Photosynthetic hacks can boost crop yield, conserve water

Date:
August 10, 2020
Source:
Carl R. Woese Institute for Genomic Biology, University of Illinois
at Urbana-Champaign
Summary:
Plants are factories that manufacture yield from light and carbon
dioxide -- but parts of this complex process, called photosynthesis,
are hindered by a lack of raw materials and machinery. To optimize
production, scientists have resolved two major photosynthetic
bottlenecks to boost plant productivity by 27 percent in real-world
field conditions, according to a new study. This photosynthetic
hack has also been shown to conserve water.



FULL STORY ========================================================================== Plants are factories that manufacture yield from light and carbon
dioxide - - but parts of this complex process, called photosynthesis,
are hindered by a lack of raw materials and machinery. To optimize
production, scientists from the University of Essex have resolved
two major photosynthetic bottlenecks to boost plant productivity by
27 percent in real-world 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 steps that
are slower, and what we're doing is enabling these plants to build more machines to speed up these slower steps in photosynthesis." The RIPE
project is an international effort led by the University of Illinois to
develop more productive crops by improving 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 U.S. Foundation
for Food and Agriculture Research (FFAR), and the U.K. Government's
Department for International Development (DFID).

A factory's productivity decreases when supplies, transportation
channels, and reliable machinery are limited. To find out what limits photosynthesis, researchers have modeled each of the 170 steps of this
process to identify how plants could manufacture sugars more efficiently.

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

Inside two photosystems, sunlight is captured and turned 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, failing to shuttle electrons back and
forth efficiently.



==========================================================================
The team addressed 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 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 has improved a photosynthetic bottleneck
in the Calvin-Benson Cycle -- wherein carbon dioxide is fixed into
sugars -- by bulking up the amount of a key enzyme called SBPase,
borrowing the additional cellular machinery from another plant species
and cyanobacteria.

By adding "cellular forklifts" to shuttle electrons into the photosystems
and "cellular machinery" for the Calvin Cycle, the team also improved
the crop's water-use efficiency, or the ratio of biomass produced to
water lost by the plant.

"In our field trials, we discovered that these plants are using less water
to make more biomass," said principal investigator Christine Raines, a professor in the School of Life Sciences at Essex where she also serves
as the Pro-Vice- Chancellor for Research. "The mechanism responsible for
this additional improvement is not yet clear, but we are continuing to
explore this to help us understand why and how this works." These two improvements, when combined, have been shown to increase crop productivity
by 52 percent in the greenhouse. More importantly, this study showed up to
a 27 percent increase in crop growth in field trials, which is the true
test of any crop improvement -- demonstrating that these photosynthetic
hacks can boost crop production in real-world growing conditions.

"This study provides the exciting opportunity to potentially combine three confirmed and independent methods of achieving 20 percent increases in
crop productivity," said RIPE Director Stephen Long, Ikenberry Endowed University Chair of Crop Sciences and Plant Biology at the Carl R. Woese Institute for Genomic Biology at Illinois. "Our modeling suggests that
stacking this breakthrough with two previous discoveries from the RIPE
project could result in additive yield gains totaling as much as 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 project's second breakthrough,
also published in Science, created a shortcut in how plants deal with
a glitch in photosynthesis to boost 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 engineer, grow, and test -- to staple food crops
such as cassava, cowpea, maize, soybean and rice that are needed to feed
our growing population this century. The RIPE project and its sponsors are committed to ensuring Global Access and making the project's technologies available to the farmers who need them the most.


========================================================================== Story Source: Materials provided by Carl_R._Woese_Institute_for_Genomic_Biology,_University of_Illinois_at_Urbana-Champaign. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Patricia E. Lo'pez-Calcagno, Kenny L. Brown, Andrew J. Simkin,
Stuart J.

Fisk, Silvere Vialet-Chabrand, Tracy Lawson, and Christine
A. Raines.

Stimulating photosynthetic processes increases productivity
and water-use efficiency in the field. Nature Plants, 2020 DOI:
10.1038/s41477-020- 0740-1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200810113213.htm

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