Functional Dissection of the Turnip Crinkle Virus Coat Protein Links ATG8 Association to Autophagy-Associated Antiviral Regulation.

The coat protein (CP) of turnip crinkle virus (TCV) plays multifaceted roles in viral infection, acting as both an avirulence (Avr) factor recognized by the resistance protein HRT and a viral suppressor of RNA silencing (VSR). However, how these dual activities are coordinated remains unclear. Here, we demonstrate that the position of a fluorescent protein (FP) tag on CP functionally separates its two activities. C-terminal tagging (CP-GFP) preserved the ability to trigger HRT-dependent hypersensitive response (HR) but abolished silencing suppression, whereas N-terminal tagging (YFP-CP) retained VSR activity but failed to induce HR. These functional differences correlated with distinct subcellular localizations: Avr activity required both nuclear and cytoplasmic localization, while VSR function was confined to the cytoplasm. We further show that the N-terminal region of CP associates with autophagy-related protein 8 (ATG8), linking CP to autophagy-associated antiviral pathways. Autophagy-deficient atg5 and atg7 mutants exhibited enhanced susceptibility to TCV, supporting a role for autophagy in antiviral defence during infection. Together, our findings reveal that TCV CP contains spatially and mechanistically separable determinants for Avr and VSR functions and identify CP-ATG8 association as a potential interface between viral infection and host autophagy-associated regulation.