Plants Pack a Quiver Full of Arrows Pradeep Kachroo, Aardra Kachroo  Cell Host & Microbe  Volume 23, Issue 5, Pages 573-575 (May 2018) DOI: 10.1016/j.chom.2018.04.014 Copyright © 2018 Elsevier Inc. Terms and Conditions

Figure 1 A Simplified Model Illustrating the Enzymatic Steps Leading to NHP Biosynthesis and the Relationship between Pip- and G3P-Induced SAR Signaling Pathogen infection triggers ALD1-mediated conversion of lysine (Lys) to the Δ1-piperideine-2 carboxylic acid (P2C) intermediate, which is then coverted to pipecolic acid (Pip) in a reaction catalyzed by SARD4 and other unknown enzymes (indicated by ?). Pip is hydroxylated to form N-hydroxypipecolic acid (NHP), which undergoes glycosylation to form the NHP glucoside conjugate NOGP (abbreviated as N-OGlc-Pip elsewhere). Whether N-OGlc-Pip is a storage or biologically active derivative of NHP is not known. Pip-mediated SAR is dependent on the NO-ROS-AzA-G3P branch of the SAR pathway and activates SAR by inducing ROS accumulation. Based on the known involvement of FMOs in ROS production, it is possible that the FMO1-catalyzed step contributes to ROS biosynthesis. ROS and NO operate in a feedback loop to confer SAR. Pip, NHP, AzA, and G3P are all transported from the infected to uninfected tissues (red lines and arrows). All enzymes are highlighted in green, products derived from Lys in blue, and chemicals involved in the nitric oxide (NO)-reactive oxygen species (ROS)-azelaic acid (AzA)-glycerol-3-phosphate (G3P) branch in yellow. Cell Host & Microbe 2018 23, 573-575DOI: (10.1016/j.chom.2018.04.014) Copyright © 2018 Elsevier Inc. Terms and Conditions