Samenvatting

Nitrogen is essential for most plant growth which they take up from the soil. Some plants can form a symbiotic relationship with certain Rhizobia soil bacterium, which will reduce nitrogen molecules into ammonia, by a process called nitrogen fixation. Medicago truncatula is a plant model system used to study nitrogen fixation. The process starts when M. truncatula sends out flavonoids to attract Rhizobia bacterium. Rhizobia invades the root hairs, where they elongate and form an infection thread till they reach the primordium cells. This is where the bacteroids start to divide and form a nodule, which in a later stadium can convert nitrogen. In our study we investigate the function and localization of certain proline-rich proteins (PRP’s) involved in the nodule forming. PRP’s are all structural proteins in the plant cell wall and some of them are already known as early nodulin genes. Early nodulin genes are only expressed after infection with Rhizobium bacteria. To maintain our goal we produced 6 different knockdown lines, using Agrobacterium rhizogenes to insert our hairpin construct into the M. truncatula root system. So far our results show that the knockdown of the PRP1 protein results in a big change in their cell arrangement. The roots itself seem to be swollen and they do not grow as fast as wilt type hairy roots. The cells in the cortex are disorganized and empty gabs fall in between. Immunoblotting indicated that the RNAi knockdown of the PRP2 gene did not reduce the expression. For the Forever Young genewe can say tahat our results indicate that a reduction of this gene is lethal. Most roots died in an early stage of growth. Experiments with the inducible pOp6 promoter will hopefully confirm this in the future.