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Poster: Molecular & Cellular Plant-Microbe Interactions: Biochemistry & Cell Biology


Wheat streak mosaic virus-encoded NIa-Pro and coat protein are involved in virus superinfection exclusion

Cross protection or superinfection exclusion (SE) is defined as the phenomenon whereby initial infection by one virus prevents subsequent infection by closely related viruses. The mechanisms of SE are just beginning to be understood. Wheat streak mosaic virus (WSMV; genus: Tritimovirus; family: Potyviridae) is an economically important wheat virus. Proteins encoded by WSMV were individually expressed in wheat using an unrelated Triticum mosaic virus (TriMV) gene expression vector, followed by challenge inoculation with GFP-tagged WSMV (WSMV-GFP). Wheat plants infected with TriMV expressing WSMV P1, HC-Pro, P3, 6K1, CI, 6K2, NIa-VPg or NIb cistrons did not prevent superinfection by WSMV-GFP. However, expression of WSMV NIa-Pro or CP greatly reduced superinfection by WSMV-GFP, suggesting that NIa-Pro and CP are involved in SE. Expression of WSMV NIa-Pro or CP cistron with frameshift mutations did not exhibit SE against WSMV-GFP, indicating that the NIa-Pro and CP proteins but not the RNA sequences are involved in SE. A series of deletions comprising 60 amino acid (aa) sets covering the entire NIa-Pro cistron revealed that the complete NIa-Pro protein is required for SE activity. In contrast, WSMV CP aa 3-100 and 301-349 were dispensable for SE but not aa 101-300. Expression of WSMV CP aa 101 to 300 in TriMV exhibited the same SE activity as full-length CP. In reciprocal experiments, wheat infected with WSMV expressing TriMV CP prevented superinfection by TriMV-GFP.