There are presently three main axes of research within the LPB. These are:
Polyhydroxyalkanoates (PHA) form a family of polyesters of 3-hydroxyacids
naturally synthesised by a wide variety of bacteria as a carbon storage and
energy reserve (Fig.1) PHAs
have attracted interest because of their properties as natural and biodegradable
thermoplastics and elastomeric materials. PHAs could be used as attractive
alternatives to the petroleum-derived plastics that pollute our environment
(Fig.2). Synthesis of PHA in
plants is likely to be the only way of producing PHA at a low cost and in
sufficiently large quantities for their use as a plastic substitute in every-day
consumer products.
Synthesis of PHA in the plant Arabidopsis thaliana has first been demonstrated
in 1992 by Yves Poirier and Chris Somerville. Since then, the LPB has worked
at both increasing the quantity of PHA produced in plants as well as on extending
the range of PHA polymers that could be produced in plants to include a range
of polymers having properties of flexible plastics, elastomers and glues (Fig.3).
A variety of plant metabolic pathways located in various organelles are being
studied and modified in order to supply substrates for PHA synthesis. Such
pathways include fatty acid biosynthesis in the plastid and fatty acid degradation
in the peroxisome.
Synthesis of polyhydroxyalkanotes in plants provides not only the mean to produce valuable biopolymers, but also provides a novel and unique tool to study plant metabolic pathways. The LPB has recently developed PHA synthesis in the peroxisome, using the intermediates of fatty acid degradation via the beta-oxidation pathway, as a tool to study carbon flux through the degradative pathway (Fig.4). Using this system, fundamental aspect of fatty acid and lipid biosynthesis and degradation are being studied, including the biochemical pathway involved in the turnover of unsaturated and unusual fatty acids, factors influencing the maintenance of membrane lipid composition, the presence of metabolic channelling, etc. These studies are pursued using both Arabidopsis thaliana and yeast (Fig.5). The use of PHA as a metabolic marker of fatty acid degradation is being used in the CONFAB EU project aimed at controlling the breakdown of fatty acids for improving the production of novel oils in plants.
Inorganic phosphate (Pi) is one of the main nutrients limiting the growth of plants and a major ingredient of fertilisers used in agriculture. Unfortunately, a substantial proportion of Pi supplied in agriculture eventually reaches the ground water, as well as rivers and lakes, favouring the growth of algae and leading to water eutrophication. In order to reduce the use of Pi in agriculture, plants capable of growing optimally in soil with a reduced Pi content must be developed. The work of the LPB on Pi transport and metabolism is presently focussed on the characterisation of a novel family of protein recently isolated in Arabidopsis. The PHO1 gene of Arabidopsis is involved in the loading of Pi from the root into the xylem vessels. The gene was isolated by positional cloning using the Arabidopsis pho1 mutant (Fig.6). The PHO1 gene is expressed predominantly in the root vascular system, in good agreement with the role of PHO1 in Pi efflux out of the stelar cells for loading Pi to the xylem (Fig.7). A family of 10 genes related to PHO1 have recently been identified from the Arabidopsis genome project. Our main goal is to gain a comprehensive view of the role of these genes in phosphate acquisition and distribution throughout the plant.