2. Introduction
Plants 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.
4. 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.
5. 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
9. Achievements
Targeting 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.
10. APPLICATION AREAS
• Coated paper
• Agriculture mulch film
• Shopping bags
• Food waste films and bags
• Consumer packaging materials etc
11. 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.
Editor's Notes
Polyhydroxyalkanoates (PHAs) like the poly-3-hydroxybutyrate (PHB), polyhydroxyvalerate (PHV) and polyhydroxyhexanoate (PHH);Poly(3-hydroxybutyrate) (PHB) has been studied most extensively and has triggered commercial interest in this class of polymers.
InRalstoniaeutropha, the genes for these enzymes are organized in a single operon.
TPSS, DNA sequence for the transit peptide of the small subunitof RuBisCoThe aadA cassette used for spectinomycin selection wasexpressed constitutively by the 16S rRNA promoter with the terminationregion from a ChlamydomonasrbcL gene (TrbcLC)
Although most work on PHB biosynthesis has been done in the model plant A. thaliana. high accumulation of PHB in commercial crop plants.
