Far-red light orchestrates antiviral defense in plants.

Light undergoes dramatic spectral shifts at dusk (sunset) and dawn (sunrise), enhancing insect activity and increasing the risk of insect-borne virus transmission. However, how plants respond to these light changes and associated viral threats remains unclear. Here, we show that far-red (FR) light, enriched in skylight during dusk and dawn, activates plant antiviral defense via phytochrome A (phyA). FR light-induced phyA activation promotes degradation of phytochrome interacting factor 1 (PIF1), which triggers the REVEILLE 7 (RVE7)-enhanced disease susceptibility 1 (EDS1) cascade to enhance salicylic acid (SA) signaling. Furthermore, multiple viruses use their RNA-dependent RNA polymerases to disrupt the phyA-far-red elongated hypocotyl 1 (FHY1) interaction to block phyA nuclear transport, impairing FR light-induced plant defense. Our findings uncover the molecular basis of FR light-mediated plant antiviral defense and reveal a previously unidentified viral counter-defense mechanism, highlighting how plants interpret environmental light cues to adapt to insect-borne viral infections.