Human population can reach 9 billion by 2050, according to current projections. To answer the question “will there be enough food for that number”, farmers need to grow 50% more food on limited spaces.
So until today, plant scientists have been working to engineer crops with higher yields. One of the ways is improving photosynthesis.
Scientists have found that cyanobacteria (blue-green algae) are able to photosynthesize more effectively than most crops. Researchers have been trying to transfer that ability into crop plants, but this new study may propel that effort.
Photosynthesis and rubisco
Photosynthesis means that plants convert CO2, water, and light into oxygen and sucrose. Now, during this process, there’s an enzyme found in all plants that takes inorganic carbon from air and fixes or converts it to an organic form the plant uses to build tissues. It’s called Rubisco.
The thing is, rubisco reacts with both carbon dioxide and oxygen in the air. That can create toxic byproducts, slowing down photosynthesis and eventually lowering yields. In cyanobacteria, however, the rubisco is contained within microcompartments called carboxysomes that shield the Rubisco from oxygen.
Moreover, the carboxysome lets the cyanobacteria to concentrate carbon dioxidee. So, rubisco can use it for faster carbon fixation.
“Crop plants don’t have carboxysomes, so the idea is to eventually put in the entire carbon-concentrating mechanism from cyanobacteria into crop plants,” said the paper’s senior author Maureen Hanson.
To extract this system and make it work in crop plants, scientists must remove carbonic anhydrase from the chloroplasts. In simple English, the former is another naturally occurring enzyme, while the latter is substance in plant cells where photosynthesis happens.
They have to remove it because anhydrase’s role is to create an state of balance between CO2 and bicarbonate in plant cells. But, for this to happen in crops not cyanobacteria, bicarbonate in the system must reach levels many times higher than those found at equilibrium.
Hanson said, “So in this study, we did that step [of removing anhydrase] that’s going to be needed to make the carboxysome work.”
Current findings and future research
The authors used CRISPR/Cas9 gene-editing technology. It disables genes that express two carbonic anhydrase enzymes that are present in chloroplasts.
Before, another research team had used a different method to remove 99% of the anhydrase enzyme’s activity, and the plants grew normally. Alas, when Hanson and her colleagues removed 100% of the enzyme’s activity, the plants barely grew.
“It showed that plants need this enzyme to make bicarbonate that is used in pathways to make components of leaf tissue,” said Hanson.
When the scientists put the plants into a high CO2 growth chamber, they resumed normal growth. The high amounts of carbon dioxide led to a spontaneous reaction to form bicarbonate.
Because of this, the team believes that they’ve got a workaround to remove anhydrase and still have enough bicarbonate. In future research, they plan to improve what they’ve found now.
The scientists plan to make anhydrase unnecessary and get extra bicarbonate to improve photosynthesis.
According to the researchers, experiments showed that the absence of carbonic anhydrase did not interfere with photosynthesis.
There’s a bit of an issue about this discovery. Carbonic anhydrase found in chloroplasts is known to be involved in the plant’s defense pathways. But, Hanson’s group could manage to maintain the plant’s defense regardless.
Hanson said, “We now know we can make an inactive enzyme that won’t affect our carbon concentrating mechanism but will still allow the crop plants to be resistant to viruses.”
What about making plants adapt faster?
Finding out that we can improve photosynthesis to increase yield is no doubt a piece of good news. But what if there’s another alternative? What if we can bioengineer plants to adapt to, say, hotter climate?
Qualities of plant roots are vital to food supply in the future. That’s according to associate professor of plant biology at the University of Georgia, Alexander Bucksch.
Bucksch said, “When there is a problem in the world, humans can move. But what does the plant do? It says, ‘Let’s alter our genome to survive.’ It evolves.”
For a long time, farmers hadn’t had a thorough, good look about the root system of plants. Hence, they couldn’t make decisions about the optimal seeds to grow deep roots.
Published in Plant Physiology, the paper by Bucksch and colleagues introduced DIRT/3D (Digital Imaging of Root Traits). It’s an image-based 3D root phenotyping platform.
One of its abilities is measuring 18 architecture traits from mature field-grown maize root crowns excavated using the Shovelomics technique.
According to coauthor Jonathan Lynch, “This technology will make it easier to analyze and understand what roots are doing in real field environments, and therefore will make it easier to breed future crops to meet human needs.”
DIRT/3D itself is a 3-dimensional version of a previous 2D software that can obtain information about roots using a mobile phone camera. Since it first launched in 2016, this technology has been a useful tool for scientists worldwide, including researchers at leading agribusinesses.
So even though the bioengineering technology isn’t here yet, this is a great start towards its beginning. What the scientists have to focus on for now is getting the data.
Getting and assessing the data
The technology that the researchers used here may seem so simple. But the 3D scanner is also enabling basic science, addressing the problem of pre-selection bias because of sample limitations in plant biology.
Additionally, data collection takes only a few minutes, while the rig only costs a few thousand dollars to build, as opposed to half a million. That makes it scalable to perform high-throughput measurements of thousands of specimens.
Bucksch said, “Biologists primarily look at the one root structure that is most common—what we call the dominant root phenotype.
“But people forgot about all of the other phenotypes. They might have a function and a role to fulfill. But we just call it noise. Our system will look into that noise in 3D and see what functions these roots might have.”
It’s important to solve this food supply issue now so that we can solve potential problems in the future.
After all, the climate is changing. Farmers will get more challenges in the future like draughts, higher temperatures, low-soil fertility, and the need to grow food more sustainably.
If plant roots can adapt to these future challenges and conditions, that’ll make the pressure on food supply easier.
Bucksch said, “The potential, with DIRT/3D, is helping us live on a hotter planet and managing to have enough food.
“That is always the elephant in the room. There could be a point where this planet can’t produce enough food for everybody anymore, and I hope we, as a science community, can avoid this point by developing better drought adapted and CO2 sequestering plants.”