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Photosynthesis measurement on the Clusia minor tree. Under stressful conditions, this tree 'switches' to CAM photosynthesis. Under favourable conditions and with an adequate water supply, conventional \(\mathrm{C_3}\) photosynthesis takes place.
Photo Credit: © Gert Bachman
Scientific Frontline: Extended "At a Glance" Summary: Evolution of CAM Photosynthesis in the Clusia Genus
The Core Concept: Crassulacean Acid Metabolism (CAM) is a highly water-efficient form of photosynthesis where plants absorb carbon dioxide at night to minimize daytime evaporation. Recent genomic analysis of the tropical tree genus Clusia reveals that the extraordinary diversity of its CAM traits evolved through ancient genome duplications followed by millions of years of genetic restructuring.
Key Distinction/Mechanism: Unlike standard \(\mathrm{C_3}\) photosynthesis, where plants open their stomata to absorb \(\mathrm{CO_2}\) during the day, CAM plants keep stomata closed in sunlight, absorbing \(\mathrm{CO_2}\) nocturnally and chemically storing it as malic acid. In Clusia, this is not a static evolutionary event but a highly plastic adaptation, allowing related species to exhibit hybrid, stress-induced, or fully pronounced CAM responses based on targeted genomic rewiring.
Major Frameworks/Components:
- Polyploidization and Diploidization: The evolutionary process in which plant genomes are multiplied and subsequently restructured over extended periods, causing redundant gene copies to be lost, deactivated, or repurposed for new functions.
- Metabolic Rewiring: The specific genetic modifications affecting the biological pathways responsible for nocturnal \(\mathrm{CO_2}\)storage, starch breakdown, and cellular energy supply.
- Phenotypic Plasticity: The ability of genetically related species (Clusia rosea, C. minor, and C. major) to express fundamentally different photosynthetic strategies to survive in diverse ecological niches and stress conditions.
Branch of Science: Genomics, Evolutionary Biology, Plant Physiology, and Molecular Systems Biology.
Future Application: The newly mapped genomic data identifying efficient \(\mathrm{CO_2}\) fixation and high water-use mechanisms can serve as a vital blueprint for bioengineering drought-resistant agricultural crops.
Why It Matters: As global temperatures rise and water becomes increasingly scarce, understanding the genetic foundation of water-saving photosynthesis provides critical insights for adapting vulnerable food systems to arid, climate-stressed environments.
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| Clusia in the Monteverde cloud forest, Costa Rica. Photo Credit: © Wolfram Weckwerth |
Through photosynthesis, plants use sunlight to convert water and carbon dioxide into energy-rich sugars and oxygen. Drought presents a major challenge to this process. A research team led by Wolfram Weckwerth at the University of Vienna has now demonstrated how a particularly water-efficient variant of this process (CAM) has evolved in diverse ways within a single tropical tree genus. By analyzing the genomes of three species of the genus Clusia, the researchers were able to trace how genome duplication and subsequent genetic rearrangement contribute to the diversity of different CAM traits. The findings have recently been published in Nature Communications.
Around 1800, Alexander von Humboldt made an unusual observation. He dipped the leaf of a tropical tree into water and noted that, despite the sunlight, no oxygen bubbles formed—as had previously been the case. This plant keeps its stomata—which normally serve to absorb \(\mathrm{CO_2}\) and release oxygen during the day—closed during daylight hours, thereby preventing water loss through evaporation. \(\mathrm{CO_2}\) is then absorbed at night, chemically bound, and stored in the form of malic acid. This principle is known as "CAM photosynthesis" (crassulacean acid metabolism). How this strategy has evolved within the genus Clusia and why it occurs in different forms have, until now, been poorly understood.
About the Study As part of the study, the genomes of three Clusia species representing different CAM phenotypes were analyzed: Clusia rosea, Clusia minor, and Clusia major. The research team combined molecular data with physiological measurements under realistic environmental conditions.
From Genomes to Photosynthesis The genus Clusia comprises the only known trees that practice CAM, and it exhibits an extraordinary range of photosynthetic strategies—from classical \(\mathrm{C_3}\) photosynthesis, in which plants absorb carbon dioxide during the day, to highly pronounced CAM. This diversity makes these trees an ideal research model for evolutionary transitions between different forms of photosynthesis. The analyses showed that all three Clusia species are ancient polyploids—their genomes were multiplied over the course of evolution (polyploidization) and subsequently restructured over long periods of time (diploidization). "In the process, gene copies are lost, deactivated, or assume new functions," explains lead author Hannes Kramml of the Division of Molecular Systems Biology, Department of Functional and Evolutionary Ecology, at the University of Vienna. Second lead author Johannes Herpell adds, "Genes crucial for nocturnal \(\mathrm{CO_2}\) storage in CAM metabolism are particularly affected." Study leader Wolfram Weckwerth goes on to explain, "The genomes have not simply multiplied; over millions of years, they have been reorganized, reduced, and functionally rewired. This enormous plasticity explains the physiological diversity of CAM in the genus Clusia."
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| Flower of Clusia grandiflora. The unusual resin of these flowers magically attracts bees. Photo Credit: © Wolfram Weckwerth |
CAM Under Realistic Environmental Conditions To investigate the effects of these genetic differences, the team analyzed the plants throughout the day under near-natural greenhouse conditions with varying water availability. They combined physiological measurements with analyses of gene activity, proteins, and metabolic products. Clusia rosea exhibits strong CAM with pronounced nocturnal storage of carbon dioxide in the form of malic acid. Clusia minor activates CAM primarily under stress conditions, while Clusia major displays a hybrid form of \(\mathrm{C_3}\) photosynthesis and CAM. These differences are consistently reflected in gene activity and metabolic profiles and can be linked to the newly identified genetic changes. Here, CAM does not appear as a singular evolutionary event but as the result of repeated genomic reorganization, which enabled the species to adapt to very different ecological niches.
Implications for Agriculture and Climate Resilience CAM plants require significantly less water and are, therefore, considered potential models for climate-resilient crops. The new genomic data enable the identification of metabolic processes associated with efficient \(\mathrm{CO_2}\) fixation and high water-use efficiency. In the long term, these findings could help adapt crops more specifically to arid environmental conditions.
Published in journal: Nature Communications
Title: Clusia genomes shed light on the evolution and diversity of crassulacean acid metabolism physiotypes
Authors: Hannes M. Kramml, Johannes B. Herpell, Clara Priemer, Zoe Wessely, Florian Schindler, Andreas Berger, Maximilian Kellner, Stefan Plott, Ágnes Dohovits, Tamara Schmidt, Peter Kerpan, Leila Afjehi-Sadat, Palak Chaturvedi, Arindam Ghatak, Martin Brenner, Iro Pierides, Lena Fragner, Eva M. Temsch, Fabio Trevisan, Menriti Ibrahim, Felix Fromwald, Anke Bellaire, Oleg Simakov, Werner Huber, Ulrich Lüttge, Ovidiu Paun, Susann Wicke, Hanna Weiss-Schneeweiss, Gert Bachmann and Wolfram Weckwerth
Source/Credit: Universität Wien
Reference Number: geno050526_01