Abstract
Extracellular vesicles, which carry bioactive cargos such as proteins, RNAs, and lipids, represent promising drug delivery vehicles owing to their biocompatibility, low immunogenicity, and inherent tissue-targeting capabilities. To address the current limitations in controlled cargo loading, we developed an abscisic acid (ABA)-inducible proximity system that directs proteins into exosomes during biogenesis. We engineered exosomal scaffolds by fusing the ABA receptor PYL1 to EV-enriched proteins-including BASP1, CD9, PTGFRN, and a truncated form PTGFRNΔ687-thereby creating docking sites within the exosomal lumen, while the target cargo (e.g., EGFP, firefly luciferase, or Cas9) was tagged with the ABI1 phosphatase domain. We demonstrate that ABA administration in producer cells induces PYL1-ABI1 complex formation, which recruits ABI1-fused cargo for selective encapsulation into EVs. Among the scaffolds tested, BASP1-PYL1 proved the most effective, enabling robust, ABA-dependent enrichment of cargo proteins. Purified EVs maintained canonical morphology, size, and marker expression (CD63, syntenin-1, CD9), confirming preserved biogenesis. Critically, these loaded exosomes efficiently delivered functional cargo to recipient cells, enabling Cas9/sgRNA-mediated genome editing. Together, our findings establish an ABA-triggered molecular switch for controllable EV protein loading, providing a versatile platform for next-generation therapeutic delivery.