title: Poly(beta-hydroxybutyrate) production in oilseed leukoplasts of brassica napus
abstract: Polyhydroxyalkanoates (PHAs) comprise a class of biodegradable polymers which offer an environmentally sustainable alternative to petroleum-based plastics. Production of PHAs in plants is attractive since current fermentation technology is prohibitively expensive. The PHA homopolymer poly(beta-hydroxybutyrate) (PHB) has previously been produced in leaves of Arabidopsis thaliana (Nawrath et al., 1994, Proc Natl Acad Sci USA 91: 12760-12764). However, Brassica napus oilseed may provide a better system for PHB production because acetyl-CoA, the substrate required in the first step of PHB biosynthesis, is prevalent during fatty acid biosynthesis. Three enzymatic activities are needed to synthesize PHB: a beta-ketothiolase, an acetoacetyl-CoA reductase and a PHB synthase. Genes from the bacterium Ralstonia eutropha encoding these enzymes were independently engineered behind the seed-specific Lesquerella fendleri oleate 12-hydroxylase promoter in a modular fashion. The gene cassettes were sequentially transferred into a single, multi-gene vector which was used to transform B. napus. Poly(beta-hydroxybutyrate) accumulated in leukoplasts to levels as high as 7.7% fresh seed weight of mature seeds. Electron-microscopy analyses indicated that leukoplasts from these plants were distorted, yet intact, and appeared to expand in response to polymer accumulation.
authors.affiliation: Monsanto Company, Agricultural Sector, 700 Chesterfield Parkway North, St. Louis, MO 63198, USA.
authors.initials: KL
authors.lastname: Houmiel
authors.initials: S
authors.lastname: Slater
authors.initials: D
authors.lastname: Broyles
authors.initials: L
authors.lastname: Casagrande
authors.initials: S
authors.lastname: Colburn
authors.initials: K
authors.lastname: Gonzalez
authors.initials: TA
authors.lastname: Mitsky
authors.initials: SE
authors.lastname: Reiser
authors.initials: D
authors.lastname: Shah
authors.initials: NB
authors.lastname: Taylor
authors.initials: M
authors.lastname: Tran
authors.initials: HE
authors.lastname: Valentin
authors.initials: KJ
authors.lastname: Gruys