Metabolic communication in secondary endosymbionts

Guillardia theta属于一组原生生物，名为隐单胞藻，通过吞噬真核藻类进化成异养真核生物。在这个联合体的建立过程中，共生体被减少到一个四层膜，显示出质体，但在周质体腔中仍有一个残留的核。我们证明了以前的内生菌和寄主在初级碳水化合物代谢中执行了独特的空间分离：光合作用合成的磷酸三糖离开叶绿体，穿过四个被膜进入细胞质，转化为UDP-葡萄糖，然后重新输入到周质体内合成淀粉。对于这一复杂的代谢途径，隐形单胞菌同时使用一种新型的可塑性磷酸三糖转运体和一种迄今未知的UDP-葡萄糖转运体。我们的目标是确定隐形单胞菌中参与这种独特生理通讯的载体和酶的特征。这一分析将使我们能够理解次级内共生的复杂代谢网络。此外，这些研究还将促进对人类致病性尖端复合体代谢相互作用的更详细的了解。后者含有顶体，也是由次级内共生产生的，也是初级新陈代谢所必需的。

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.