Exploring the intricacies of Rubisco expression and evolution across marine ecosystems and its ability to enhance photosynthesis in key agricultural crops

Abstract

Marine environments are responsible for 50% of the net primary fixation of carbon globally. Predominantly, the Calvin Benson Basham cycle fixes carbon with the initial enzyme being Rubisco. Rubisco has been shown to be a significant bottleneck in photosynthesis, due to a slow catalytic rate and promiscuity of the enzyme. Previous Rubisco studies have largely focused on land plants, and little is known about the diversity and abundance of Rubisco within marine environments. Through analysing publicly available metagenomes and metatranscriptomes from the Earth’s seas and oceans; we have begun to paint a picture of the global abundance and variation of Rubisco alongside adjoining photosynthetic apparatus. Additionally phylogenetic and sequence analysis alongside machine learning models was used to highlight regions of the Rubisco gene under selective pressure, linking selection to metagenome environment. Finally, the big leaf photosynthesis model was applied to simulate heterogenous expression of aquatic Rubisco in wheat over an entire growing season. Transcriptomic analysis showed a significant correlation with temperature across the earth’s oceans. On top of this, sequence analysis of Rubisco structures provides evidence for adaption of the large and small subunit to differing environmental temperatures, additionally demonstrating residues that diverge in warm(>20oC) and cold (<10OC) ecological systems. In particular the ßE-ßF loop of the form ID Rubisco small subunit was highlighted as a region under widespread positive selection across phylogenetic lineages in marine environments. Finally, photosynthesis modelling efforts showed that Rubisco from form ID Rubisco, particularly G. monillis could simultaneously improve carbon fixation and improve water usage in wheat. Overall, this study provides an invaluable insight into the regulation and evolution of Rubisco in the Earth’s ocean, generating an impetus for further investigation. Additionally modelling efforts demonstrate the potential benefits of expressing aquatic Rubisco in economically important crop species to improve future food security.