A plant virus causes symptoms through the deployment of a host-mimicking protein domain to attract the insect vector

Plant viruses cause symptoms with devastating consequences for agriculture. However, the molecular mechanisms underlying symptom development in viral infections remain largely unexplored. Here, we show that tomato yellow leaf curl virus (TYLCV) interferes with host developmental programs through a host-mimicking domain present in the viral C4 protein. This domain mediates the interaction between C4 and a family of RCC1-like domain-containing (RLD) proteins, previously shown to be required for proper plant development and environmental responses. C4 outcompetes an endogenous interactor of RLDs, hijacking RLD proteins to the plasma membrane and disrupting their function in orchestrating endomembrane trafficking and polar auxin transport. Strikingly, macroscopic symptoms do not affect viral accumulation in the plant but serve as attractants for the insect vector, presumably promoting pathogen spread in an ecological context. Our work sheds light on the molecular underpinnings and biological relevance of symptom development triggered by TYLCV in tomato. Since most plant viruses are insect-transmitted, the principles described here might have broad applicability to crop-virus interactions.