Oxylipins, lipid derivatives generated by oxygenation of fatty acids, function in signaling pathways related to various environmental and pathological responses in both plants and animals. It is known that a variety of plant oxylipins have antimicrobial effects, stimulate plant defense gene expression, and regulate plant growth and development. The most well-characterized oxylipin in plants is the phytohormone jasmonic acid. This and other plant oxylipins are formed from the oxygenation of fatty acids, mainly linoleic acid and linolenic acid, by the action of lipoxygenases or α-dioxygenases, followed by various secondary transformations. The expression of genes encoding these enzyme activities is specifically induced upon inoculation with plant pathogens, and alterations in the synthesis of oxylipins in mutants and transgenic lines have been shown to modify the plant response to pathogen infection.
Vellosillo et al. (pages 831–846) used a collection of pure oxylipins and an in vitro seedling assay to study the functionality of oxylipins in physiological and pathological processes in Arabidopsis. Seedlings grown in the presence of oxylipins showed three distinct phenotypic alterations: root waving with lateral root arrest, growth arrest with loss of root apical dominance, and overall decrease of root elongation. Analysis of the results suggested a role for 9-hydroxyoctadecatrienoic acid, or a closely related 9-lipoxygenase product, in the formation of lateral roots and defense against pathogens via effects on gene expression, callose and pectin deposition, and the production of reactive oxygen species. The authors also analyzed several different oxylipin mutants, which revealed the presence of at least three distinct signaling pathways mediating oxylipin action.
Figure 1.
Phenotypes induced by oxylipins (normal phenotype in Murashige and Skoog medium on far left).