Identification of critical interaction sites in the coat protein of Areca palm velarivirus 1 (APV1) and its pathogenicity

Abstract Areca palm velarivirus 1 (APV1), a member of the genus Velarivirus (family Closteroviridae ), is an economically significant pathogen associated with yellow leaf disease in Areca palm ( Areca catechu L.), causing substantial declines in both yield and quality decline. The APV1 genome comprises 11 open reading frames (ORFs), with ORF6 and ORF7 encoding the coat protein (CP) and minor coat protein (CPm), respectively. In this study, the interaction between the APV1 CP and CPm proteins was identified by yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays. To clarify critical interaction sites, a double mutant (CP R211A−R212A ) was generated through site-directed mutagenesis for both Y2H and BiFC analyses. The result demonstrated that these residues were determined to be key amino acid sites. Furthermore, subcellular localization analysis revealed that the CP R211A−R212A mutation did not alter the functional localization of the CP protein in Nicotiana benthamiana leaves, as it remained present in both the nucleus and cytoplasm. The pathogenicity of the APV1 CP protein and its mutant was investigated using the potato virus X (PVX) expression system. Experimental results showed that N. benthamiana plants infected with PVX-CP exhibited severe chlorosis symptoms. Intriguingly, N. benthamiana plants infected with PVX-CP R211A−R212A showed markedly reduced chlorosis. Our findings indicated that the 211 RR 212 residues of APV1 CP are crucial for their interaction with the CPm protein and likely play a key role in the symptom formation. Moreover, this study represents the first identification of APV1 CP as a pathogenic factor, offering new insights into the molecular mechanisms underlying APV1 pathogenicity.