Functional analysis of the starch related glucose 1-phosphate metabolism in higher plants

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Over the last years the biochemistry of starch metabolism is massively increased. The complexity is related to a concerted action of more than 30 evolutionary conserved enzymes and of various carbon fluxes related to starch syntheses as well as degradation. Recently, a direct transport of glucose 1-phosphate into Arabidopsis mesophyll cells and potato tuber cells and further into plastids (chloroplasts and amyloplast) was identified using in situ experiments. Moreover, a direct link of the up taken glucose 1-phosphate and starch turn-over was demonstrated. The molecular nature of the involved transporters as well as the detailed importance for starch metabolism is so far unclear. This proposal uses various experimental approaches and focuses on the following aspects:a) The identification of the involved glucose 1-phosphate transporters in Arabidopsis as well as in potato, including a detailed analysis of the specificity of the potentially transporters. Therefore, the transporters will be analysed expressed in yeast and/or Xenopus oocytes.b) The importance of the glucose 1-phosphate transport for starch metabolism will be analyzed by generating various Arabidopsis mutants lacking starch related enzymes in addition to the potentially glucose 1-phosphate transporters. The various mutants will be analyzed in respect to carbon fluxes and starch metabolism, including starch granule morphology, starch internal structure and starch related enzymes.c) In the various mutants the distribution of glucose 1-phosphate in different organs, tissues, and compartments will be analyzed using a highly sensitive assay for glucose 1-phosphate and non-aqueous fractionation.