Arabidopsis UGT76B1 glycosylates N-hydroxy-pipecolic acid and inactivates systemic acquired resistance in tomato.

Systemic acquired resistance (SAR) is a mechanism that plants utilize to connect a local pathogen infection to global defense responses. N-hydroxy-pipecolic acid (NHP) and a glycosylated derivative are produced during SAR, yet their individual roles in this process are currently unclear. Here, we report that Arabidopsis thaliana UGT76B1 generated glycosylated NHP (NHP-Glc) in vitro and when transiently expressed alongside Arabidopsis NHP biosynthetic genes in two Solanaceous plants. During infection, Arabidopsis ugt76b1 mutants did not accumulate NHP-Glc and accumulated less glycosylated salicylic acid (SA-Glc) than wild-type plants. The metabolic changes in ugt76b1 plants were accompanied by enhanced defense to the bacterial pathogen Pseudomonas syringae, suggesting that glycosylation of the SAR molecules NHP and salicylic acid by UGT76B1 plays an important role in modulating defense responses. Transient expression of Arabidopsis UGT76B1 with the Arabidopsis NHP biosynthesis genes ALD1 and FMO1 in tomato (Solanum lycopersicum) increased NHP-Glc production and reduced NHP accumulation in local tissue and abolished the systemic resistance seen when expressing NHP-biosynthetic genes alone. These findings reveal that the glycosylation of NHP by UGT76B1 alters defense priming in systemic tissue and provide further evidence for the role of the NHP aglycone as the active metabolite in SAR signaling.