Andrea Bräutigam - C4 photosynthesis – characterization, modeling, evolution

C4 photosynthesis enables plants to overcome the limitations of RubisCO because C4 photosynthesis concentrates CO2 at the site of Rubisco. C4 plants are thus highly productive and nitrogen- and water use efficient compared to C3 plants in the same environment. The C4 pathway is a cycle added to the standard C3 metabolism. Within the cycle the primary acceptor of CO2 is carboxylated to a C4 acid, hence the name, transferred, and decarboxylated to yield CO2 for the Calvin Benson Bassham cycle. The resulting C3 acid is transferred back and regenerated to the initial CO2 acceptor. While these general principles are conserved in all independently evolved origins of C4 photosynthesis, the types of decarboxylation enzymes and associated enzymes and transporters differ between species. Since the C4 cycle runs in multiple cell types in the leaf, mesophyll and bundle sheath cells which surround the veins, the C4 cycle requires changes to the biochemistry, to the cellular architecture, and to leaf architecture.

Comparative RNA-seq experiments in more than twelve C4 species revealed the molecular basis of the C4 cycle biochemistry and demonstrated idiosyncrasies of particular species (Kühlahoglu et al. 2014, summarized in Schlüter et al. 2016a). A combination of limited kinetic and stoichiometric modeling identified the mechanistic basis for a smooth fitness landscape during C4 evolution and confirmed photorespiration as the starting point for C4 evolution (Mallmann et al. 2014; Schlüter et al. 2016b). Anatomical adaptations such as chloroplast dimorphism were explained using kinetic models (unpublished) and the constraints for decarboxylation enzyme choice identified with stoichiometric models (unpublished). RandomForest based network construction has enabled first glimpses at possible regulatory circuits underlying regulation (unpublished).

In the presentation, I will summarize the published, descriptive RNA-seq approaches before I demonstrate how different types of models, be it kinetic, schematic, or stoichiometric, can be used to elucidate the principles and the evolutionary history which underlie the phenotypes we observe today.

http://www.plantcell.org/content/26/8/3243.short(link is external)

http://www.sciencedirect.com/science/article/pii/S1369526616300346(link is external)

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4103682/(link is external)

https://academic.oup.com/jxb/article/68/2/191/2339778/Photosynthesis-in-C3-C4-intermediate-Moricandia