Role of Peroxisomal beta-Oxidation in the Production of Plant Signaling Compounds.

The lipid-derived signaling compound jasmonic acid (JA) regulates a wide variety of developmental and defense-related processes in higher plants. JA synthesis is initiated in the plastid and completed in peroxisomes. The peroxisomal reactions involve reduction of 12-oxo-phytodienoic acid (OPDA) to 3-oxo-2-(2'-pentenyl)-cyclopentane-1-octanoic acid (OPC-8:0), which is subsequently converted to JA by three rounds of beta-oxidation. It is widely assumed that JA precursors are activated to their CoA derivatives prior to entering the beta-oxidation cycle. However, acyl-activating enzymes (AAEs) that catalyze this reaction in vivo have remained elusive, owing in part to the large size and functional redundancy of the AAE gene family. In a recent issue of The Journal of Biological Chemistry, we reported the use of coexpression analysis to identify an AAE gene that is coordinately regulated with known JA biosynthetic components in Arabidopsis. A combination of genetic, biochemical, and cellular approaches was used to demonstrate that this gene, called OPC-8:0 CoA Ligase1 (OPCL1), has a physiological role in activating JA precursors in the peroxisome. Similar approaches may be useful for identifying additional components of the jasmonate pathway, as well as AAEs that participate in the synthesis of other plant signaling compounds.