Analysis of the alternative pathways for the beta-oxidation of unsaturatedfatty acids using transgenic plants synthesizing polyhydroxyalkanoates in peroxisomes

Degradation of fatty acids having cis-double bonds on even-numbered carbons requires the presence of auxiliary enzymes in addition to the enzymes of t he core beta -oxidation cycle. Two alternative pathways have been described to degrade these fatty acids. One pathway involves the participation of th e enzymes 2,4-dienoyl-coenzyme A (CoA) reductase and Delta (3)-Delta (2)-en oyl-CoA isomerase, whereas the second involves the epimerization of R-8-hyd roxyacyl-CoA via a 3-hydroxyacyl-CoA epimerase or the action of two stereo- specific enoyl-CoA hydratases. Although degradation of these fatty acids in bacteria and mammalian peroxisomes was shown to involve mainly the reducta se-isomerase pathway, previous analysis of the relative activity of the eno yl-CoA hydratase II (also called R-3-hpdroxpacyl-CoA hydro-lyase) and 2,4-d ienoyl-CoA reductase in plants indicated that degradation occurred mainly t hrough the epimerase pathway. We have examined the implication of both path ways in transgenic Arabidopsis expressing the polyhydroxyalkanoate synthase from Pseudomonas aeruginosa in peroxisomes and producing polyhydroxyalkano ate from the 3-hydroxyacyl-CoA intermediates of the beta -oxidation cycle. Analysis of the polyhydroxpalkanoate synthesized in plants grown in media c ontaining cis-10-heptadecenoic or cis-10-pentadecenoic acids revealed a sig nificant contribution of both the reductase-isomerase and epimerase pathway s to the degradation of these fatty acids.