Polyhydroxyalkanoate synthesis in transgenic plants as a new tool to study carbon flow through β‐oxidation

Abstract

SummaryTransgenic plants producing peroxisomal polyhydroxyalkanoate (PHA) from intermediates of fatty acid degradation were used to study carbon¯ow through the b-oxidation cycle. Growth of transgenic plants in media containing fatty acids conjugated to Tween detergents resulted in an increased accumulation of PHA and incorporation into the polyester of monomers derived from the b-oxidation of these fatty acids. Tween±laurate was a stronger inducer of b-oxidation, as measured by acyl-CoA oxidase activity, and a more potent modulator of PHA quantity and monomer composition than Tween±oleate. Plants co-expressing a peroxisomal PHA synthase with a capryl-acyl carrier protein thioesterase from Cuphea lanceolata produced eightfold more PHA compared to plants expressing only the PHA synthase. PHA produced in double transgenic plants contained mainly saturated monomers ranging from 6 to 10 carbons, indicating an enhanced¯ow of capric acid towards b-oxidation. Together, these results support the hypothesis that plant cells have mechanisms which sense levels of free or esteri®ed unusual fatty acids, resulting in changes in the activity of the b-oxidation cycle as well as removal and degradation of these unusual fatty acids through b-oxidation. Such enhanced ow of fatty acids through b-oxidation can be utilized to modulate the amount and composition of PHA produced in transgenic plants. Furthermore, synthesis of PHAs in plants can be used as a new tool to study the quality and relative quantity of the carbon¯ow through boxidation as well as to analyse the degradation pathway of unusual fatty acids.

Arabidopsis Lipins, PDAT1 Acyltransferase, and SDP1 Triacylglycerol Lipase Synergistically Direct Fatty Acids toward β-Oxidation, Thereby Maintaining Membrane Lipid Homeostasis

“…It thus appears that the endogenous b-oxidation capacity in leaves of Arabidopsis is sufficient to catabolize the additional FAs produced in tgd1-1 leaves. This lack of induction of b-oxidation is consistent with the finding that the activity of the b-oxidation cycle in vegetative tissues of Arabidopsis is inducible by unusual FAs but not by FAs normally associated with membrane lipids (Mittendorf et al, 1999).…”

Production of renewable polymers from crop plants

“…As a consequence, the polymer was soft and sticky. Arabidopsis mutants deficient in fatty acid desaturation reduced the number of double bonds in the mclPHA, while co-expression of a medium-chain acyl carrier protein (ACP) thioesterase from Cuphea lanceolata increased the C8-C12 monomer content in both leaves and seeds (Mittendorf et al, 1999;Poirier, 1999). In addition to the biotechnological aspects, synthesis of mclPHA in plants has been used as a valuable tool to study carbon flux through the b-oxidation cycle, as PHA accumulation reflects the carbon flux through the b-oxidation pathway, while monomer composition provides information on the type of fatty acids entering the cycle and how they are degraded (Poirier, 2002).…”

ACX3, a Novel Medium-Chain Acyl-Coenzyme A Oxidase from Arabidopsis

“…Several investigators (Eccleston and Ohlrogge, 1998;Mittendorf et al, 1999) have shown that accumulation of unusual fatty acids such as MCFA leads to increased expression of ␤-oxidation enzymes. As the first step toward metabolic regulation of ␤-oxidation, we have employed northern-blot analysis to examine the presence of an AtACX3 homolog in developing and germinating B. napus seeds (Fig.…”