GM crops with improved photosynthesis to “end hunger”

Background

Photosynthesis is a series of biochemical reactions which enables plants to transform atmospheric carbon dioxide (CO2) into carbohydrates using sunlight, with oxygen as a byproduct. It provides the food and oxygen that sustains life on Earth.

Scientists have sought to understand photosynthesis for centuries. As knowledge has increased and technology has developed, this has led to an ambition to “optimise” the process to make it more efficient. This is based on the premise that despite millions of years of evolution, “only a fraction of the sunlight shining on a plant ends up fueling its growth”.¹⁸

Claims

Some scientists argue that to feed a growing population, “it is essential to enhance photosynthetic activities” ¹⁹ to increase carbon input into crops and thus increase yields. As far back as the 1970s, efforts to improve the efficiency of photosynthesis for food security through GM have received public attention. A Guardian article in 1977 cited a report from the US National Academy of Sciences as saying that “15 years of intensive research can alter photosynthesis to the point where agricultural yield will be doubled”.²⁰

Still today, the stated objective of the Gates-funded RIPE project is to “end hunger worldwide by improving the complex process of photosynthesis to increase crop production”. It claims: “By equipping farmers with higher-yielding crops, we can ensure that everyone has enough food to lead a healthy, productive life.” ²¹

According to RIPE, “If the ultra-photosynthetic plant is still far from having reached the fields, it is already flourishing in laboratories”.²²

Over the years, several high-profile media reported progress. A 2006 article in Science about the C4 Rice Project²³ reported hopes of “boosting yields by 50%”.  A 2014 Independent article – “GM crops as ‘as safe as conventional food’ and we need them, say scientists” – claimed that “improving photosynthesis [through GM] would boost crop yields and open the door to new sources of sustainable energy”.²⁴

In 2016, the BBC announced a “genetic breakthrough” in tobacco plants which, researchers said, could now be replicated “in rice, in soy bean and wheat.” ²⁵ In the following year, it celebrated a “new ‘super yield’ GM wheat”.²⁶

In a 2019 article, Bill Gates wrote that photosynthesis has “flaws” that need “fixing” and stated that the Bill & Melinda Gates Foundation, along with the US Foundation for Food and Agriculture Research and the UK Government’s Department for International Development, “is investing in the global effort to make photosynthesis more efficient” by genetically engineering plants.²⁷

In the same year scientists announced that they had engineered a new metabolic pathway in tobacco plants “that more efficiently recaptures the unproductive by-products of photosynthesis with less energy lost”, resulting in plants with 40% more biomass than those that had not been altered.²⁸ Reporting on the research, a Times article said, “If it can be made to work in food crops, billions more people could one day be fed without using any more of the Earth’s resources.” ²⁹ The Financial Times said the research could lead to “the next agricultural revolution, significantly boosting crop growth by making photosynthesis more efficient”.³⁰

In 2022 researchers announced an up to 33% increase in yield in soybean plants engineered for improved photosynthesis.³¹ The BBC headlined its article “Food crops made 20% more efficient at harnessing sunlight” and quoted lead researcher Prof Stephen Long as saying that this work was “the most important breakthrough” of his career and “contributes hugely to our ability to increase global food supply”.³² He was quoted in the Guardian as calling the findings “a spectacular result”, with Prof Jonathan Jones of the Sainsbury Laboratory commenting that “A soya bean breeder would spend an entire career trying to get that kind of increase in yield.” ³³

Although food security has been the main narrative around enhancing photosynthesis, it has also been claimed that enhancing photosynthesis can remove and store carbon dioxide from the atmosphere,² provide a sustainable source of biofuels,³ and even help manufacture chemicals.³⁴ 

Results

Photosynthesis is a complex process, comprised of approximately 170 interdependent steps.³⁵ It is dependent not just on light and carbon dioxide, but also on water, micronutrients, and nitrogen. Researchers admit that it “still holds many unanswered questions”.³⁶ This complexity likely lies at the heart of why there are not yet any commercially available GM crops with improved photosynthetic traits. As one group of researchers wrote, “single mutations or replacements of core photosynthetic proteins will not be probably enough to increase the photosynthetic performance owing to the multiple interactions of the photosynthetic machinery, which evolved over billions of years and is locked in a ‘frozen metabolic state’.’’ ³⁷ Another scientist cautioned that “large investments in attempts to make ‘better’ plants by improving basic physiological processes are not likely to succeed because natural selection has been optimizing these for millions of years”.³⁸

