SYNTHESIS OF MEDIUM-CHAIN-LENGTH POLYHYDROXYALKANOATES IN ARABIDOPSIS-THALIANA USING INTERMEDIATES OF PEROXISOMAL FATTY-ACID BETA-OXIDATION

Polyhydroxyalkanoate (PHA) is a family of polymers composed primarily of R-3-hydroxyalkanoic acids, These polymers have properties of biodeg radable thermoplastics and elastomers. Medium chain-length PHAs (MCL-P HAs) are synthesized in bacteria by using intermediates of the beta-ox idation of alkanoic acids, To assess the feasibility of producing MCL- PHAs in plants, Arabidopsis thaliana mas transformed with the PhaC1 sy nthase from Pseudomonas aeruginosa modified for peroxisome targeting b y addition of the carboxyl 34 amino acids from the Brassica napus isoc itrate lyase, Immunocytochemistry demonstrated that the modified PHA s ynthase was appropriately targeted to leaf-type peroxisomes in light-g rown plants and glyoxysomes in dark-grown plants. Plants expressing th e PHA synthase accumulated electron-lucent inclusions in the glyoxysom es and leaf-type peroxisomes, as well as in the vacuole, These inclusi ons were similar to bacterial PHA inclusions. Analysis of plant extrac ts by GC and mass spectrometry demonstrated the presence of MCL-PHA in transgenic plants to approximately 1 mg per g of dry weight. The plan t PHA contained saturated and unsaturated 3-hydroxyalkanoic acids rang ing from six to 16 carbons with 41% of the monomers being 3-hydroxyoct anoic acid and 3-hydroxyoctenoic acid, These results indicate that the beta-oxidation of plant fatty acids can generate a broad range of R-3 -hydroxyacyl-CoA intermediates that can be used to synthesize MCL-PHAs .