Characterization of growth, bacterial population and cadmiumresponsen of ccr mutant Arabidopsis thaliana and the potential of endophytes to increase the biomass and phytoremediation-efficiency (R-3579)

The competition for cultivating food and biomass crops is a raising problem. This problem can be limited by growing lignocellulosic biomass (eg willow or poplar) on less fertile soils. In an ideal case, the woody plants can be grown on marginal soils (including cadmium (Cd) contaminated soils). An additional advantage is the decontamination of these polluted soils by making use of plants (phytoremediation). During processing the lignocellulose biomass to pure cellulose fibers, the recalcitrance of lignin polymers is a major limiting factor. Genetically modified crops with lower lignin contents (including down regulation of cinnamoyl-CoA-reductase (CCR)) can increase the efficiency of this process. However, the modification will have a negative influence on the growth and development of the plant and may affect the soluble phenolics inside the xylem. In this project Arabidopsis thaliana is used as model organism and Cd as model contaminant. The obtained knowledge can afterwards be extrapolated to economically valuable field applications where woody, fast-growing plants are used. The following 2 objectives are envisaged in my PhD: (1) the characterization of the differences between A. thaliana WT and a ccr-mutant at the level of the plant and its associated bacterial population, and (2) to improve the production of biomass and Cd-uptake by making use of growth-promoting bacteria. These objectives will be tested on four conditions: wild-type and ccr-mutated A. Thaliana, with and without exposure to Cd. During objective 1 the growth phases will be investigated for the shoots (method of Boyes) and the roots (vertical agar plate). Furthermore, parameters such as biomass, activity of stress-related enzymes (spectrophotometry), the expression of genes responsible for stress-related enzymes (rt-PCR), the chlorophyll content (spectrophotometry) and Cd uptake (acid and heat degradation, flame atomic absorption spectrophotometry)are examined in plants grown in hydroponics. Also, the phenolic compounds inside the xylem (HPLC, LC-MS-MS) and lignin (Klason, thioacidolysis) are analyzed. At the level of the bacterial population, both cultivable and non-cultivable bacteria genotypically (ARDRA, DGGE) and phenotypic (colorimetric tests, Biolog plates) are tested. In objective 2 the inoculation process in a hydroponic system is optimized followed by a screening of the most promising (in vitro) growth-promoting bacteria. Afterwards, the best endophyte is selected for extensive testing at the level of the plant as described in objective 1. The project is implemented in the Centre for Environmental sciences that possesses expertise in the use of plant-associated bacteria to increase the phytoremediation efficiency and A. thaliana. In addition, this project is a collaboration with Prof. Dr. Wout Boerjan of the Bioenergy Group (Department of Plant Systems Biology, UGent) for the lignin-related part. Furthermore, a internship is planned at the Institute for Agrobiological Research in Galicia (Santiago de Compostela) (IIAG) that is part of the Spanish National Research Council (CSIC). The study of the genetic composition of the total bacterial population occurs in Spain under the leadership of Prof. Dr. Petra Kidd.

Keywords:Arabidopsis thaliana, Cadmium, Endofytes, PHYTOREMEDIATION

Disciplines:Plant biology