Pipecolic acid (Pip), a non-proteinaceous product of lysine catabolism, is an important regulator of immunity in plants and humans alike. In plants, Pip accumulates upon pathogen infection and has been associated with systemic acquired resistance (SAR). However, the molecular mechanisms underlying Pip-mediated signaling and its relationship to other known SAR inducers remain unknown. We show that in plants, Pip confers SAR by increasing levels of the free radicals, nitric oxide (NO), and reactive oxygen species (ROS), which act upstream of glycerol-3-phosphate (G3P). Plants defective in NO, ROS, G3P, or salicylic acid (SA) biosynthesis accumulate reduced Pip in their distal uninfected tissues although they contain wild-type-like levels of Pip in their infected leaves. These data indicate that de novo synthesis of Pip in distal tissues is dependent on both SA and G3P and that distal levels of SA and G3P play an important role in SAR. These results also suggest a unique scenario whereby metabolites in a signaling cascade can stimulate each other's biosynthesis depending on their relative levels and their site of action.
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This work was supported by grants from the NSF (MCB#0421914, #1243849, and IOS#051909), the Kentucky Science and Engineering Foundation (#1244), the Kentucky Soybean Board (3084113467), and the Kentucky Tobacco Research and Development Center.
All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors.
Wang, Caixia; Liu, Ruiying; Lim, Gah-Hyun; de Lorenzo, Laura; Yu, Keshun; Zhang, Kai; Hunt, Arthur G.; Kachroo, Aardra; and Kachroo, Pradeep, "Pipecolic Acid Confers Systemic Immunity by Regulating Free Radicals" (2018). Plant Pathology Faculty Publications. 78.