Rubisco proton production can improve CO2 acquisition
Rubisco is arguably the most abundant – and most important – protein on Earth. This enzyme stimulates photosynthesis, the process that plants use to convert sunlight into energy to fuel crop growth and yield. Rubisco’s role is to capture and fix carbon dioxide (CO2) sugar that feeds the operations of the plant. However, as much as Rubisco benefits plant growth, it can also operate at a notoriously slow pace which creates a barrier to photosynthetic efficiency.
About 20% of the time, Rubisco fixes oxygen (O2) molecules instead of CO2, costing the plant’s energy that could have been used to create yield. This time and energy consuming process is called photorespiration, where the plant sends its enzymes through three different compartments within the plant cell.
“However, many photosynthetic organisms have developed mechanisms to overcome some of Rubisco’s limitations,” said Ben Long who led this recent study published in PNAS for a research project called Achieve increased photosynthetic efficiency (WALL). RIPE, which is led by Illinois in partnership with the Australian National University (ANU), is the engineering of crops to be more productive by improving photosynthesis. RIPE is supported by the Bill and Melinda Gates Foundation, Food and Agriculture Research Foundationand United Kingdom Foreign, Commonwealth and Development Office.
“Among these organisms are microalgae and cyanobacteria from aquatic environments, which have Rubisco enzymes functioning efficiently in liquid protein droplets and protein compartments called pyrenoids and carboxysomes,” said lead researcher Long from the ANU Biology Research School.
It is not fully understood how these protein compartments contribute to Rubisco function. The ANU team sought to find the answer using a mathematical model focused on the chemical reaction conducted by Rubisco. As it collects the CO2 from the atmosphere, Rubisco also releases positively charged protons.
“Inside Rubisco compartments, these protons can accelerate Rubisco by increasing the amount of CO2 available. Protons do this by helping to convert bicarbonate to CO.2“Said Long.” Baking soda is the main source of CO2 in aquatic environments and photosynthetic organisms that use bicarbonate can tell us a lot about how to improve crop plants. ”
The mathematical model gives the ANU team a better idea of why these special compartments of Rubisco might improve the function of the enzyme and also gives them more information on how they may have evolved. One hypothesis from the study suggests that periods of low CO2 in Earth’s ancient atmosphere may have been the trigger for cyanobacteria and microalgae to evolve in these specialized compartments, when they could also be beneficial for organisms that grow in low-light environments.
The ANU members of the Realizing Increased Photosynthetic Efficiency (RIPE) project are trying to build these specialized Rubisco compartments in crop plants to help increase yield.
“The results of this study,” Long explained, “provide insight into the proper functioning of specialized Rubisco compartments and give us a better understanding of how we expect them to function in plants.
The RIPE project and its sponsors undertake to ensure Global Access and make project technologies available to farmers who need them most.
Article details: BM Long, B. Forster, SB Pulsford, GD Price, MR Badger, Proton production from Rubisco causes CO to rise2 in condensates and carboxisomes. PNAS in press doi: 10.1101 / 2020.07.08.125609 (2021).
Achieving Increased Photosynthetic Efficiency (RIPE) aims to improve photosynthesis and equip farmers around the world with higher yielding crops to ensure that everyone has enough food to lead healthy and productive lives. RIPE is sponsored by the Bill & Melinda Gates Foundation, the Food and Agriculture Research Foundation of America, and the UK Foreign, Commonwealth and Development Office.
RIPE is led by the University of Illinois in partnership with the Australian National University, Chinese Academy of Sciences, Commonwealth Scientific and Industrial Research Organization, Lancaster University, Louisiana State University, University of California, Berkeley, Cambridge University, University of Essex, and United States Department of Agriculture, Agricultural Research Service.
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