Scientists have edited the chloroplast-encoded Rubisco large subunit in Arabidopsis, increasing Rubisco turnover, photosynthesis and plant growth. Here is what this 2026 breakthrough really means for crop improvement.

Can One Amino-Acid Change Really Improve Photosynthesis?

For decades, plant scientists have faced a fascinating problem.

Plants depend on one enzyme for the entry of atmospheric carbon dioxide into the Calvin–Benson cycle: ribulose-1,5-bisphosphate carboxylase/oxygenase, better known as Rubisco.

Rubisco is essential for life as we know it. Yet from an engineering perspective, it is far from an ideal enzyme.

It fixes CO₂ relatively slowly and cannot perfectly distinguish carbon dioxide from oxygen. When Rubisco reacts with O₂ instead of CO₂, it initiates photorespiration, which reduces the efficiency of net carbon assimilation.

For this reason, scientists have spent decades asking:

Can we build a better Rubisco?

A study published in Nature Communications on 19 June 2026 provides an important new answer.

Wataru Yamori and colleagues used chloroplast genome editing to modify the rbcL gene of Arabidopsis thaliana. Two single amino-acid substitutions—M309I and D397N—increased Rubisco’s catalytic turnover rate without reducing Rubisco abundance.

More importantly, these biochemical changes translated into higher photosynthetic CO₂ assimilation and greater plant growth under specific experimental conditions.

The study therefore connected an unusually complete chain of events:

Chloroplast DNA editing → altered Rubisco → altered enzyme kinetics → increased photosynthesis → increased plant biomass

That is what makes this study particularly exciting.

Key Findings at a Glance

Finding	Result
Plant studied	Arabidopsis thaliana
Gene edited	rbcL
Genome	Chloroplast
Main beneficial substitutions	M309I and D397N
Rubisco catalytic turnover, kcat	Increased
Rubisco abundance	Comparable to wild type
CO₂ assimilation at 400 µmol mol⁻¹ CO₂	Increased
Stomatal conductance	Comparable to wild type
Intrinsic water-use efficiency	Increased under measurement conditions
Growth at low CO₂	No significant advantage
Growth at 381 and 549 µmol mol⁻¹ CO₂	Increased
90-day cultivation	Greater shoot, root and harvested seed biomass
Elevated CO₂ + 25°C	Growth advantage retained
Elevated CO₂ + 30°C	Advantage disappeared
Tested in food crops?	Not in this study

First, What Exactly Does Rubisco Do?

Rubisco catalyses the carboxylation of ribulose-1,5-bisphosphate (RuBP) during the Calvin–Benson cycle.

The productive reaction can be simplified as:

RuBP + CO₂ → unstable six-carbon intermediate → two molecules of 3-phosphoglycerate (3-PGA)

These molecules subsequently enter the reduction and regeneration phases of the Calvin–Benson cycle, ultimately supporting carbohydrate production and the synthesis of many other organic compounds required for plant growth.

Rubisco therefore sits at a critical gateway through which inorganic atmospheric carbon enters biological metabolism.

In higher plants, the predominant form of Rubisco is an L₈S₈ complex consisting of eight large subunits and eight small subunits.

The large subunits contain the catalytic sites and are encoded by the rbcL gene in the chloroplast genome.

The small subunits are encoded primarily by nuclear RBCS genes, synthesized outside the chloroplast and subsequently imported into it.

This split genetic architecture is one reason engineering plant Rubisco is technically challenging.

Why Is Rubisco Considered Inefficient?

Calling Rubisco a “bad enzyme” is too simplistic.

Rubisco has evolved for billions of years under changing atmospheric and cellular environments. Its current properties represent evolutionary compromises.

Nevertheless, several characteristics limit photosynthetic efficiency in modern C₃ plants.

1. Rubisco is relatively slow

Plant Rubisco does not process CO₂ at the extraordinary catalytic rates achieved by many other metabolic enzymes.

