Salicylic Acid Engages Central Metabolic Regulators SnRK1 and TOR to Govern Immunity by Differential Phosphorylation of NPR1

Abstract

Immunity is a delicate balance between combating infection and preserving the metabolic functions vital for host survival. However, the mechanisms by which immune responses are coordinated with cellular metabolism remain largely unknown. Here, we show that NONEXPRESSER OF PR GENES 1 (NPR1), the central plant immune regulator of salicylic acid (SA)-mediated defense responses, is controlled by a cascade of posttranslational modifications (PTMs) involving two master nutrient-sensing kinases. Under normal growth conditions, TARGET OF RAPAMYCIN (TOR) inhibits NPR1 through phosphorylation at Ser-55/59. During defense responses, elevated SA enhances SNF1-RELATED KINASE 1 (SnRK1) activity, which in turn inhibits TOR signaling and phosphorylates NPR1 at Ser-557. This phosphorylation event activates NPR1 and facilitates its subsequent PTMs. Together, our results reveal an integral role of SA (the active metabolite of aspirin) in controlling central metabolic regulators SnRK1 and TOR to coordinate immune responses and growth through antagonistic modifications of NPR1.