Metabolic interaction in algae with complex plastids

Our studies focus on organisms with complex plastids, such as Guillardia theta (Cryptophyta), Thalassiosira pseudonana (Heterocontophyta), Phaeodactylum tricornutum (Heterocontophyta) and Toxoplasma gondii (Apicomplexa). In contrast to the plastids of red and green algae, which are the result of cyanobacterial endosymbiosis, the complex plastids are formed by the uptake of a eukaryotic alga (green or red alga). Therefore, these organelles are not only separated from the cytosol by two, but mostly by four envelope membranes. This raises the question of how metabolic communication is organized within this consortium. In this context, it is worth mentioning that the number of potential plastid transporters is often higher in algae with complex plastids than in red or green algae. For example, the genome of the diatom Thalassiosira pseudonana contains eight sequences with similarities to plastid nucleotide transporters (NTTs). In contrast, only one NTT was identified in red algae, the precursors of complex plastids from diatoms. After biochemical characterization of selected plastidic transporters from red and green algae, diatoms, cryptomonads and Apicomplexa, their functional adaptation to the respective metabolic requirements in the different organisms can be documented.