N-hydroxypipecolic acid primes plants for enhanced microbial pattern-induced responses

Area of Science:

• Plant immunity
• Molecular plant-pathogen interactions
• Plant biochemistry

Background:

• Flagellin, a bacterial elicitor, triggers plant immune responses, but these are often moderate.
• Systemic acquired resistance (SAR) is a plant defense mechanism induced by pathogens.
• N-hydroxypipecolic acid (NHP) is known to induce SAR.

Purpose of the Study:

• To investigate how NHP primes Arabidopsis thaliana plants for enhanced responses to flagellin elicitor flg22.
• To elucidate the interplay between NHP, salicylic acid (SA), and plant immune responses.
• To compare local flagellin-induced resistance with systemic acquired resistance.

Main Methods:

• Treatment of Arabidopsis plants with NHP and flg22.
• Analysis of metabolic and transcriptional changes.
• Biochemical and immune phenotyping of Arabidopsis mutants in NHP and SA biosynthesis pathways.
• Assessing plant immunity against Pseudomonas syringae and oomycete infections.

Main Results:

• NHP strongly primes flg22-induced accumulation of camalexin, SA biosynthesis, pipecolic acid (Pip) generation, and lipid accumulation.
• NHP more modestly primes flg22-triggered generation of amino acids and expression of FLG22-INDUCED RECEPTOR-KINASE1.
• NHP and SA mutually promote each other's biosynthesis and additively enhance camalexin formation during early infection stages.
• SA regulates NHP levels during later interaction periods.
• NHP and SA additively contribute to basal immunity and flagellin-induced acquired resistance.

Conclusions:

• NHP primes plants for robust metabolic and transcriptional defense responses to flagellin.
• NHP and SA have synergistic and regulatory interactions in plant immunity.
• NHP and SA contribute additively to basal and acquired resistance against various pathogens.
• NHP precursor Pip lacks independent immune activity.
• Mechanistic insights into flagellin-triggered resistance and SAR are revealed.