Cytokinin arabinosides show increased efficacy in priming tomato immunity and inhibiting the fungal phytopathogen B. cinerea

Cytokinins (CKs) regulate numerous biological processes in plants, and are involved in plant growth and development as well as responses to biotic and abiotic stresses. Although CKs have been reported to prime plant immunity, thus far, research on CK hormopriming has focused on classical synthetic CKs such as kinetin or 6-benzylaminopurine (BAP). Here, we show that synthetic aromatic CK derivatives—specifically, 3‑methoxy-6-benzylaminopurine-9-arabinosides—effectively induce immune responses and promote resistance to Botrytis cinerea in tomato (Solanum lycopersicum) primarily via a salicylic acid (SA)-dependent mechanism. Additionally, like 6-BAP, these compounds directly inhibit B. cinerea. Transcriptomic analyses of B. cinerea treated with CK arabinosides revealed significant changes in expressed gene profiles, notably in pathways associated with sugar metabolism. Unlike classical CKs, CK arabinosides do not alleviate growth inhibition under sugar-limited conditions, contributing to their stronger antifungal effects. Furthermore, CK arabinosides induce tomato immune responses more robustly than classical CKs, yet without activating canonical cytokinin signaling pathways, likely owing to their exceptional chemical stability which prevents release of the free active CK base, and due to their inability to directly bind CK receptors. Altogether, our findings suggest that CK arabinosides act via a dual mechanism—immune priming and direct pathogen inhibition—and hold promise as next-generation hormopriming agents for sustainable crop protection.