Lipid droplets confer SA-dependent antiviral defense without growth penalty.

The role of lipid droplets (LDs), typically regarded as storage sites for neutral lipid, in plant defense remains poorly understood. In our study with barley stripe mosaic virus (BSMV), a (+)ssRNA virus, we found that infection significantly increases LD abundance in Nicotiana benthamiana and wheat. Using split-TurboID-based proximity labeling, we identified LD-associated proteins (LDAPs) at ER-chloroplast contact sites. Increasing LD formation by overexpressing mouse FIT2 or plant NbLDAP2.1 decreased viral accumulation, whereas impairing LD formation led to higher infection. Live cell imaging and genetic studies revealed that LDs move along actin filaments, cluster around chloroplasts, and contribute to antiviral immunity through a salicylic acid (SA)-dependent mechanism. Moreover, LDs conferred resistance to multiple (+)ssRNA viruses in N. benthamiana and a (-)ssRNA virus in rice. These findings uncover a role for LDs in SA-dependent antiviral defense that does not compromise growth, offering potential approaches for engineering virus-resistant crops.