AGD2-like DEFENSE RESPONSE PROTEIN 1 (ALD1) is an aminotransferase that is necessary for the biosynthesis of the immune-active non-protein amino acid pipecolic acid (Pip). Pip and its N-hydroxylated derivative, N-hydroxy-Pip (NHP), have been suggested as possible long-distance signals moving in plants from infected to systemic, uninfected sites to enhance immunity. Jiang et al. (2021) show that accumulation of ALD1 in epidermal chloroplasts at local, infected sites promotes systemic immunity. Their results highlight the epidermis as a site of active immune signaling and ALD1 as an important upstream regulator of long-distance signal transmission in systemic acquired resistance (SAR).