Expression of biodegradable plastics in plants

J.GODWIN

BTB-11-010

IntroductionPlants can be used as living factories to produce biodegradable plastics from renewable resources.

Poly(3-hydroxyalkanoates) are a group of biodegradable structurally simple macromolecules that are synthesized by several microorganisms.

The bacterium Ralstonia eutropha can synthesize PHB from glucose and store it as discrete granules to levels as high as 85% of the cell dry weight.

Biosynthesis of PHB

Generating transgenic plants for PHB synthesis

Transferring the complete phb operon, consisting of the phbC,phbA and phbB genes from Ralstonia eutropha.

The polyester PHB is derived from acetyl-CoA by a sequence of three enzymatic reactions

First condensation of two molecules of acetyl-CoA is catalyzed by β-ketothiolase to form acetoacetyl-CoA.

Acetyl-CoA reductase reduces acetoacetyl-CoA to β-hydroxybutyryl-CoA.

It is polymerized by PHB synthase to PHB.

Problems

There is an obvious need to improve transgenic PHB production by producing higher accumulation without side-effects such as

Chlorosis Male sterility Growth retardation

Inducible trans-activation in plastids

chloroplast transit peptide sequence + ethanol inducible promoter

Expression cassette for nuclear genome and plastid transformation

AchievementsTargeting of the polyhydroxybutyrate biosynthetic pathway to the plastids of Arabidopsis thaliana and Tobacco results in high levels of polymer accumulation.

Accumulation of PHB up to a concentration of 5% of dry weight has also been produced in the plastids of the hairy roots of sugar beet (Beta vulgaris L.) by nuclear transformation.

By targeting PHB synthesis to the plastids of maize and rape seed(Brassica napus).

Synthesis of polyhydroxybutyrate in fiber cells of Cotton with enhanced insulating properties.

APPLICATION AREAS

• Coated paper

• Agriculture mulch film

• Shopping bags

• Food waste films and bags

• Consumer packaging materials etc

Reference

Andreas Lössl, Karen Bohmert ,Hans Harloff , Christian Eibl , Stefan Mühlbauer and Hans-Ulrich Koop (2005).Inducible Trans-activation of Plastid Transgenes: Expression of the R.eutropha phb Operon in Transplastomic Tobacco. Plant Cell Physiology. 46(9): 1462–1471.

Christiane Nawrath, Yves Poirier, And Chris Somerville(1994).Targeting of the polyhydroxybutyrate biosynthetic pathway to the plastids of Arabidopsis thaliana results in high levels of polymer accumulation. Applied Biological Sciences Vol. 91, pp.12760-12764.

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