitutions introduced to the HCpro increased virus accumulation and the ability to overcome cross-protection. Closer sequence relatedness between the protector and challenger isolate, as determined by the CP-encoding sequence, was correlated with an increased cross-protection ability. Cross-protection was not overcome by inoculation with nonencapsidated viral RNA. Thus, the differences in cross-protection abilities between PVA strains and chimera were not explained with the "re-encapsidation model" described for strains of Tobacco mosaic tobamovirus but may be associated with a virus infection-induced RNA silencing mechanism.
Department of Plant Biology, Genetics Centre, SLU, Uppsala, Sweden. jari.valkonen@vbiol.slu.se
Jari P T
JP
Valkonen
Minna-Lilsa
ML
Rajamäki
Tuija
T
Kekarainen
D000914:Antibodies, Viral / Q000276:immunology; D016679:Genome, Viral; D017800:Potyvirus / Q000235:genetics* / Q000276:immunology / Q000302:isolation & purification; D012367:RNA, Viral / Q000235:genetics / Q000502:physiology; D011198:Solanum tuberosum / Q000821:virology; D013045:Species Specificity; D014026:Nicotiana / Q000821:virology; D014765:Viral Vaccines
D000914:Antibodies, Viral; D012367:RNA, Viral; D014765:Viral Vaccines