New research from the University of Vienna reveals that tropical trees breathe at night thanks to ancient genome duplications. These duplications gave the trees an effective way to save water through a photosynthesis strategy that has endured for millions of years. The study shows how genetic reshuffling over time equipped these plants with a water-saving mechanism that could potentially be applied to developing drought-resistant crops.
The Night Breathing Strategy
Scientists studied three Clusia species to track how this kind of photosynthesis that saves water came about inside a single group of plants. The approach involves taking in carbon dioxide at night and storing it as malic acid, with the plant’s pores remaining shut during the hot daytime to keep water from escaping. It is called CAM photosynthesis, or Crassulacean Acid Metabolism.
The Clusia Comparison
Researchers examined the genetic material of three Clusia species, each showing a distinct type of CAM behavior: Clusia rosea, Clusia minor, and Clusia major. Their work brought together molecular information with observations of how the plants performed in settings that mirrored their natural environment.
Among the trees of the genus Clusia, the use of CAM is found nowhere else. That genus displays a broad array of photosynthetic methods, ranging from ordinary C3 photosynthesis all the way up to very strong CAM.
Ancient Genome Duplication
Genomic investigation showed that the genomes of all three Clusia species carry a deep history of multiplication. These genomes were enlarged through ancient duplication events, after which they underwent prolonged periods of reorganization and transformation.
Lead author Hannes Kramml, from the Division of Molecular Systems Biology within the Department of Functional and Evolutionary Ecology at the University of Vienna, is the one who explains “In the process, gene copies are lost, deactivated or take on new functions,”.
Second lead author Johannes Herpell adds: “Genes crucial for nocturnal CO2 storage in CAM metabolism are particularly affected.”
Rewiring the Genomes
“The genomes have not simply multiplied; over millions of years, they have been reorganized, reduced and functionally rewired,” study leader Wolfram Weckwerth explains. “This enormous plasticity explains the physiological diversity of CAM in the genus Clusia.”
In near natural greenhouse settings, the investigators watched over the trees across a full day while changing how much water they received. Their observations drew on both readings of plant physiology and studies of gene activity, proteins, and metabolic compounds.
Different Species, Different Approaches
The three species showed strikingly different approaches:
- Clusia rosea uses strong CAM and stores substantial amounts of carbon dioxide as malic acid during the night.
- Clusia minor mainly switches on CAM when it experiences stressful conditions.
- Clusia major uses a hybrid strategy combining C3 photosynthesis and CAM.
The patterns of gene activity and metabolism revealed those same physiological differences, giving the researchers a way to link the plants’ behavior with the genomic changes they found.
A Single Event, Multiple Outcomes
The results point to multiple separate events driving the development of CAM within Clusia, rather than one single evolutionary change. Instead, repeated rearrangements of the genome seem to have produced distinct variations on the water-conserving approach, aiding individual species in adapting to a wide range of environmental settings.
Beyond Tropical Trees
The findings may eventually carry weight beyond tropical trees. Plants that depend on CAM require substantially less water than those relying entirely on more conventional forms of photosynthesis. That quality makes them potentially useful models for breeding crops capable of surviving drought.
Newly available genomic data can be used to pinpoint metabolic pathways linked to efficient CO2 uptake and water conservation.
“This enormous plasticity explains the physiological diversity of CAM in the genus Clusia.”
Source material: “These tropical trees breathe at night to survive drought,” ScienceDaily.
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