Exploring Algal Metabolic Fluxes for Greater Crop Yield

Haim Treves, Tel-Aviv University, Tel-Aviv, Israel (htreves@tauex.tau.ac.il)

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. Further perspectives may emerge from exploring algal diversity, especially under extreme environments. Specifically, a novel green alga, Chlorella ohadii, was recently isolated, exhibiting complete resistance to extreme illumination [Treves et al. 2017, Current Biology] and the fastest growth rate ever reported for a photosynthetic organism [Treves et al. 2020, Nature Plants].

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 Chlamydomonas reinhardtii, Chlorella sorokiniana and C. ohadii [Treves et al. 2022, Nature Plants]. This comprehensive metabolic study capitalized on recent progress made in analytical methods for phosphorylated intermediates separation and absolute quantification, and tools developed for measurement of carbon flux into end-products, including (ion-pair) reverse-phase LC-MS/MS and GC-MS. We estimated flux patterns in these algae 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. We will present our main findings and discuss their implications for future synthetic biology approaches aimed at improving photosynthesis, composition or growth of algae and plants. In an era where many are seeking ways to increase biomass production for alternative food and protein supply, the importance of metabolic engineering of targets arising from this study cannot be overestimated.