Metabolic engineering of plants for the synthesis of polyhydroxyalkanaotes

Synthesis of polyhydroxyalkanoates (PHAs) in crop plants is viewed as an attractive approach for the production of this family of biodegradable plastics in large quantities and at low costs. Synthesis of PHAs containing various monomers has so far been demonstrated in the cytosol, plastids, and peroxisomes of plants. Several biochemical pathways have been modified to achieve this, including the isoprenoid pathway, the fatty acid biosynthetic pathway, and the fatty acid β-oxidation pathway. PHA synthesis has been demonstrated in a number of plants, including monocots and dicots, and up to 40% PHA per gram dry weight has been demonstrated in Arabidopsis thaliana. Despite some successes, production of PHAs in crop plants remains a challenging project. PHA synthesis at a high level in vegetative tissues, such as leaves, is associated with chlorosis and reduced growth in some plants. The challenges for the future are to succeed in the synthesis of PHA copolymer with a narrow range of monomer composition, at levels that do not compromise plant productivity, and in creating methods for efficient and economical extraction of polymer from plants. These goals will undoubtedly require a deeper understanding of plant biochemical pathways as well as advances in biorefinery