A tobamovirus RNA motif and TMV-Hel cooperatively suppress the host defense factor TRX

Abstract Viruses encode a limited number of proteins and often expropriate host factors for their successful infection and propagation. The molecular composition of the complex used for synthesis of the viral subgenomic (sg) RNAs remains largely unknown. In this study, an RNA motif (45 nt), equivalent to the sequence coding for the N-terminal portion of the tobamovirus coat protein (CP), known to be an enhancer-like element (tentatively designated as EL1) of the CP sg promoter, was used as a bait to capture bound proteins. Nicotiana benthamiana thioredoxin h-type 1 (NbTRXh1), a host defense factor with redox activity, was identified and its enzymatic active site was determined to be covered by EL1, thus blocking its reductase activity. In addition, the virus replicase Hel domain interacted with NbTRXh1, resulting in a decrease in NbTRXh1 protein accumulation in N. benthamiana. Thus, the viral RNA element and viral protein integrated their suppression of NbTRXh1 to facilitate viral CP sgRNA synthesis. Understanding this multiplexed regulatory mechanism between tobamovirus EL1 and associated proteins will assist in designing strategies for virus resistance and for optimization of the production of exogenous proteins under the control of the viral sg promoter.