Molecular Characterization of Tobacco Necrosis Virus A Variants Identified in Sugarbeet Roots

Sugarbeet provides an important source of sucrose, a stable, environmentally safe, and low-cost staple in the human diet. Viral diseases arising in sugarbeet ultimately impact sugar content, which translates to financial losses for growers. To manage diseases and prevent such losses from occurring, it is essential to characterize viruses responsible for disease. Recently, our laboratory identified a tobacco necrosis virus A variant named Beta vulgaris alphanecrovirus-1 (BvANV-1) in sugarbeet roots. We validated the infectivity of BvANV-1 using two DNA-based clones: one sequence referred to as the wild type and another as mutant #7 that harbors one nonsynonymous and one synonymous mutation in the viral replicase gene (p23) and one synonymous mutation in the p8 movement protein gene relative to the wild type. The host range of the virus was determined through inoculating a series of local weed species and agriculturally relevant hosts, which showed that soybean and pinto bean are potentially important hosts of this virus. Using both clones, viral transmission to sugarbeet by Olpidium virulentus was verified. Using site-directed mutagenesis of mutant #7, we demonstrated that the amino acid change in the p23 gene alone restored the phenotype similar to the wild type on Nicotiana benthamiana-inoculated leaves. Additionally, this latter change and the synonymous mutation in the p8 gene were both required to re-establish systemic infection in N. benthamiana similar to the wild type. Our analysis reveals differences among both variants and lays the groundwork for characterizing the role of BvANV-1 proteins during infection. [Formula: see text] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.