Endogenous viral elements (EVEs) in Ectocarpus

Whether they can retain infective potential and contribute to active viral cycles has remained unresolved. Here, we demonstrate that EVEs in the brown alga Ectocarpus can reactivate and drive productive viral infections.

Using long-read sequencing and transcriptomics, we identify a full-length, transcriptionally active giant virus integrated within the host genome. Reactivation of this element is specific to reproductive cells, transforming gametangia into virus-producing structures, and viral symptoms strictly correlate to the presence of the active EVE. Genetic analyses show that the element is stably inherited, while its activation is precisely regulated by developmental and environmental cues.