Even if efforts to enhance photosynthesis through GM approaches were to succeed, this may not increase crop yield.³⁹ In a review published in 2019, scientists stated: “Considerable research in the 1970s and 1980s showed that carbon input was not limiting for crop growth and yield. Instead, the availability and uptake of water and nutrients were found to be critical for increasing grain yield, and that conclusion still applies today.” They added, “by the early 1990s, it had become increasingly clear that increasing crop yield was not closely associated with rate of photosynthesis”.⁴⁰

Moreover, scientists have warned (in research unrelated to GM crops) that increasing carbon input into plants – an inevitable effect of increasing photosynthesis – reduces their nutritional value.⁴¹ This would undermine attempts to “feed the world” through GM photosynthesis-enhanced plants. In addition, higher photosynthesis rates could have important environmental trade-offs in the form of higher greenhouse gas emissions, as the plants would depend on more nitrogen fertiliser,⁴² a significant contributor to climate change. Between 23 and 31% of global nitrous oxide emissions come from production of nitrogen fertiliser and field emissions.⁴³

There are other issues to consider. A team of UK-based scientists emphasised that if improving photosynthesis is to succeed in increasing yields in real-life conditions, improvements will also be needed in nitrogen use efficiency and water use efficiency, as well as in responses to pests, diseases, and adverse weather and soil conditions.⁴⁴

Using genetic engineering approaches to achieve all or even one of these traits in any given crop is proving to be a huge challenge. In spite of these inherent problems, funding has been abundant in this area and a large number of research avenues are being explored by scientists hoping to genetically engineer photosynthesis. Some of the main ones are summarised below.

1. “Optimising” rubisco

Rubisco is the enzyme that fixes carbon dioxide from the air and transforms it into organic carbon, which the plant can use in photosynthesis and other processes. It is an ancient enzyme that evolved in an atmosphere with much more carbon dioxide and much less oxygen than the present day.⁴⁵ As a result it is said to be “remarkably inefficient”,⁴⁶ due to both its slow processing speed and its tendency to use oxygen instead of carbon dioxide more than 20% of the time.⁴⁷ This has made it a target for genetic engineers seeking to make photosynthesis more efficient at extracting carbon from the atmosphere.

In 1999, an article in Science reported, “Despite more than 20 years of effort [to engineer a better rubisco], the hopes have not yet paid off”. The article quoted T. John Andrews, a plant physiologist at the Australian National University, as calling rubisco “nearly the world’s worst, most incompetent enzyme” and “almost certainly the most inefficient enzyme in primary metabolism that there is”. He expressed hope that success in engineering a more efficient rubisco will be seen in “about 10 years”.⁴⁸

However, 45 years after research in this area began, no substantial gains have been reported. In 2023 scientists from the University of California, Berkeley, reviewed the performance of tobacco plants genetically engineered to express rubisco. They found that they “grow uniformly more slowly than wild type, even in chambers with CO₂ elevated to 1%… the cause of poor growth is clear, as rubisco expression levels are reduced by an order of magnitude compared to wild type.”

They reported, “Some improvements have been reported, but they are generally weak or else come with a trade-off”, with improvements in one function coming at the cost of another. They concluded, “Despite decades of research, the promises of rubisco engineering remain unrealised at every level.” ¹⁰

Most small gains that have been reported have occurred in non-food crops – mainly tobacco, due to its widespread use as a model experimental plant. Successes in tobacco may or may not be transferable to food crops. In 2014, a Nature editorial titled “Amped-up plants” reported that a group of scientists had managed to genetically engineer a tobacco plant to use rubisco from a bacterium, which is more efficient than the plant’s natural rubisco. The editorial quoted biologists as saying: “The work is a milestone on the road to boosting plant efficiency. The advance can be likened to having a new engine block in place in a high-performance car engine – now we just need the turbocharger fitted and tuned.” ⁴⁹

