Increased flow of fatty acids toward beta-oxidation in developing seeds ofArabidopsis deficient in diacylglycerol acyltransferase activity or synthesizing medium-chain-length fatty acids

Synthesis of polyhydroxyalkanoates (PHAs) from intermediates of fatty acid beta-oxidation was used as a tool to study fatty acid degradation in develo ping seeds of Arabidopsis. Transgenic plants expressing a peroxisomal PHA s ynthase under the control of a napin promoter accumulated PHA in developing seeds to a final level of 0.06 mg g(-1) dry weight. In plants co-expressin g a plastidial acyl-acyl carrier protein thioesterase from Cuphea lanceolat a and a peroxisomal PHA synthase, approximately 18-fold more PHA accumulate d in developing seeds. The proportion of 3-hydroxydecanoic acid monomer in the PHA was strongly increased, indicating a large flow of capric acid towa rd beta-oxidation. Furthermore, expression of the peroxisomal PHA synthase in an Arabidopsis mutant deficient in the enzyme diacylglycerol acyltransfe rase resulted in a 10-fold increase in PHA accumulation in developing seeds . These data indicate that plants can respond to the inadequate incorporati on of fatty acids into triacylglycerides by recycling the fatty acids via b eta-oxidation and that a considerable flow toward beta-oxidation can occur even in a plant tissue primarily devoted to the accumulation of storage lip ids.