Plants compensate partly by producing large quantities of it.

Rubisco can therefore represent a substantial proportion of soluble leaf protein, making it a major investment of leaf nitrogen.

A faster or otherwise more efficient Rubisco could potentially allow plants to obtain more carbon assimilation from the enzyme they already possess.

2. Rubisco also reacts with oxygen

Rubisco is both a carboxylase and an oxygenase.

During carboxylation:

RuBP + CO₂ → two 3-PGA

During oxygenation:

RuBP + O₂ → one 3-PGA + one 2-phosphoglycolate

The 2-phosphoglycolate cannot simply continue through the Calvin–Benson cycle.

Instead, it must be recycled through photorespiration, a pathway involving chloroplasts, peroxisomes and mitochondria.

This process consumes energy and releases some previously fixed CO₂.

3. Faster Rubisco is not automatically better

This is one of the most important concepts in Rubisco engineering.

Rubisco performance involves trade-offs among properties including:

• catalytic turnover rate (kcat)
• apparent CO₂ affinity (Kc)
• carboxylation efficiency (kcat/Kc)
• CO₂/O₂ specificity (Sc/o)

Increasing one characteristic does not guarantee improvement in all the others.

A faster Rubisco, for example, may discriminate less effectively between CO₂ and O₂.

So the goal is not simply to make Rubisco faster.

The goal is to produce a Rubisco whose kinetic properties are advantageous inside a living plant under the environmental conditions in which that plant grows.

What Did the Researchers Actually Edit?

Instead of replacing plant Rubisco with an enzyme from another organism, the researchers introduced precise substitutions into the native Arabidopsis Rubisco large subunit.

The study initially focused on six candidate substitutions suggested by previous Rubisco research:

• M309I
• L74M
• I393M
• D397N
• A414T
• P415A

Because the chloroplast base editor used in the experiment produces particular nucleotide conversions, some resulting amino-acid changes differed from the candidate substitutions. For example, editing produced L74F and P415S at those targets.

The researchers also recovered several unintended editing products.

Among the resulting collection of Rubisco-edited plants, two substitutions clearly stood out:

M309I

At residue 309:

Methionine (M) → Isoleucine (I)

D397N

At residue 397:

Aspartic acid (D) → Asparagine (N)

Both increased Rubisco catalytic turnover.

But most of the other edited variants did not produce the same beneficial combination of enzyme and plant-level effects.

This is an important reminder:

Rubisco cannot simply be improved by making arbitrary amino-acid changes.

Why Was M309I Particularly Interesting?

M309I was not chosen randomly.

Previous work in Flaveria—a genus containing both C₃ and C₄ species—had implicated position 309 in differences in Rubisco kinetics.

The 2026 study also examined Rubisco sequences across numerous plant species.

Unlike several highly conserved positions, residue 309 shows natural variation: both methionine and isoleucine occur in plants.

M309I therefore partly explores catalytic variation that evolution itself has already sampled.

D397N presents a different story.

Why Is D397N So Interesting?

The researchers found D397 to be highly conserved across the plant species they examined.

D397N had previously emerged from Rubisco mutation screening involving cyanobacterial Rubisco, but what the substitution would do by itself in a higher-plant Rubisco was less clear.

In the Arabidopsis experiment, D397N significantly increased kcat.

It also reduced CO₂/O₂ specificity.

In the statistical comparisons reported in the Results, Kc and kcat/Kc were comparable to wild type. The authors nevertheless noted in their Discussion that the numerical direction of these parameters suggested a potentially favourable catalytic balance.

This makes D397N especially interesting for future testing.

It also raises an evolutionary question:

If D397N can be beneficial, why is D397 so strongly conserved in plants?

How Did Scientists Edit a Chloroplast Gene?

Editing rbcL is considerably more difficult than editing an ordinary nuclear gene because rbcL resides in the chloroplast genome.

