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Poly(beta-hydroxybutyrate) production in oilseed leukoplasts of Brassica napus. Planta (Berlin) 209, 547-550.
| Houmiel K.L., Slater, Steven, Broyles, Debra, Casagrande, Laura, Colburn, Susan, Gonzalez, Kathleen, Mitsky, Timothy A., Reiser, Steven E., Shah, Devang, Taylor, Nancy B., Tran, Mintien, Valentin, Henry E., Gruys, Kenneth J. (1999).
| 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 aceto-acetyl-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.
Polyhydroxyalkanoates (PHAs), a class of biodegradable polymers, offer an environmentally sustainable alternative to petroleum-based plastics. A beta-ketothiolase, an aceto-acetyl-CoA reductase and a poly(beta-hydroxy butyrate) synthase (PHB synthase) from the bacterium Ralstonia eutropha were independently engineered behind the seed specific Lesquerella fendleri oleate 12-hydrocylase promoter in a modular fashion and transformed into Brassica napususing Agrobacterium. Leukoplasts of transformed plants accumulated between 0.02-7.7% PHB of fresh seed weight of mature seeds, with most (91%) of the plants producing polymer within the 0-3.0% range and preliminary studies indicate that oil production was not impacted by polymer production. Commercial production will require approximately twice the amount of PHA accumulation achieved here.
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