Plants have evolved several ways to use sunlight to turn water and carbon dioxide into energy-rich sugars and oxygen (photosynthesis). But when water becomes scarce, that process can become much more difficult. Researchers led by Wolfram Weckwerth at the University of Vienna have now uncovered how one especially water efficient form of photosynthesis (CAM) evolved in multiple ways within a single genus of tropical trees.
By comparing the genomes of three Clusia species, the team traced how ancient genome duplication followed by extensive genetic reorganization helped produce different forms of CAM. The findings were recently published in Nature Communications. A Photosynthesis Mystery Dating Back 200 Years Around 1800, Alexander von Humboldt noticed something unusual while studying a tropical tree.
He placed one of its leaves in water and found that, even in sunlight, it did not produce the oxygen bubbles he had observed before. The explanation lies in the plant's unusual daily schedule. Its stomata, the tiny pores that normally take in CO2 and release oxygen during the day, remain closed while the sun is up, reducing water loss through evaporation.
Instead, the plant absorbs CO2 at night, chemically binds it, and stores it as malic acid. This strategy is known as 'CAM photosynthesis' (Crassulacean Acid Metabolism). Although scientists have long known how CAM works, exactly how it evolved within the genus Clusia, and why different species use it in different ways, has remained unclear.
To investigate, the researchers analyzed the genomes of three Clusia species with different CAM phenotypes: Clusia rosea, Clusia minor, and Clusia major. They combined molecular data with measurements of how the plants functioned under realistic environmental conditions. The genus Clusia is particularly valuable for studying the evolution of photosynthesis because it contains the only known trees that use CAM.
Its species also display an unusually wide range of photosynthetic strategies, from conventional C3 photosynthesis, in which carbon dioxide is absorbed during the day, to very strong CAM. That diversity gives scientists a rare opportunity to examine how plants can transition between different forms of photosynthesis. Ancient Genome Duplication Rewired Photosynthesis The genomic analysis revealed that all three Clusia species are ancient polyploids.
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