Plant cells can contain many chloroplasts, and chloroplasts contain multiple copies of their genome.

For a stable chloroplast mutation, researchers ideally want the edited sequence to dominate the plastid genome population—a condition known as homoplasmy.

Conventional CRISPR approaches also face difficulties in chloroplasts, particularly because efficiently delivering guide RNAs into chloroplasts remains challenging.

The researchers instead used a targeted chloroplast base-editing system called ptpTALECD.

For M309I, which could not be generated with the original editor, they used ptpTALECD_v2mod, containing a cytidine deaminase domain with greater base-editing activity.

The researchers subsequently selected null-segregant plants that retained the desired chloroplast mutation but no longer carried the nuclear T-DNA encoding the editing machinery.

This allowed stable, homoplasmic rbcL mutations to be analysed.

What About Off-Target Mutations?

The researchers investigated possible off-target changes in the chloroplast and mitochondrial genomes of selected M309I and D397N lines using next-generation sequencing.

No off-target mutations were detected in three of the four analysed lines.

One M309I line contained a C-to-T substitution in an intergenic region 65 base pairs upstream of rpoB, which the researchers considered unlikely to have a functional effect.

This does not prove that every conceivable off-target effect is impossible.

However, it provides useful evidence for relatively high organellar-genome specificity in the lines examined.

The Key Biochemical Result: Rubisco Became Faster

The researchers measured the kinetic properties of Rubisco isolated from the edited plants.

Both M309I and D397N showed significantly higher catalytic turnover rates (kcat) than wild-type Col-0 Rubisco.

But their other kinetic properties reveal why Rubisco engineering is complicated.

M309I: faster, but with trade-offs

Compared with wild type, M309I showed:

• higher kcat
• higher Kc
• lower kcat/Kc
• lower Sc/o

A higher Kc indicates poorer apparent affinity for CO₂.

A lower Sc/o indicates reduced discrimination between CO₂ and O₂.

M309I therefore became faster while some other kinetic properties shifted in an unfavourable direction.

Yet under the relevant growth conditions, its overall physiological effect was still positive.

D397N: a different kinetic balance

D397N showed:

• significantly higher kcat
• lower Sc/o
• Kc statistically comparable with wild type
• kcat/Kc statistically comparable with wild type

The results therefore illustrate something fundamental:

There is no single number that tells us whether a Rubisco is “better.”

The entire kinetic profile has to be considered within the physiological environment of the plant.

The Plants Did Not Simply Make More Rubisco

This is an important control.

M309I and D397N plants contained Rubisco amounts comparable to wild-type Col-0.

Their total chlorophyll content was also comparable with wild type.

The researchers additionally detected no significant differences in Rubisco activase abundance or Rubisco activation state among Col-0, M309I and D397N.

So the improved photosynthesis cannot simply be explained by the edited plants producing more Rubisco.

Instead, the evidence points to changes in Rubisco catalytic behaviour itself.

Did Photosynthesis Actually Increase?

Yes—but the environmental conditions matter.

At 400 µmol mol⁻¹ CO₂, M309I and D397N plants showed significantly higher net CO₂ assimilation than wild-type Col-0.

They also showed significantly higher photosystem II electron transport rates and tended to have lower non-photochemical quenching.

Importantly, stomatal conductance and intercellular CO₂ concentration remained comparable to wild type.

Therefore, the higher assimilation rate was not simply the result of wider stomatal opening and greater CO₂ supply.

The evidence instead supports an internal biochemical improvement in photosynthetic carbon assimilation.

Intrinsic Water-Use Efficiency Also Increased

Because assimilation increased while stomatal conductance remained comparable, the ratio:

A / gs

also increased.

This ratio is known as intrinsic water-use efficiency (WUEi), where:

A = net CO₂ assimilation rate

and

gs = stomatal conductance

This is potentially valuable.

