Role of chloroplast trienoic fatty acids in plant disease defense responses

Abstract

<jats:title>Summary</jats:title><jats:p>Trienoic fatty acids (TAs) are the major polyunsaturated fatty acid species in the membrane lipids in plant cells. TAs are crucial for the adaptation to abiotic stresses, especially low‐ or high‐temperature stress. We show that TAs in chloroplast membrane lipids are involved in defense responses against avirulent bacterial pathogens. Avirulent pathogen invasion of plants induces a transient production of reactive oxygen intermediates (ROI), programmed cell death and subsequent disease resistance. The Arabidopsis <jats:italic>fad7fad8</jats:italic> mutation, which prevents the synthesis of TAs in chloroplast lipids, caused the reduction in ROI accumulation in leaves inoculated with <jats:italic>Pseudomonas syringae</jats:italic> pv. <jats:italic>tomato</jats:italic> DC3000 (<jats:italic>avrRpm1</jats:italic>). Linolenic acid, the most abundant TA, activated the NADPH oxidase that is responsible for ROI generation. TAs were transferred from chloroplast lipids to extrachloroplast lipids coincident with ROI accumulation after inoculation with <jats:italic>Pst</jats:italic> DC3000 (<jats:italic>avrRpm1</jats:italic>). Furthermore, the <jats:italic>fad7fad8</jats:italic> mutant exhibited reduced cell death and was compromised in its resistance to several avirulent <jats:italic>P. syringae</jats:italic> strains. These results suggest that TAs derived from chloroplast lipids play an important role in the regulation of plant defense responses.</jats:p>

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