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A team of scientists from the University of Essex has increased the productivity of crops by 27 percent by dissolving two bottlenecks in photosynthesis – the process by which plants fix carbon dioxide in the sugars that feed crop growth. Chidi Afamefule (left) maintains an unmodified control plant, while Kenny Brown (center) maintains a plant modified to solve one bottleneck, and Patricia Lopez-Calcagno (right) maintains a plant adapted to solve two bottlenecks loose. Credit: RIPE Project / Claire Benjamin
Plants are factories that produce light and carbon dioxide yields – but parts of this complex process, called photosynthesis, are hampered by a shortage of raw materials and machinery. To optimize production, scientists from the University of Essex have solved two major photosynthetic bottlenecks to increase plant productivity by 27 percent in real field conditions, according to a new study published in Nature Plants. This is the third breakthrough for the research project Realizing Increased Photosynthetic Efficiency (RIPE); however, this photosynthetic hack has also been shown to conserve water.
“Like a factory line, plants are only as fast as their slowest machines,” said Patricia Lopez-Calcagno, a postdoctoral researcher at Essex, who led this work for the RIPE project. “We have identified some slower steps, and what we are doing is allowing these plants to build more machines to accelerate these slower steps in photosynthesis.”
The RIPE project is an international effort led by the University of Illinois to develop more productive crops by enhancing photosynthesis – the natural, sunlight-driven process that all plants use to fix carbon dioxide in sugars that grow, develop and finally throw up. RIPE is supported by the Bill & Melinda Gates Foundation, the US Foundation for Food and Agriculture Research (FFAR), and the UK Government Department of International Development (DFID).
The productivity of a factory decreases as supplies, transport channels, and reliable machines are limited. To find out what limits photosynthesis, researchers have modeled each of the 170 steps of this process to identify how plants can produce sugar more efficiently.
In this study, the team increased crop growth by 27 percent by solving two constraints: one in the first part of photosynthesis where plants convert light energy into chemical energy and one in the second part where carbon dioxide is fixed in sugars.
Within two photosystems, sunlight is captured and converted into chemical energy that can be used for other processes in photosynthesis. A transport protein called plastocyanin moves electrons into the photosystem to fuel this process. But plastocyanin has a high affinity for its acceptor protein in the photosystem, so it hangs around it, and it fails to move electrons back and forth efficiently.
The team addressed this initial bottleneck by helping plastocyanin share the charge with the addition of cytochrome c6 – a more efficient transport protein that has a similar function in algae. Plastocyanin requires copper and cytochrome requires iron to function. Depending on the availability of these nutrients, algae can choose between these two transport proteins.
At the same time, the team improved a photosynthetic bottleneck in the Calvin-Benson cycle – in which carbon dioxide is bound in sugars – by bulging up the amount of a key enzyme called SBPase, borrowing the extra cellular machine from another plant species. and cyanobacteria.
By adding “cellular forklifts” to electron transport in the photo systems and “cellular machine” for the Calvin Cycle, the team also improved the efficiency of the use of the crop, as the ratio of biomass produced to water lost by the plant.
“In our field tests, we discovered that these plants use less water to produce more biomass,” said lead researcher Christine Raines, a professor at the School of Life Sciences at Essex, where she also serves as the vice chancellor for research. . “The mechanism responsible for this additional improvement is not yet clear, but we are continuing to investigate this to help us understand why and how it works.”
Field trials of 2016 conducted on the Energy Farm of the University of Illinois. Credit: Brian Stauffer / University of Illinois
These two improvements, when combined, have been shown to increase crop productivity by 52 percent in glasshouse cultivation. More importantly, this study showed up to a 27 percent increase in crop growth in field trials, which is the real test of any crop improvement – showing that these photosynthetic hacks can stimulate crop production in real growth conditions.
“This study offers the exciting opportunity to potentially combine three proven and independent methods to achieve 20 percent increases in crop productivity,” said RIPE Director Stephen Long, Ikenberry Endowed University Chair of Plant Sciences and Plant Biology at the Carl R. Woese Institute for Genomic Biology in Illinois. “Our modeling suggests that stacking this breakthrough with two previous discoveries from the RIPE project could result in additive yield gains totaling 50 to 60 percent in food crops.”
RIPE’s first discovery, published in Science, helped plants adapt to changing light conditions to increase yields by as much as 20 percent. The second breakthrough of the project, also published in Science, made a shortcut to how plants deal with a glitch in photosynthesis to increase productivity by 20 to 40 percent.
Next, the team plans to translate these discoveries from tobacco – a model crop used in this study as a test bed for genetic improvements, because it is easy to manipulate, grow and test – to food crops like cassava, cowpea , staple corn, soy and rice needed this century to feed our growing population. The RIPE project and its sponsors are committed to guaranteeing Global Access and making the project’s technologies available to the farmers who need it most.
Reference: “Stimulating Photosynthetic Processes Increases Productivity and Efficiency for Field Use” by Patricia E. López-Calcagno, Kenny L. Brown, Andrew J. Simkin, Stuart J. Fisk, Silver Vialet-Chabrand, Tracy Lawson, and Christine A Raines, 10 August 2020, Natural plants.
DOI: 10.1038 / s41477-020-0740-1
