Polyhydroxyalkanoates (PHAs) are bacterial polyesters which can be used as bio-based and biodegradable plastic materials. The development of bioplastics which are produced from renewable carbon sources is a very important step for reducing the emission of carbon dioxide. Since the thermal and physical properties of PHAs are variable depending on their monomer composition, PHAs can be processed to various materials, such as fibers, films and elastomer. Although PHAs are useful and environmentally friendly material, high cost of production has limited widespread use of PHAs. The most proteins involved in PHA biosynthesis, such as PHA synthases, monomer supplying enzymes, coat proteins of PHA inclusion, and their regulators, have been cloned and characterized. PhaR is the regulator of PHA biosynthesis, and has a unique ability to bind to DNA and PHA. Recently, artificially modified PHA biosynthetic enzymes were generated by the in vitro evolutionary approach. The modified enzymes enabled us to increase the PHA content and regulate the monomer composition. The photosynthetic PHA production by the transgenic plants harboring PHA biosynthetic genes has been investigated to reduce the cost of PHA production. The targeting of enzyme into plastid and the application of highly active mutated PHA synthases enhanced PHA accumulation in plants.

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