It suggests that under the measurement conditions, the edited plants gained more carbon per unit stomatal conductance.

However, this result should be interpreted carefully.

Higher leaf-level WUEi does not prove improved whole-season water-use efficiency or drought tolerance.

Those questions require additional whole-plant and field experiments.

What Happened at Very High CO₂?

The advantage was not unlimited.

As CO₂ concentration increased to around 1,200 µmol mol⁻¹, most significant differences in photosynthetic performance between M309I/D397N and wild type disappeared.

This makes physiological sense.

Photosynthesis is controlled by several interacting limitations.

At moderate CO₂, Rubisco carboxylation can exert substantial control over photosynthesis.

At higher CO₂, limitation can shift toward processes such as:

• RuBP regeneration
• electron transport
• triose-phosphate utilisation

Once Rubisco is no longer the principal bottleneck, making Rubisco faster cannot indefinitely increase photosynthesis.

This leads to one of the most important lessons from the study:

Photosynthesis is a system, not a single enzyme.

Did Faster Rubisco Produce Larger Plants?

This is perhaps the most exciting result.

The researchers grew plants under three CO₂ environments:

Low CO₂: 286 µmol mol⁻¹
Ambient experimental CO₂: 381 µmol mol⁻¹
Elevated CO₂: 549 µmol mol⁻¹

At low CO₂, M309I and D397N did not significantly increase shoot dry weight or total leaf area compared with wild type.

At ambient and elevated CO₂, however, both substitutions produced significantly greater total leaf area and shoot dry weight at 48 days after sowing.

Interestingly, these differences were not significant during earlier growth measurements.

The advantage emerged later.

That suggests relatively modest improvements in carbon assimilation may accumulate over time until they become measurable differences in biomass.

The Advantage Continued Later in Development

The researchers also conducted longer cultivation experiments at ambient experimental CO₂.

Across a 90-day cultivation, M309I and D397N plants showed greater growth than wild type.

They produced higher:

• shoot dry weight
• root dry weight
• harvested seed weight

The seed result is especially interesting because agricultural productivity ultimately depends on harvestable products rather than leaf photosynthesis alone.

But an important distinction remains:

Greater seed biomass in Arabidopsis is not proof of greater grain yield in wheat or rice.

That must be tested directly in crop species.

What Happened at Higher Temperature?

This part of the experiment provides an important warning against overhyping the results.

Under elevated CO₂ and 25°C, M309I and D397N still produced significantly greater growth than wild type.

At 30°C, however, their growth became comparable with Col-0.

The growth advantage disappeared.

This means these substitutions should not currently be described as heat-tolerant Rubisco mutations.

Several processes could potentially contribute to the loss of advantage at higher temperature, including increased photorespiration and limitations elsewhere in photosynthesis and metabolism.

But the experiment did not establish one definitive mechanism.

What it does establish is that:

A Rubisco modification beneficial under one environment may not retain that benefit under another.

How Can Mutations Far from the Active Site Change Catalysis?

One of the most fascinating aspects of the study came from structural analysis.

Neither M309 nor D397 sits directly within Rubisco’s catalytic active site.

The researchers therefore used cryo-electron microscopy (cryo-EM) to examine the structure of wild-type, M309I and D397N Rubisco.

They observed structural alterations involving the 60s loop, around residues 64–67.

Rubisco contains flexible loops whose movements are involved in the catalytic cycle.

The 60s loop and loop 6 participate in structural rearrangements associated with catalysis.

The M309I and D397N substitutions altered structural behaviour in this region despite being located far away.

The authors proposed that altered 60s-loop dynamics may contribute to the increased catalytic turnover.

However, this remains a mechanistic hypothesis, rather than a completely established molecular explanation.

The structural observations show that the mutations changed Rubisco’s conformation, but exactly how those changes accelerate catalysis requires further investigation.

A Small Mutation Can Have a Long-Range Effect

This result carries a broader lesson for protein engineering.

