Molecular choreography of vesicle trafficking: Exocyst-SNARE interplay in plant defense

The plant secretory system operates as a precision logistics network that sustains cellular homeostasis and mobilizes rapid defense against pathogens. Central to this system are SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins, which catalyze membrane fusion, and the octameric exocyst complex, which tethers trans-Golgi-derived vesicles to defined plasma-membrane domains. Rather than functioning independently, these machineries act as an interdependent module: the exocyst facilitates vesicle tethering and promotes SNARE complex assembly, while SNARE proteins reciprocally stabilize exocyst positioning and activity. This synergy ensures the targeted delivery of immune cargos-including pathogenesis-related proteins, callose synthases, transporters, and specialized metabolites-directly to pathogen attack sites. However, pathogens deploy effectors that disrupt exocyst-SNARE interfaces, weakening these defensive supply lines.

This review integrates recent advances that expand the functional repertoire of both complexes across canonical and unconventional secretion pathways. It incorporates regulatory factors such as Rab GTPases, Rho-GTPases of plants (ROPs), phosphoinositides, cytoskeletal elements, and post-translational modifications, offering a comprehensive framework for understanding exocyst-SNARE coordination in plant defense. At the same time, it highlights key unresolved questions, such as the molecular choreography of holo-exocyst-SNARE assemblies in vivo, rules of immune cargo selection, and the dynamic rerouting of pathways during stress.

A central theme emerging from these insights is the cooperative interaction between exocyst and SNARE proteins as the basis for localized immune delivery. However, the vulnerability of this machinery to pathogen interference underscores the need for deeper mechanistic understanding. This review positions vesicle-fusion control as a promising and tractable strategy for engineering durable disease resistance in crops, framing exocyst-SNARE biology as a critical lever in strengthening plant immunity.