However, there is no sign yet of this happening. A 2022 paper summarised attempts to use synthetic biology (“synbio”) to engineer rubisco genes into photosynthetic microorganisms capable of sequestering atmospheric carbon dioxide: “While engineering RuBisCO remains an interesting target for improving carbon fixation, it has proven to be highly resistant to traditional engineering and decades of research would suggest that it is next to impossible to improve.” ⁵⁰

2. Relaxing photoprotection

Sunlight is essential for photosynthesis. However, the amount of light varies with time of day, season, weather, and the position of the leaf in the canopy. In addition, too much sunlight can damage the plant. Therefore, plants have evolved mechanisms to regulate their metabolic processes in response to the amount of light.⁵¹ Scientists often call this dynamic photosynthesis.⁵²

Researchers have suggested that some of these protective processes can inhibit efficient photosynthesis. For example, one of the mechanisms that plants use to deal with excess light – non-photochemical quenching (NPQ) – turns on rapidly at high light intensity but is slow to turn back off again when light becomes limited, such as when a cloud passes overhead.⁵³ Researchers aim to genetically engineer plants to fine tune these processes for greater photosynthetic efficiency.

However, this has proven difficult. In 2019 it was reported that “previous attempts to increase dynamic photosynthesis by overexpressing or removing a singular gene have not succeeded in enhancing plant biomass production”.⁵⁴ In addition, it has become clear that “processes involved in dynamic photosynthesis tightly interact with other physiological processes”,⁵² so more complex genetic changes would be required.

In 2022 researchers reported a success in the journal Science. They announced an up to 33% increase in yield in field trials of a soybean engineered for an accelerated switch back to full photosynthetic capacity when the light intensity reduces (for example, in shade).³¹ This finding was positively reported by the BBC,³² the Guardian,³³ and the New York Times.⁵⁵

These reports, however, failed to acknowledge the limitations of the research. Plant geneticist Dr Merritt Khaipho-Burch (now working with Corteva Agriscience) commented on Twitter/X that the paper announcing the results was “misleading”; that few plants were grown, making a small sample size; that the yields observed were “on the same level as state-wide trends”; that the “yield trials lacked sufficient replication to make any claims”; that a storm caused the GM plants to fall over (“lodge”), resulting in some lines yielding less than the untransformed “wild type” plants; and that the results were “only marginally significant”. She concluded: “Replication is key in science and unreplicated results make effects hard to believe.” ⁵⁶

Other critics included advocates of genetic engineering. Linus Blomqvist, former director of food and agriculture at the Breakthrough Institute,⁵⁷ cautioned: “If you see research that claims to have boosted a crop’s potential yield by more than like 10% it’s probably compared to a misleading baseline or only valid under very narrow conditions so it doesn’t translate to higher yields in the real world”.⁵⁸

A Twitter/X account identifying its main tweeter as Thomas Björkman, professor in the School of Integrative Plant Science at Cornell, blamed Science journal for misleadingly overstating the significance of the paper in its press release: “The yield claim… is, in my estimation, not puffery but misconduct in that it makes an improbable claim for which there is no evidence.” ⁵⁹

Guillaume Lobet, assistant professor at the Université catholique de Louvain in Belgium, blamed both the journal and the authors for the misleading coverage. He tweeted, “In addition to how science is *reported* (by third party media outlets), we also can reflect on how it is *advertised* in the first place… the ‘yield’ argument, that… might not be the strongest aspect of the paper… is highlighted on the cover of the journal, the title of the article, the journal highlight and in the paper abstract.” ⁶⁰

The New York Times, in an otherwise positive article on the research, cited unnamed sceptical scientists who commented, “If a process as fundamental as photosynthesis could be improved upon, then surely natural selection would have done so by now.” ⁵⁵

In response to the criticisms, one of the researchers, Steven Burgess, admitted the limitations of the study, stating, “This work is a proof of principle. There is a long way to go, and multi-site, multi-year comparisons are required before the exact impact on yield is determined.” ⁶¹

3. Engineering C4 photosynthesis

C4 photosynthesis is an evolutionary adaptation of the more common C3 photosynthesis. C3 refers to the fact that the first carbon compound the plant produces during photosynthesis contains three carbon atoms. However, in C3 photosynthesis, in high temperature and light conditions there is a tendency for oxygen instead of carbon dioxide to bind to the photosynthetic enzyme (a process known as photorespiration), which wastes the plant’s energy. In environments with high temperature and light, some plants – for example, maize and sugarcane – have evolved C4 photosynthesis, where an additional step of fixing carbon dioxide from the air by the enzyme PEP carboxylase reduces photorespiration, therefore increasing the efficiency of photosynthesis.

