Research

There are presently three main axes of research within the LPB. These are:

1. metabolic engineering for the synthesis of polyhydroxyalkanoates

2. study of the peroxisomes and of fatty acid catabolism

3. phosphate transport and metabolism

These research projects are addressed using the tools of molecular and cellular biology, as well as genomics, with Arabidopsis thaliana being used as the main plant model, as well as Physcomitrella patens and the yeast Saccharomyces cerevisiae as a valuable complementary systems.

A full of publications can be found on the following link.

1. Metabolic engineering for the synthesis of polyhydroxyalkanoates

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 (fig1) 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. A variety of plant metabolic pathways located in various organelles are being studied and modified in order to supply substrates for PHA synthesis.Of particular interest is the metabolic engineering aimed at producing PHB and other PHAs in plant peroxisomes. In a collaborative research project initiated in 2006 with Dr. Steven Brumbley (University of Queensland), two ways of increasing the carbon flux to the peroxisomal PHA pathways are being explored, namely the down-regulation of the peroxisomal citrate synthase and the expression of a medium-chain acyl-ACP thioesterase (Fig.3).

2. Study of the peroxisomes and fatty acid catabolism

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).

3. Phosphate transport and metabolism

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.