Production of novel biopolymers in plants: recent technological advances and future prospects

•Plant production of novel polymers increases materials available from agriculture.•Synthesis of PHB illustrates challenges of plant-based production of novel materials.•PHB can be produced at high levels in biomass and oil seed crops.•Competition for substrate from endogenous pathways limits PHB and/or plant yield.•Future efforts should focus on increasing substrate for PHB synthesis and plant growth. The production of novel biopolymers in plants has the potential to provide renewable sources of industrial materials through agriculture. In this review we will highlight recent progress with plant-based production of polyhydroxyalkanoates (PHAs), silk, elastin, collagen, and cyanophycin with an emphasis on the synthesis of poly[(R)-3-hydroxybutyrate] (PHB), a renewable biodegradable PHA polymer with potential commercial applications in plastics, chemicals, and feed markets. Improved production of PHB has required manipulation of promoters driving expression of transgenes, reduction in activity of endogenous enzymes in competing metabolic pathways, insertion of genes to increase carbon flow to polymer, and basic plant biochemistry to understand metabolic limitations. These experiments have increased our understanding of carbon availability and partitioning in different plant organelles, cell types, and organs, information that is useful for the production of other novel molecules in plants.