Scientists are attempting to genetically engineer C3 plants to use C4 photosynthesis. One project that has received international attention is the C4 Rice Project,²³ born out of a 2006 conference of the International Rice Research Institute (IRRI).⁶² An article in the journal Science at the time reported hopes of “boosting yields by 50%”. The article quotes IRRI crop scientist John Sheehy expressing hope that the research consortium “will be able to demonstrate that creating C4 rice is a real possibility by 2010”.⁶³

However, 14 years later, and despite the efforts of a global consortium of 11 labs with funding from the Bill & Melinda Gates Foundation,⁶⁴ scientists have not achieved this. The challenge is substantial, requiring a change in leaf anatomy and a transformation of several key regulatory genes simultaneously.⁶⁵ A 2023 review paper from the Project, then in its thirteenth year, highlighted “a number of unanswered questions”.⁶⁶

The European Union funded its own “3to4” project from 2012 to 2016, with a budget of $8.9m.⁶⁷ The project involved nine academic participants and five industrial participants, including Chemtex in Italy and Bayer CropScience.⁶⁸ The project reported some progress in understanding some of the pathways at play in C3 and C4 photosynthesis, which “provide a platform from which photosynthesis in rice can be improved in the future”.⁶⁹ However, the project did not have substantial results beyond this.

4. Capturing carbon

Recently there has been interest in altering photosynthesis in crops and trees so that they can absorb and store more carbon to mitigate climate change.

In 2023 the US-based start-up Living Carbon, which aims to produce “photosynthesis-enhanced trees” to grow faster and capture more carbon, received $21m in funding.⁷⁰ The company has reported a proof-of-concept success of 35–53% more biomass accumulated over four months of growth in a controlled environment.⁷¹ However, that has not yet been replicated in real-world conditions. Living Carbon is currently running a series of field trials, including a four-year trial with Oregon State University involving over 600 trees.⁷²

Also in 2023, the Guardian reported on the work of the Salk Institute for Biological Studies, which has been working to engineer crop plants they call “Salk Ideal Plants” since 2017. Current targets are soybeans, rice, wheat, corn, rapeseed/canola, sorghum and CoverCress (a strain of field pennycress).⁷³

Due to the boom in carbon credits, with companies wishing to offset their carbon emissions to reach their Net Zero targets, there is a great deal of funding available for this kind of research. The Salk’s funders include the Hess Corporation, an oil and gas exploration and production company, which gave $50 million.⁷⁴ However, despite this, scientists at the Salk have not yet succeeded in creating a plant which stores more carbon, and doubts have been raised about their ability to do so without affecting yield.⁷⁵

Another area of research is genetically engineering artificial photosynthesis systems – for example, in non-photosynthetic bacteria. Again, small proof-of-concept successes have been reported,⁷⁶ but nothing has yet been developed at scale.

Scaling up changes

So far, all published studies have been small-scale, although this fact is rarely highlighted in publicity reports. The challenges of scaling up changes to a whole field are substantial. A 2015 review concluded that “a central challenge to improving photosynthetic efficiency is knowing how alterations made to the photosynthetic process at the level of the chloroplast will scale to a whole canopy, whose complex seasonal development ultimately determines biomass production and yield”.⁷⁷

There are some examples of failed attempts to scale up lab or glasshouse results. For example, a project funded by the UK’s Biotechnology and Biological Sciences Research Council (BBSRC) from 2016–19 with £695,933 of public money attempted to improve the photosynthetic ability of wheat to increase yields. The scientists genetically engineered the wheat to have higher levels of the enzyme SBPase, which is involved in photosynthetic carbon dioxide assimilation. However, they reported that “although glass house data provided evidence that the over expression of SBPase would have a positive effect in the field – the field trial held at Rothamsted in 2019 showed no differences to wild type.” ⁷⁸

