Poly-(R)-3-hydroxybutyrate (PHB) is an aliphatic polyester with thermoplastic properties, which is naturally produced by certain bacteria as storage compound and is 100% biodegradable [1–5]. PHB is synthesized from acetyl-CoA by the action of three enzymes: a ketothiolase, an acetoacetyl-CoA reductase and a PHB synthase [6]. Under optimal conditions bacteria such as Ralstonia eutropha H16 can produce up to 80% PHB of cellular dry weight, and some companies have specialized on commercial PHB production (e.g. Metabolix Inc., Micromidas Inc.). Nevertheless, costs for PHB production by bacterial fermentation are still very high, which brought plants into focus as photosynthesis fueled low-cost production system [7–10]. The three bacterial enzymes were expressed in the cytosol or targeted to different compartments of the plant cell leading to high amounts of PHB accumulation in the plastids of Arabidopsis thaliana (up to 40% of dry weight) [11, 12]. However, due to stunted growth and infertility, these plants were not suitable for large-scale cultivation. Today, the highest levels of PHB synthesis in plants with fertile offspring are obtained in the plastid of Nicotiana tabacum resulting in up to 18% PHB of cellular dry weight [13].