NbHDR, A Host Protein Involved in the MEP Pathway, Interacts With Bamboo Mosaic Virus Replicase and Enhances Viral Accumulation.

Abstract

Plant viruses, as obligate parasites, depend on host cellular machinery for various processes essential to their life cycle, making the investigation of these interactions fundamentally important. Bamboo mosaic virus (BaMV), a positive-strand (+) RNA virus, serves as a model to explore host-virus interactions during replication. In this study, Nicotiana benthamiana 1-hydroxy-2-methyl-butenyl 4-diphosphate reductase (NbHDR), a key enzyme in the methylerythritol 4-phosphate (MEP) pathway, was identified as an interactor with BaMV replicase through immunoprecipitation, pull-down and yeast two-hybrid assays. Knockdown of NbHDR significantly reduced the accumulation of BaMV RNA and coat protein but did not affect infection with the close relative potato virus X, indicating its specific involvement in BaMV replication. Overexpression of NbHDR in N. benthamiana or the addition of NbHDR in in vitro RdRp reactions demonstrated that NbHDR enhances BaMV replication by promoting (+) RNA synthesis. To further explore whether the role of NbHDR in BaMV replication is linked to gibberellic acid (GA) synthesis through the MEP pathway, individual knockdowns of NbHDR and ent-kaurene synthase (KS), a key enzyme in GA biosynthesis, were performed. Silencing KS sireduced BaMV accumulation, which was rescued by exogenous GA, but GA supplementation was insufficient to restore BaMV levels after NbHDR silencing. These findings suggest that NbHDR associates with the BaMV replication complex to enhance viral replication efficiency through a mechanism independent of GA synthesis from the MEP pathway, providing new insights into host-virus interactions.