Enzymes are not rigid structures.

They are dynamic three-dimensional molecular machines.

Changing one amino acid can influence:

• protein packing
• subunit interactions
• loop flexibility
• conformational transitions
• catalytic behaviour at a distant site

Future Rubisco engineering may therefore need to look beyond residues that directly contact the substrate.

M309I and D397N demonstrate that potentially useful catalytic changes can arise from modifications far from the active site.

Why Has Evolution Not Already Produced the Perfect Rubisco?

Because evolution does not optimise an isolated enzyme for maximum laboratory performance.

A Rubisco variant must function across changing:

• CO₂ concentrations
• O₂ concentrations
• temperatures
• light environments
• developmental stages
• water availability
• nutrient conditions

A mutation that increases turnover might simultaneously reduce specificity.

A variant that works well under elevated CO₂ may perform poorly under CO₂ limitation.

A mutation that succeeds at 25°C may lose its advantage at 30°C.

Rubisco therefore represents an evolutionary compromise, rather than simply an inefficient enzyme that evolution somehow failed to optimise.

M309I demonstrates this beautifully.

It became faster, but its CO₂ affinity and CO₂/O₂ specificity became less favourable.

Nevertheless, the trade-off was beneficial under some of the conditions tested.

C₄ Plants Give Us an Important Clue

C₄ plants possess a carbon-concentrating mechanism that raises CO₂ around Rubisco.

This changes what constitutes an optimal Rubisco.

When Rubisco operates in a high-CO₂ environment, greater catalytic turnover can sometimes be advantageous even if CO₂/O₂ specificity is lower.

M309I is particularly interesting because variation at position 309 has previously been associated with kinetic differences among Flaveria species spanning C₃ and C₄ photosynthesis.

The broader lesson is important:

There may never be one universally perfect Rubisco.

Instead, future Rubisco engineering may need to optimise the enzyme for the species, CO₂ environment, temperature and photosynthetic system of the target crop.

Could These Mutations Work in Crops?

Potentially.

But this study does not demonstrate that yet.

The experiments were performed in Arabidopsis thaliana.

Major C₃ crops such as wheat, rice and soybean also rely heavily on Rubisco, so improving Rubisco remains highly relevant to agriculture.

But crop species differ in many ways, including:

• Rubisco sequence
• small-subunit composition
• canopy architecture
• source–sink relationships
• nitrogen allocation
• growth temperature
• reproductive development
• leaf lifespan

A mutation beneficial in Arabidopsis may therefore behave differently in another plant.

M309I also corresponds to natural variation already found among some plants.

D397, by contrast, was strongly conserved among the species examined in the study, making D397N an especially interesting candidate for broader experimental testing.

Before anyone can claim increased crop yield, however, these substitutions need to be tested directly in crops.

More Photosynthesis Does Not Automatically Mean More Yield

This distinction is crucial.

Crop yield depends on much more than leaf carbon fixation.

Additional photosynthate must be:

• exported from source leaves
• transported through the plant
• supported by adequate water and mineral nutrition
• incorporated into new biomass
• allocated to harvestable organs

If the plant lacks sufficient sink capacity, increasing photosynthesis may not translate proportionally into yield.

Therefore:

Higher Rubisco activity does not automatically mean higher photosynthesis.

And:

Higher photosynthesis does not automatically mean higher crop yield.

What makes the 2026 study particularly encouraging is that the effect did not stop at enzyme kinetics.

It progressed from altered Rubisco kinetics to greater photosynthesis, greater vegetative biomass and ultimately greater harvested seed biomass in Arabidopsis.

That is a stronger proof of concept than an enzyme-only improvement.

Could Rubisco Editing Improve Nitrogen-Use Efficiency?

Theoretically, perhaps—but the present study does not prove this.

Rubisco represents a substantial nitrogen investment in C₃ leaves.

