Pipecolic acid: A positive regulator of systemic acquired resistance and plant immunity

• Published in: Biochimica et biophysica acta. General subjects Vol. 1869; no. 7; p. 130808
• Main Authors: Kumari, Megha, Sharma, Prashansa, Singh, Archana
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.06.2025
• Subjects: autophagy; biosynthesis; Disease Resistance; flavin-containing monooxygenase; immunity; lysine; NHP; ornithine; pathogens; phloem; Pip; pipecolic acid; Pipecolic Acids - immunology; Pipecolic Acids - metabolism; Plant defense; Plant Diseases - immunology; Plant Immunity; Plants - immunology; Plants - metabolism; salicylic acid; SAR; symplast; systemic acquired resistance; Plant defense; SAR; Pip; SA; NHP
• ISSN: 0304-4165; 1872-8006; 1872-8006
• DOI: 10.1016/j.bbagen.2025.130808

Pipecolic acid (Pip) is a naturally occurring non-protein amino acid, that builds up in plants in response to pathogen infection. Pip is upregulated in autophagy mutants, indicating its role as a crucial regulator of plant immunity by upregulating systemic acquired resistance (SAR). This broad-spectrum defense mechanism protects uninfected parts of the plant during subsequent pathogen attacks. Pip has been identified as a SAR chemical signal and acts before the NO-ROS-AzA-G3P. The biosynthesis of Pip begins with lysine by the activity of ALD1 and SARD4 in a sequential manner; ALD1, a lysine aminotransferase, catabolizes lysine to Δ 1-piperidine-2-carboxylic acid, which is further modified to Pip by the activity of ornithine cyclodeaminase activity of SARD4. Additionally, FMO 1, a flavin monooxygenase, catalyzes the synthesis of N-hydroxy-pipecolic acid (NHP, the final, SAR-inducing defense hormone) from Pip. Pip and its active form accumulate at the infection site in the phloem and are transported to distal parts of the plant via symplast to trigger SAR. This review focuses on the roles of Pip and NHP in regulating SAR and how they interact with other defense signals like salicylic acid (SA) to modulate plant immunity. •Pip is a non-protein amino acid that activates SAR.•Pip is synthesized from lysine through a sequential process involving ALD1, SARD4 and FMO.•Pip acts upstream of the NO-ROS-AzA-G3P branch of the SAR pathway.•Pip accumulates in the phloem and is transported to distal regions via the symplast to induce SAR.•NHP is the bioactive form of Pip and act as an important molecule in modulating SAR.