P3 and NIa-Pro of turnip mosaic virus are independent elicitors of superinfection exclusion

Authors: NUNNA, HARITHA - University Of Nebraska; QU, FENG - The Ohio State University; Tatineni, Satyanarayana - Ts

Submitted to: Viruses
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2023
Publication Date: 6/28/2023
Citation: Nunna, H., Qu, F., Tatineni, S. 2023. P3 and NIa-Pro of turnip mosaic virus are independent elicitors of superinfection exclusion. Viruses. https://doi.org/10.3390/v15071459.
DOI: https://doi.org/10.3390/v15071459

Interpretive Summary: Superinfection exclusion (SIE) is a poorly understood phenomenon where plant infection with one virus prevents infection by a closely related second virus. Turnip mosaic virus (TuMV) is an economically important virus infecting the cabbage family of crops. The ability of TuMV to infect the experimental plant Nicotiana benthamiana allows researchers to determine the mechanism responsible for SIE. In this study, the genes of TuMV were screened to determine which ones are involved in SIE. The protein from two genes, but not the RNA sequence were shown to be required for SIE. This research laid the foundation for further investigations and the development of new strategies to control viruses using SIE. The mechanistic studies on SIE using TuMV are applicable to wheat streak mosaic virus and Triticum mosaic virus, which are economically destructive viral pathogens to wheat in the Great Plains.

Technical Abstract: Superinfection exclusion (SIE) is an antagonistic interaction between identical or closely related viruses in host cells. Previous studies by us and others led to the hypothesis that SIE was elicited by one or more proteins encoded in the genomes of primary viruses. Here we tested this hypothesis using Turnip mosaic virus (TuMV), a member of the genus Potyvirus of the family Potyviridae with significant economic consequences. To this end, individual TuMV-encoded proteins were transiently expressed in the cells of Nicotiana benthamiana leaves, followed by challenged with a modified TuMV expressing the green fluorescent protein (TuMV-GFP). Three days after TuMV-GFP delivery, these cells were examined for replication-dependent expression of GFP. Cells expressing TuMV P1, HC-Pro, 6K1, CI, 6K2, NIa-VPg, NIb, or CP proteins permitted efficient expression of GFP, suggesting that these proteins failed to block the replication of a superinfecting TuMV-GFP. By contrast, N. benthamiana cells expressing TuMV P3 or NIa-Pro did not express visible GFP fluorescence, suggesting that both of them could elicit potent SIE against TuMV-GFP. The SIE elicitor activity of P3 and NIa-Pro were further confirmed by their heterologous expression from a different potyvirus, potato virus A (PVA). Plants systemically infected with PVA variants expressing TuMV P3 or NIa-Pro blocked subsequent infection by TuMV-GFP. A +1-frameshift mutation in P3 and NIa-Pro cistrons facilitated superinfection by TuMV-GFP, suggesting that the P3 and NIa-Pro proteins but not the RNA are involved in SIE activity. Additionally, deletion mutagenesis identified P3 amino acids 3-200 of 352 and NIa-Pro amino acids 3-40 and 181-242 of 242 as essential for SIE elicitation. Collectively, our study demonstrates that TuMV encodes two spatially separated proteins that act independently to exert SIE to superinfecting TuMV. These results lay the foundation for further mechanistic interrogations of SIE in this virus.