Poster: Hormone synthesis & metabolism
Abs #
478: Characterization of an acyl-CoA oxidase involved in jasmonic acid biosynthesis
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Presenter: |
Schilmiller, Anthony L, schilmil@msu.edu |
Authors | Schilmiller, Anthony L (A) Li, Chuanyou (B) Howe, Gregg (A) | | Affiliations: |
(A): Dept. of Energy Plant Research Laboratory and Dept. of Biochemistry and Molecular Biology, Michigan State University
(B): Dept. of Energy Plant Research Laboratory, Michigan State University
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Jasmonic acid (JA) is synthesized from linolenic acid by the octadecanoid pathway, and acts as a potent regulator of stress-induced gene expression in plants. Biochemical and genetic approaches have been used to identify nearly all of the enzymes involved in JA biosynthesis. The first three steps in the pathway occur in the chloroplast where lipoxygenase, allene oxide synthase, and allene oxide cyclase sequentially convert linolenic acid to the first cyclic intermediate, 12-oxo-phytodienoic acid (OPDA). The cyclopentenone ring of OPDA is then reduced by OPDA reductase (OPR3) in the peroxisome to yield 3-oxo-2(2’[Z]-pentenyl)-cyclopentane-1-octanoic acid (OPC-8). The final steps of JA synthesis presumably require three cycles of peroxisomal β-oxidation to remove six carbons from the octanoate side-chain of OPC-8, but direct evidence for this has so far been lacking. We are using tomato as a model system to investigate the role of β-oxidation in JA biosynthesis and wound-induced signaling. Current efforts are focused on the characterization of acyl-CoA oxidase (ACX), which catalyzes the first and rate-limiting step of fatty acid β-oxidation in peroxisomes. Genetic studies indicated that loss of function of one member (called ACX1) of the ACX family of proteins in tomato results in a severe deficiency in wound-induced JA biosynthesis. The LeAXC1 gene is expressed in tissues that are active in JA biosynthesis. Biochemical analysis of recombinant LeACX1 indicated that it is an FAD-containing enzyme that has broad specificity for fatty acyl-CoAs, including OPDA-CoA. These findings provide the first example of a specific β-oxidation pathway enzyme involved in JA biosynthesis.
