Metabolic communication in secondary endosymbionts

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Guillardia theta belongs to a group of protists named cryptomonads that evolved by engulfment of an eukaryotic alga into a heterotrophic eukaryote. During the establishment of this consortium the symbiont has been reduced to a four-membrane exhibiting plastid still harbouring a vestigial nucleus in the periplastid space. We demonstrated that the former endosymbiont and the host perform a unique spatial separation of primary carbohydrate metabolism: Photosynthetically synthesized triose phosphates leave the chloroplast and cross the four envelope membranes into the cytosol, become converted to UDP-Glucose subsequently re-imported into the periplastid space for starch synthesis. For this complex metabolic route the cryptomonad use both, a novel type of plastidic triose-phosphate transporter and a so far unknown UDP-Glucose importer. Our aim is to characterize carriers and enzymes involved in this unique physiological communication in cryptomonads. This analysis will allow understanding a complex metabolic network as a consequence of secondary endosymbiosis. In addition, these studies will also promote the understanding of the metabolic interaction in human pathogenic apicomplexa in more detail. Latter contain an apicoplast also generated by a secondary endosymbiosis and also essential for primary metabolism.