A sufficiently faster Rubisco could theoretically allow a plant to achieve a particular photosynthetic rate using less Rubisco protein, potentially freeing nitrogen for other functions.

But that did not happen in this experiment.

M309I and D397N plants maintained approximately normal Rubisco abundance.

Therefore, claims that these particular plants already possess improved nitrogen-use efficiency would be premature.

Future research could investigate whether faster Rubisco can be combined with lower Rubisco abundance to achieve similar carbon assimilation with a smaller nitrogen investment.

Does This Mean the Plants Remove More CO₂ from the Atmosphere?

At the leaf level, increased net photosynthesis means more atmospheric CO₂ is incorporated into organic molecules during photosynthesis.

But this is not equivalent to proving long-term carbon sequestration.

For additional carbon fixation to contribute meaningfully to atmospheric carbon removal, that carbon would need to remain stored for substantial periods in pools such as:

• soil organic matter
• roots
• woody biomass
• durable harvested products

If the additional biomass is rapidly decomposed, consumed or respired, much of that carbon eventually returns to the atmosphere.

The experiment primarily demonstrates greater photosynthetic carbon assimilation and plant growth, not ecosystem-scale carbon sequestration.

Are These Plants GMOs?

The answer depends partly on regulatory definitions.

The researchers used genome-editing machinery to produce chloroplast mutations and subsequently selected null-segregant lines in which the editing T-DNA was absent while the chloroplast mutation remained.

The final plants could therefore retain a precise nucleotide change without retaining the editing construct.

Some regulatory systems distinguish certain genome-edited plants of this type from conventional transgenic organisms.

Others apply different definitions and regulatory frameworks.

The scientifically careful description is therefore:

These plants are genome edited. Whether an equivalent crop would legally be classified or regulated as a GMO depends on the jurisdiction.

Does Chloroplast Inheritance Reduce Gene Flow?

Potentially.

In many flowering plants, plastids are inherited predominantly through the maternal parent rather than pollen.

This can reduce the probability of chloroplast-encoded traits spreading through pollen.

But plastid inheritance is species dependent and is not universally exclusively maternal.

Therefore, it would be inaccurate to say chloroplast engineering completely prevents gene flow.

Rubisco Engineering Is Only One Part of the Photosynthesis Puzzle

Scientists are pursuing several complementary approaches to improve photosynthesis.

These include:

• engineering Rubisco kinetics
• introducing CO₂-concentrating mechanisms
• improving Rubisco activase
• engineering photorespiratory bypasses
• accelerating recovery from photoprotection
• optimising electron transport
• improving canopy photosynthesis
• altering carbon allocation

For example, previous work in tobacco demonstrated that engineered photorespiratory bypass pathways could increase plant productivity under field conditions.

Other researchers are investigating whether components resembling cyanobacterial carboxysomes or algal CO₂-concentrating systems can eventually be introduced into C₃ plants.

The future of photosynthetic engineering may therefore involve stacking several complementary improvements, rather than relying on a single “super enzyme.”

What Needs to Happen Next?

The next experiments will determine whether this discovery becomes agriculturally important.

Key questions include:

Can D397N improve Rubisco in rice?

What happens in wheat or soybean?

Will the advantage survive summer field temperatures?

How do these mutations perform under drought?

What happens under rapidly fluctuating sunlight?

Will increased photosynthesis translate into grain yield?

How do the mutations interact with different Rubisco small subunits?

Can Rubisco abundance eventually be reduced without sacrificing assimilation?

Are there developmental or reproductive penalties?

Does the effect remain stable across different genetic backgrounds and environments?

These are much harder tests than demonstrating increased photosynthesis in a controlled growth environment.

A crop canopy experiences continuously changing light, temperature, humidity and stomatal behaviour.

A useful engineered Rubisco must perform successfully in that complexity.

