For ages we have heard that plants have a trick for staying alive as they take in sunlight, water, and carbon dioxide, then turn it all into sugar and oxygen through photosynthesis. This system has worked for millions of years. It has serious trouble when water becomes scarce. Now a group led by Wolfram Weckwerth at the University of Vienna has discovered something about how a very water‑thrifty form of photosynthesis evolved. This form of photosynthesis did not appear once; it appeared again and again within a single group of tropical trees. The findings, published in Nature Communications, trace the story back to a genetic event that reshaped how these plants breathe.
A 200-year-old puzzle The mystery goes back to around 1800, when explorer and naturalist Alexander von Humboldt made an observation while studying a tropical tree. He dropped one of these tree leaves into water, expecting to see the usual stream of oxygen bubbles rise in sunlight. Nothing happened. It turned out the tree was on a different daily rhythm. The stomata. Pores that plants normally use to absorb CO₂ and release oxygen. Stay shut during daylight hours to stop water from evaporating. Instead, the tree absorbs CO₂ at night, turns it into acid and stores it until sunrise. This strategy is called CAM photosynthesis, for Crassulacean Acid Metabolism. Scientists have known the mechanics of CAM for a long time. What has stayed unclear is how this unusual system first evolved within the tree genus Clusia and why different species in that same genus rely on CAM so differently. Comparing three trees To investigate this question, the research group compared the genomes of three Clusia species: Clusia rosea, Clusia minor, and Clusia major. Each species uses CAM to a degree, and the research group paired this genetic work with physiological measurements taken in realistic environmental conditions. Clusia turns out to be a valuable genus for this type of research. It is the known group of trees that uses CAM and its species cover a huge range of photosynthetic strategies. From normal daytime carbon absorption (C3 photosynthesis) all the way to intense, full‑blown CAM. That range lets scientists study, within one family tree, how plants shift between different ways of surviving. An ancient genome duplication changed everything
The genetic analysis showed that all three species share an ancestral event: their genomes were duplicated at some point deep in their evolutionary history and then gradually reorganized and reduced over millions of years. A process scientists call diploidization.
As per Hannes Kramml, the lead author of the study from the University of Vienna’s Division of Molecular Systems Biology and the co‑lead author, Johannes Herpell, the process of gene copies being lost, deactivated, or taking on functions. They further added that the genes store carbon dioxide at night were especially affected by this reshuffling. In words, the trees did not just end up with duplicate copies of the same genetic toolkit. That extra genetic material was slowly turned into something new. Another expert of the study, Weckwerth, the genomes have not simply multiplied; over millions of years they have been reorganized, reduced, and functionally rewired. That flexibility helps explain why CAM looks so different from one Clusia species to the next. Three trees, three strategies When the research group watched the trees directly. Tracking their behavior all day under different water conditions. The differences were striking. Clusia rosea relies heavily on CAM storing amounts of carbon dioxide overnight. Clusia minor mostly keeps its photosynthesis running and only switches to CAM when conditions become stressful. Clusia major splits the difference by running a system that mixes daytime C3 photosynthesis with nighttime CAM. These behavioral differences matched what the research group saw at the level matching patterns of gene activity, protein production, and metabolism. Taken together, the evidence suggests CAM did not arise from an evolutionary jump. Instead, repeated rounds of genome reorganization appear to have produced versions of this water‑saving strategy, each fine‑tuned to help different species cope with different environments. You use AI every day. Now get your AI Quotient. Take the AIQ test Get the latest Lifestyle News and more. Download the TOI app.