Species of carnivorous bladderwort, butterwort and sundew plants harbor some of the smallest genomes found in flowering plants. Researchers have long wondered what genetic or environmental factors contribute to these miniature plant genomes and now, a team of scientists discovered that a single mutation correlates with and drives the downsizing of genomes across some carnivorous species within the Lentibulariaceae family. The results were recently published in Annals of Botany.
Mitochondria are the energy-producing organelles within cells. The researchers focused on a mutation in a gene called cytochrome c oxidase (COX), which codes for an enzyme critical for mitochondria to generate energy through cellular respiration. They hypothesized that the COX mutation boosts mitochondrial efficiency, providing an advantage for carnivorous plants that rely on suction traps to catch prey. However, the mutation may come at a cost by increasing production of damaging molecules called reactive oxygen species (ROS) as a byproduct of respiration.
To test this idea, the team based in Masaryk University compiled genome size data and chromosome measurements for over 100 species across the three genera that make up the carnivorous Lentibulariaceae family: Genlisea, Pinguicula and Utricularia. They also isolated and analyzed the sequence of the COX gene from each species to identify whether they carried the ancestral or mutated version. Using statistical analyses, the researchers assessed if patterns in the data supported the COX mutation driving smaller plant genomes over evolutionary time.
Their findings provide compelling evidence that the COX mutation contributes to genome downsizing in these carnivorous plants. Species with the mutated COX gene consistently had smaller genomes and chromosomes compared to those retaining the ancestral sequence. Phylogenetic modeling also revealed the genomes of COX mutation carriers trended towards becoming progressively smaller as an evolutionary response.
The researchers believe increased ROS levels resulting from the COX mutation overwhelm plants’ DNA repair abilities, leading to higher rates of genomic deletions over generations. As nonessential regions gradually removed, plant genomes shrink in size. While enhancing mitochondrial function benefits carnivorous traps, this genetic tweak comes at the cost of destabilizing the genome.
Our findings indicate that the whole genus Utricularia and sections Recurvatae and Genlisea from the genus Genlisea harbour CC or CS mutations in the COX gene… The observation that these Lentibulariaceae lineages tend to evolve smaller genome sizes compared to those with the ancestral LS state (genus Pinguicula, Genlisea section Tayloria) aligns with the hypothesis that changes in the COX sequence elevate ROS production, increasing DNA damage and fostering deletion-biased DNA repair, culminating in genome contraction.
By uncovering how a single mitochondrial mutation impacts genome evolution, this study sheds light on the complex genetic and environmental trade-offs shaping species. It illustrates how even subtle changes to cellular processes can cascade into altering an organism’s entire genome blueprint over evolutionary timescales. The work also highlights carnivorous plants as intriguing genetic models and underscores mitochondrial mutations as an underappreciated driver of genome change. Continued exploration of this unique system may reveal further unexpected findings.
READ THE ARTICLE
Zedek F., Šmerda J., Halasová A., Adamec L., Veleba A., Plačková K. and Bureš P. (2024) “The smallest angiosperm genomes may be the price for effective traps of bladderworts” Annals of Botany. Available at: https://doi.org/10.1093/aob/mcae107
