Submitted to: Virology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/17/2004
Publication Date: 6/1/2004
Citation: Stenger, D.C., French, R.C. 2004. Functional replacement of wheat streak mosaic virus hc-pro with the corresponding cistron from a diverse array of viruses in the family potyviridae. Virology 323:257-267. Interpretive Summary: The HC-Pro gene of wheat streak mosaic virus strain Sidney 81(WSMV-S81) was systematically replaced with the corresponding gene from other viruses. The resulting viruses were tested for infectivity in wheat, oat and corn. HC-Pro genes derived from different strains of WSMV and from the closely related oat necrotic mottle virus were capable of infecting wheat, oat, and corn. These results indicated that differences in host range between WSMV-S81 and other WSMV strains or oat necrotic mottle virus are not determined by the HC-Pro gene. In contrast, HC-Pro genes derived from distantly related rymoviruses and potyviruses resulted in a restriction of host range in which wheat but not oat or corn could be infected. These results suggest that virus-host interactions required for WSMV infection of oat and corn are more stringent than for wheat. Differences in symptom severity and mechanical inoculation efficiency of certain HC-pro gene replacements further suggest that HC-Pro may play a role in disease severity and fitness.
Technical Abstract: HC-Pro of Wheat streak mosaic virus strain Sidney 81 (WSMV-Sidney 81) was systematically replaced with the corresponding cistron derived from four strains of WSMV (Type, TK1, CZ, and El Batán 3), the tritimovirus Oat necrotic mottle virus (ONMV), the rymoviruses Agropyron mosaic virus (AgMV) and Hordeum mosaic virus (HoMV), or the potyviruses Tobacco etch virus (TEV) and Turnip mosaic virus (TuMV). These HC-Pro proteins varied in amino acid sequence identity shared with HC-Pro of WSMV-Sidney 81 from high (strains of WSMV at ~86-99%), to moderate (ONMV at 70%) to low (rymoviruses and potyviruses at ~15-17%). Surprisingly, all chimeric viral genomes examined were capable of systemic infection of wheat upon inoculation with RNA transcripts produced in vitro. HC-Pro replacements derived from tritimoviruses did not alter host range relative to WSMV-Sidney 81, as each of these chimeric viruses were able to systemically infect wheat, oat, and corn line SDp2. These results indicate that differences in host range among tritimoviruses, including the inability of ONMV to infect wheat or the inability of WSMV strains Type and El Batán 3 to infect SDp2 corn, are not determined by HC-Pro. In contrast, all chimeric viruses bearing HC-Pro replacements derived from rymoviruses or potyviruses were unable to infect SDp2 corn and oat. Collectively, these results indicate that HC-Pro from distantly related virus species of the family Potyviridae are competent to provide WSMV-Sidney 81 with all functions necessary for infection of a permissive host (wheat) and that virus-host interactions required for systemic infection of oat and SDp2 corn are more stringent. Changes in symptom severity or mechanical transmission efficiency observed for some chimeric viruses further suggests that HC-Pro affects virulence in WSMV.