The untapped potential of algal metabolic diversity
2Metabolic Networks, Max-Planck Institute of Molecular Plant Physiology, Germany
Photosynthesis-related pathways are regarded as a promising avenue for crop improvement. Whilst empirical studies have shown that photosynthetic efficiency is higher in microalgae than in C3 or C4 crops, the underlying reasons remain unclear. Using a tailor-made microfluidics labeling system to supply 13CO2 at steady state, we investigated in vivo labeling kinetics in intermediates of the Calvin Benson Cycle and sugar, starch, organic acid and amino acid synthesis pathways, and in protein and lipids in the algae Chlamydomonas reinhardtii, Chlorella sorokiniana and C. ohadii and compared them with published and new data from C3 and C4 plants. Our analyses identify distinct flux patterns supporting faster growth in photosynthetic cells, with some of the algae exhibiting faster RuBP regeneration, and increased fluxes through the lower glycolysis and anaplerotic pathways towards the tricarboxylic acid cycle, amino acid synthesis and lipid synthesis than in higher plants. In addition, algae exhibited distinct CBC metabolite profiles from plants, with low levels of pentose phosphates and, especially, high levels of ribulose 1,5-bisphosphate and 3-phosphoglycerate, which are required to generate concentration gradients that drive movement into and out of the algal CCM microcompartment (pyrenoid). These observations raise questions about how CBC regulation was modified during the evolution of algal CCMs and their subsequent loss in terrestrial plants, and highlight that operation of CCMs requires co-evolution of the CBC. We will present our main findings and discuss their implications for future synthetic biology approaches aimed at improving photosynthesis, composition or growth of higher plants.