Initiation of starch granules and regulation of the starch granule number per chloroplast in Arabidopsis thaliana

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Over the last years the knowledge about starch metabolism, especially about the transitory starch metabolism in Arabidopsis thaliana, is tremendously increased. However, some fundamental questions are still open. Thus, how starch granules are initiated and which regulatory processed exist do determine the number of starch granules per chloroplast. This is also important for starch industrial applications and biotechnology. Recently, two Arabidopsis lines were identified which show a strong reduction in the number of starch granules in the chloroplast, ss4 and dpe2/phs1. Using extensive analyses we showed that more than one pathway of starch initiation exists. Furthermore, we showed that the number of starch granules can be altered by changes in the light/dark regime and by modification of the starch degradation process. Thus, these mutants are an excellent tool to analyse the process of starch initiation in more detail.This proposal uses various experimental approaches and focuses on the following aspects:1. Detailed analyses of PHS1 and DPE2 influences on starch granule formation, by altering the light regime, by alteration of the expression, by expression of inactive versions of these enzymes to distinguish between metabolic or structural functions of the enzymes, and by identify interaction partners of the proteins. 2. Analysis of the specific starch granule parameters3. Modify the starch degradation to identify the link between starch degradation and starch granule initiation.