Schematic illustration of important metabolic and genetic information pathways in NoAz.

The left cell represents a vegetative cell while the right a nitrogen-fixing heterocyst. Red color indicates pseudogenes lacking a functional counterpart in the NoAz genome. Orange indicates pseudogenes where a functional counterpart is present elsewhere in the genome. Fully functional gene(s) are illustrated (blue) only if their function is linked to other processes in the figure. The localization of pathways in vegetative cells or heterocysts is representative only for nitrogen fixation (heterocysts) and PSII activity (vegetative cells). Note that only a minor part of the nitrogen fixed in heterocysts is incorporated using the GS-GOGAT pathway and used for synthesis of amino acids, while most is exported to the plant as NH3. Sugar is provided by the plant in an as yet unknown form; putatively imported via the sugar phosphotransferase system (PTS). Function has been lost in the glycolytic pathway as the pfkA gene, encoding 6-phosphofructokinase, is a pseudogene and sugar metabolism in the Azolla cyanobiont probably proceeds via the Oxidative Pentose Phosphate Pathway (OPPP). Extensive loss of function is evident among genes involved in uptake and transport of nutrients and NoAz has lost the capacity to both import and metabolise alternative nitrogen sources. Table S3 shows detailed information on genes indicated in the figure and their closest homologs in other filamentous heterocystous cyanobacteria.