In 2023 a group of scientists warned in a Nature article titled, “Genetic modification can improve crop yields – but stop overselling it”, that “it is unlikely that more than a handful of genes with major beneficial effects on yield – in the absence of environmental stressors and pathogens – exist”. They go on to say that “none of the published studies claiming that a single gene or a few genes affect yield has been validated under conditions resembling those on farms”, and their publication in scientific journals is likely due to a lack of appropriate expertise in research teams and journal peer reviewers.⁷⁹

Biofuel and chemical production

In recent years interest has grown in biological chemical production as an alternative to traditional petrochemical-based synthesis. One of the ways this could potentially be achieved is through genetically engineering photosynthetic microorganisms to convert carbon dioxide into products such as long-chain alcohols, ethanol and hydrogen. These products could be used as biofuels or bioplastics, or as precursors to commodity chemicals.⁸⁰

However, scientists are experiencing many of the same difficulties with microorganisms as with plants. Notably, efforts to engineer a “better” rubisco by gene transfer (transgenesis) have not succeeded. This has led some researchers to propose using synthetic biology (redesigning organisms by assembling novel genomes to have new abilities) techniques to create new carbon fixation pathways, which “may prove to be a better methodology for the development of sustainable production hosts”. Yet these new pathways have had limited success in model organisms such as E. coli, and “it has yet to be shown if these pathways can function effectively in photosynthetic hosts”.⁵⁰ In addition, the production of chemicals from photosynthetic organisms has been demonstrated but large-scale production has not yet been shown to be possible.⁸¹

Research into producing biofuels from photosynthetic algae – initially naturally occurring strains but then increasingly GM – began in the 1970s and, according to a 2021 article, became a popular idea in the renewable energy industry from around 2009 to 2017. However, the hopes did not pan out: “After numerous setbacks, failed tests and enormous unanticipated production costs, algae biofuel today is no longer a firm favorite, with many companies dropping out of the race, including both Chevron and Shell.”

The article noted that key problems include the development of a strain of algae able to produce plentiful cheap fuel and scaling up. In addition, other alternative energy solutions, including wind and solar power, are outpacing algae biofuel advances. Big players like Shell and Chevron have abandoned the effort, though ExxonMobil continues work.⁸²

A 2021 review of attempts to produce biofuels from GM algae concluded that they were “still beset with many challenges”, including technical problems, disputes over patents on GM technologies, and health and environmental risks from accidental releases.⁸³

Artificial photosynthesis is a further area of interest for chemical and biofuel production. The companies Siemens and Evonik made headlines in 2019 when they announced the building of a test plant to create chemicals using carbon dioxide and water, powered by energy from renewables and bacteria. The project, which received €3.5m of funding from Germany’s Federal Ministry of Education and Research, was initially due to run until 2021.⁸⁴ However, there have been no updates since, suggesting that it was not commercially viable.

Companies

As the dream of enhancing photosynthesis is so vast and multifaceted, a large number of companies and academic research consortiums are involved, with the latter attracting external funding from various sources. For example, RIPE (Realising Increased Photosynthetic Efficiency), a project to engineer crops for enhanced photosynthesis led by the International Rice Research Institute (IRRI), began in 2012 with a five-year $25 million grant from the Bill & Melinda Gates Foundation.¹¹ Since that initial funding, the project has received a further $92 million from the Gates Foundation, as well as the Foundation for Food and Agriculture Research and the UK Foreign and Commonwealth Development Office.¹¹

Other organisations attempting to engineer crops and trees for more efficient photosynthesis include the startups Wild Bioscience,⁸⁵ a spin-off from Oxford University, and Living Carbon,¹³ with investors including Temasek and Toyota.⁸⁶

The EU has also funded projects in this space, including “3to4” from 2012–2016, with commercial partners including Bayer,¹⁴ and an ongoing five-year project called Photoboost.¹⁵

Patents

In a demonstration of the huge size of this field, a global patent search for “enhanced photosynthesis” returned 53,919 results (of which 27,851 are active).¹⁶ These include a patent on “Transgenic plants with increased photosynthesis and growth”, filed in 2017 by the Universities of Illinois and California,⁸⁷ on which Stephen Long, principal investigator of the RIPE consortium,¹⁸ holds inventor status.

Author: Ayms Mason. Review and editing: Claire Robinson, Franziska Achterberg. Scientific review: Prof Jack Heinemann.

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