Photosynthesis tips increase yield and conserve water

A team of scientists from the University of Essex increased crop productivity by 27 percent by solving two bottlenecks in photosynthesis – the process by which plants fix carbon dioxide in sugars that fuel growth cultures. Chidi Afamefule (left) holds an unmodified control factory while Kenny Brown (center) holds a modified factory to solve a bottleneck, and Patricia Lopez-Calcagno (right) holds a modified factory to solve two bottlenecks strangulation. Credit: RIPE Project / Claire Benjamin

Factories are factories that produce yield from light and carbon dioxide, but parts of this complex process, called photosynthesis, are hampered by a lack of raw materials and machinery. To optimize production, scientists at the University of Essex have solved two main photosynthetic bottlenecks to increase plant productivity by 27% under real field conditions, according to a new study published in Nature Plants. This is the third breakthrough of the Achieving Increased Photosynthetic Efficiency (RIPE) research project; however, this photosynthetic hack has also been shown to save water.

“Like a factory line, factories are as fast as their slower machines,” said Patricia Lopez-Calcagno, postdoctoral researcher at Essex, who led this work for the RIPE project. “We’ve identified some steps that are slower and what we’re doing is allowing these factories to build more machines to speed up those slower steps of photosynthesis.”

The RIPE project is an international effort led by the University of Illinois to grow more productive crops by enhancing photosynthesis – the natural, sunlight-powered process that all plants use to fix carbon dioxide into sugars that fuel growth, development and ultimately yield. RIPE is supported by the Bill & Melinda Gates Foundation, the Food and Agriculture Research Foundation of America (FFAR) and the UK Government’s Department for International Development (DFID).

A plant’s productivity declines when supplies, transport channels and reliable machinery are limited. To find out what limits photosynthesis, the researchers modeled each of the 170 steps in this process to identify how plants could make sugars more efficiently.

In this study, the team increased crop growth by 27% by solving two constraints: one in the first part of photosynthesis where plants convert light energy into chemical energy and the other in the second part. where carbon dioxide is fixed in sugars.

Inside two photosystems, sunlight is captured and transformed into chemical energy that can be used for other photosynthetic processes. A transport protein called plastocyanin moves electrons around the photosystem to fuel this process. But plastocyanin has a strong affinity for its acceptor protein in the photosystem, so it hangs out, failing to shuttle electrons efficiently.

The team solved this first bottleneck by helping plastocyanin share the load with the addition of cytochrome c6, a more efficient transport protein that has a similar function in algae. Plastocyanin needs copper, and cytochrome needs 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 fixed in sugars – by increasing the amount of a key enzyme called SBPase, by borrowing the additional cellular machinery of another plant species and cyanobacteria. .

By adding “cell forklifts” to transport electrons in photosystems and “cell machines” for the Calvin cycle, the team also improved the efficiency of culture water use, or the report. from the biomass produced to the water lost by the plant.

“In our field trials, we found that these plants use less water to produce more biomass,” said lead researcher Christine Raines, a professor at the School of Life Sciences in Essex, where she is also pro-vice-chancellor of research. . “The mechanism responsible for this further improvement is not yet clear, but we continue to explore it to help us understand why and how it works.”

2016 field trials conducted at the University of Illinois Energy Farm. Credit: Brian Stauffer / University of Illinois

These two improvements, when combined, have been shown to increase crop productivity by 52 percent in the greenhouse. More importantly, this study showed a 27 percent increase in crop growth in field trials, which is the real test of any crop improvement – demonstrating that these photosynthetic hacks can boost crop production under conditions. real growth.

“This study offers the exciting opportunity to potentially combine three proven and independent methods to achieve a 20 percent increase in crop productivity,” said Stephen Long, Director of RIPE, Ikenberry Endowed University Chair in Human Sciences. cultures and plant biology at the Carl R. Woese Institute for Genomics Biology in Illinois. “Our modeling suggests that combining this breakthrough with two previous findings from the RIPE project could result in additive yield gains of up to 50 to 60 percent in food crops.”

RIPE’s first discovery, published in Science, helped plants adapt to changing lighting conditions to increase yields by up to 20 percent. The second breakthrough of the project, also published in Science, created a shortcut on how plants deal with a photosynthesis problem to increase productivity by 20-40%.

Next, the team plans to translate these findings from tobacco – a model crop used in this study as a test bed for genetic improvements because it is easy to design, grow and test – to staple food crops such as cassava, cowpea, corn. , soybeans and rice which are needed to feed our growing population during this century. The RIPE project and its sponsors are committed to ensuring global access and making project technologies available to farmers who need them most.

Reference: “Stimulation of photosynthetic processes increases productivity and efficiency of water use in the field” by Patricia E. López-Calcagno, Kenny L. Brown, Andrew J. Simkin, Stuart J. Fisk, Silvere Vialet-Chabrand, Tracy Lawson and Christine A. Raines, August 10, 2020, Natural plants.
DOI: 10.1038 / s41477-020-0740-1