Scientists have found several ways an unusual type of photosynthesis evolved. This discovery could help make crops better at surviving dry, hot weather.
Plants use sunlight, water, and carbon dioxide to create energy through photosynthesis. Drought makes this process much harder. A team at the University of Vienna, led by Wolfram Weckwerth, studied how a water-saving type of photosynthesis, called CAM, developed in a tropical tree genus.
They looked at the genes of three Clusia species. They found that their genomes duplicated and then changed over time. This led to many different CAM traits. Their findings were published in Nature Communications.
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Around 1800, Alexander von Humboldt noticed something odd. A tropical tree leaf in water did not produce oxygen bubbles in sunlight. This was different from other plants. This plant keeps its stomata, or leaf pores, closed during the day. Stomata usually take in CO2 and release oxygen in daylight.
Closing stomata reduces water loss. Instead, the plant takes in CO2 at night. It then stores it as malic acid. This process is called CAM photosynthesis (Crassulacean Acid Metabolism). Until now, scientists did not fully understand how this evolved in Clusia or why it has many forms.
The study analyzed the genomes of Clusia rosea, Clusia minor, and Clusia major. These species show different CAM traits. Researchers combined genetic data with measurements taken in real-world conditions.
The Clusia genus includes the only known trees that use CAM. It also shows a wide range of photosynthetic strategies. These range from standard C₃ photosynthesis, where plants take in CO2 during the day, to strong CAM.
This variety makes Clusia a good model for studying how photosynthesis types change over time. The analysis showed that all three Clusia species are ancient polyploids. This means their genomes multiplied during evolution and then changed over millions of years.
Hannes Kramml, a lead author, explained that gene copies are lost, turned off, or gain new functions. Johannes Herpell added that genes important for storing CO2 at night in CAM are especially affected.
Wolfram Weckwerth noted that the genomes did not just multiply. They were reorganized, reduced, and rewired over millions of years. This flexibility explains the many forms of CAM in Clusia.
CAM in Real-World Conditions
The team studied the plants in greenhouse conditions that mimicked nature, using different amounts of water. They measured plant physiology, gene activity, proteins, and metabolic products. Clusia rosea showed strong CAM, storing CO2 as malic acid at night.
Clusia minor mainly uses CAM when stressed. Clusia major uses a mix of C₃ photosynthesis and CAM. These differences match the genetic changes found in the study.
This suggests that CAM did not evolve just once. Instead, it emerged through repeated genome changes. This allowed different species to adapt to various environments.
Hope for Future Crops
CAM plants use much less water. This makes them good models for crops that need to survive hotter, drier climates. The new genetic data helps identify processes linked to efficient CO2 use and better water efficiency. These findings could help scientists adapt crops for dry conditions in the future.
Deep Dive & References
Clusia genomes shed light on the evolution and diversity of crassulacean acid metabolism physiotypes - Nature Communications, 2026