What the Study Proved — and What It Did Not

What the study demonstrated

The study showed that precise chloroplast editing of Arabidopsis rbcL can produce Rubisco variants with:

• increased catalytic turnover
• increased photosynthetic CO₂ assimilation under relevant measurement conditions
• increased intrinsic water-use efficiency at the leaf gas-exchange level
• increased leaf area and shoot biomass under ambient and elevated experimental CO₂
• increased shoot, root and harvested seed biomass during longer cultivation

What remains unproven

The study did not demonstrate:

• increased yield in wheat, rice or another major food crop
• drought tolerance
• heat tolerance
• improved whole-season crop water-use efficiency
• improved nitrogen-use efficiency
• universal benefits across environments
• ecosystem-scale carbon sequestration

Keeping these two categories separate is essential when interpreting the research.

Researcher’s Perspective: Why This Study Matters

The most important result is not simply that two groups of Arabidopsis plants became larger.

The deeper achievement is the proof of concept:

A precise change in chloroplast-encoded rbcL can modify native higher-plant Rubisco kinetics sufficiently to improve whole-leaf photosynthesis and ultimately plant growth.

Rubisco engineering has historically faced several major obstacles.

Scientists need to identify useful mutations.

The modified Rubisco must assemble and function properly inside higher-plant chloroplasts.

And improved enzyme kinetics must actually translate into better plant physiology.

This study brought all three together in one experimental system.

That is significant.

But it is not yet a crop revolution.

The experiments were performed in Arabidopsis.

The plants were grown under controlled conditions.

The benefits depended on environmental conditions.

The growth advantage disappeared at 30°C.

And both successful variants showed reduced CO₂/O₂ specificity.

Those limitations do not make the study less interesting.

Instead, they tell us exactly where the next experiments need to go.

Could This Lead to Faster-Growing Crops?

Possibly—but we do not know yet.

There are good reasons for optimism.

Researchers have now demonstrated:

precise chloroplast rbcL editing

↓

stable Rubisco amino-acid substitutions

↓

increased catalytic turnover

↓

greater photosynthetic CO₂ assimilation

↓

greater growth under particular conditions

↓

greater harvested seed biomass in Arabidopsis

That is a compelling biological chain.

But the decisive agricultural experiments are still ahead.

Until these mutations are tested across crop species and realistic field environments, they should be described as a promising proof of concept, not a finished crop technology.

The Bigger Lesson: Rubisco May Be More Engineerable Than We Thought

Rubisco has long been portrayed as an evolutionary compromise that is extraordinarily difficult to improve.

That remains largely true.

But this study suggests that the sequence found in modern plants is not necessarily the absolute biochemical optimum for every agricultural environment.

A single amino-acid substitution far from the active site altered Rubisco’s structural behaviour.

That alteration increased catalytic turnover.

And under the right physiological conditions, the improvement accumulated into greater plant growth.

This opens an intriguing possibility.

Instead of waiting for natural evolution to explore Rubisco sequence space, scientists may be able to accelerate that process using precision chloroplast genome editing.

Future agriculture may not rely on one universal “super Rubisco.”

Instead, researchers may eventually design Rubisco variants suited to:

• particular crop species
• different temperatures
• future atmospheric CO₂ concentrations
• controlled-environment agriculture
• C₃ or C₄ physiology
• engineered carbon-concentrating mechanisms

That future is not here yet.

But this 2026 study moves the idea one meaningful step closer to reality.

Frequently Asked Questions

What is Rubisco?

Rubisco—ribulose-1,5-bisphosphate carboxylase/oxygenase—is the enzyme responsible for incorporating CO₂ into RuBP during the Calvin–Benson cycle. It also catalyses a competing oxygenation reaction that initiates photorespiration.

What gene encodes Rubisco?

In higher plants, the Rubisco large subunit is encoded by the chloroplast rbcL gene. Rubisco small subunits are primarily encoded by nuclear RBCS genes.

Which mutations increased photosynthesis?

