A viral protease relocalizes in the presence of the vector to promote vector performance.

Vector-borne pathogens influence host characteristics relevant to host-vector contact, increasing pathogen transmission and survival. Previously, we demonstrated that infection with Turnip mosaic virus, a member of one of the largest families of plant-infecting viruses, increases vector attraction and reproduction on infected hosts. These changes were due to a single viral protein, NIa-Pro. Here we show that NIa-Pro responds to the presence of the aphid vector during infection by relocalizing to the vacuole. Remarkably, vacuolar localization is required for NIa-Pro's ability to enhance aphid reproduction on host plants, vacuole localization disappears when aphids are removed, and this phenomenon occurs for another potyvirus, Potato virus Y, suggesting a conserved role for the protein in vector-host interactions. Taken together, these results suggest that potyviruses dynamically respond to the presence of their vectors, promoting insect performance and transmission only when needed.