A Geminivirus Betasatellite Subverts the Viral Coat Protein-Mediated Resistance to Promote Systemic Infection

Viral coat protein (CP)-mediated resistance represents an effective strategy that confers robust antiviral defense in plants. However, the functional relevance of this resistance mechanism during mixed infections by distinct viral species remains largely elusive. Mixed viral infections in agricultural crops frequently lead to exacerbated disease symptoms and substantial yield losses, posing a severe threat to global agricultural production. In this study, we demonstrate that expression of tomato leaf curl New Delhi virus (ToLCNDV) CP confers effective resistance against tomato yellow leaf curl China virus (TYLCCNV), another prominent geminivirus. Strikingly, the βC1 protein encoded by TYLCCNV betasatellite can fully counteract this CP-mediated resistance through direct interaction with ToLCNDV CP and promotion of its proteasome-dependent degradation. We further identified the residue Tyr110 of βC1 as essential for the interaction and subsequent CP degradation. Consequently, βC1-mediated suppression of CP resistance promotes efficient systemic infection of ToLCNDV DNA A. Collectively, our results uncover a novel mechanism by which a viral effector antagonizes viral CP-mediated host resistance during mixed viral infections, offering important insights into viral pathogenesis and the development of sustainable disease control strategies.