The two successful substitutions highlighted in the 2026 Arabidopsis study were M309I and D397N. Both significantly increased Rubisco catalytic turnover.

Did the plants simply produce more Rubisco?

No. Rubisco abundance in M309I and D397N was comparable to wild type. This supports altered catalytic performance, rather than Rubisco overproduction, as the central explanation.

Did the edited plants grow more?

Under the study’s ambient and elevated CO₂ treatments, M309I and D397N plants developed greater leaf area and shoot biomass by 48 days. Longer cultivation also produced greater shoot, root and harvested seed biomass.

No significant growth advantage was observed under the low-CO₂ treatment.

Did the mutations work at higher temperature?

At elevated CO₂ and 25°C, the edited plants retained a growth advantage.

At 30°C, their growth was comparable with wild type.

Therefore, the study does not demonstrate heat tolerance.

Have M309I and D397N been shown to increase yield in food crops?

Not in this study.

The reported experiments were conducted in Arabidopsis thaliana. Testing in rice, wheat, soybean and other crops remains necessary.

Does faster Rubisco always improve photosynthesis?

No.

Rubisco kinetics involve trade-offs among catalytic turnover, CO₂ affinity, catalytic efficiency and CO₂/O₂ specificity. Whether a faster enzyme benefits the plant depends on its complete kinetic profile and the surrounding physiological environment.

Can these mutations eliminate photorespiration?

No.

Both successful variants retained oxygenase activity, and their CO₂/O₂ specificity was lower than wild type.

Conclusion

The 2026 demonstration that precise chloroplast editing of rbcL can increase Rubisco catalytic turnover, photosynthetic CO₂ assimilation and Arabidopsis growth represents an important milestone in photosynthesis engineering.

Two single amino-acid substitutions—M309I and D397N—were sufficient to alter Rubisco kinetics without requiring an increase in Rubisco abundance.

Structural analysis further showed that these mutations, despite being located away from the catalytic site, altered the behaviour of a catalytic loop, providing an intriguing clue about how future Rubisco variants might be engineered.

But the experiment also demonstrates why photosynthetic engineering is difficult.

The modified Rubiscos retained kinetic trade-offs.

Their benefits depended on CO₂ availability.

The growth advantage disappeared at 30°C.

And increased crop yield from these mutations has not yet been demonstrated.

So perhaps the most interesting question is no longer:

Can Rubisco be improved?

Instead, it is:

Can scientists engineer the right Rubisco for the right crop and the right future environment?

For the first time, precision chloroplast genome editing is making that question increasingly testable.

Primary Research Discussed

Yamori, W., Nakazato, I., Qu, Y., et al. (2026). Chloroplast genome editing of Rubisco boosts photosynthesis and plant growth. Nature Communications, 17, 5066. DOI: 10.1038/s41467-026-73783-w

References and Further Reading

1. Yamori, W., Nakazato, I., Qu, Y., et al. (2026). Chloroplast genome editing of Rubisco boosts photosynthesis and plant growth. Nature Communications, 17, 5066. DOI: 10.1038/s41467-026-73783-w.

2. Lyu, J. (2026). Boosting Rubisco. Nature Plants, 12, 1304.

3. Nakazato, I., et al. (2021). Targeted base editing in the plastid genome of Arabidopsis thaliana. Nature Plants.

4. Prywes, N., et al. (2023). Rubisco function, evolution, and engineering. Annual Review of Biochemistry.

5. Zhao, L., et al. (2024). Engineering Rubisco to enhance CO₂ utilization.

6. South, P. F., et al. (2019). Synthetic glycolate metabolism pathways stimulate crop growth and productivity in the field. Science.

7. Chen, T., et al. (2023). Research on engineering bacterial-type Rubisco/carboxysome-related components in plant chloroplasts.

8. Bernacchi, C. J., et al. (2025). Safeguarding crop photosynthesis in a rapidly warming world. Science.