Limited Specificity of GroEL-Homolog Interactions with Plant Virus Coat Proteins Challenges Models of Vector-Mediated Virus Transmission

Plant viruses often depend on insect vectors for transmission, and interactions between viral coat proteins (CP) and insect endosymbiont-derived chaperonins may facilitate viral persistence within the vector. This study investigated interactions between a GroEL-homolog protein (GroHp) produced by the beet leafhopper endosymbiont Sulcia muelleri (SMBLH GroHp) and several plant virus CPs. Using PCR-capture assays, ELISA, and bacterial two-hybrid assays, we evaluated binding between SMBLH GroHp and multiple plant viruses and compared these interactions with those of Escherichia coli GroEL. Contrary to expectations, SMBLH GroHp did not exhibit strong specificity toward curtovirus CPs and showed weak interactions across multiple viral proteins, while GroEL displayed stronger and broader binding. Structural and biochemical characteristics of CPs, including charge and isoelectric point, were insufficient to predict binding affinity, suggesting additional molecular determinants influence GroHp-CP interactions. Furthermore, GroHp abundance did not differ between viruliferous and aviruliferous insects, indicating that GroHp is constitutively expressed and not induced by viral presence. These findings suggest that GroHp-CP interactions alone are unlikely to fully determine vector specificity or transmission efficiency. Instead, viral transmission likely depends on combined factors involving viral properties, vector physiology, and potentially additional molecular interactions within the vector.