How does a plant develop a taste for flesh? In the play Little Shop of Horrors, all it takes is a drop of human blood. But in real life, it takes much more. Now, a study of three closely related carnivorous plants suggests dextrous genetic shuffling helped them evolve the ability to catch and digest protein-rich meals.
Carnivorous plants have developed many devious ways to snare prey. Pitcher plants, for example, use “pitfall traps” that contain enzymes for digesting stray insects. Others—including the closely related Venus flytrap (Dionaea muscipula), the aquatic waterwheel plant (Aldrovanda vesiculosa), and the sundew (Drosera spatulata)—use moving traps. The sundew rolls up its sticky landing pad when mosquitoes get caught. And the Venus flytrap uses modified leaves, or pads, that snap shut when an insect lands—but only after the pads sense multiple touches on their trigger hairs.
To find out how these traps evolved, researchers led by computational evolutionary biologist Jörg Schultz and plant biologist Rainer Hedrich, both of the University of Würzburg, sequenced the genomes of the sundew, the aquatic waterwheel, and the Venus flytrap, which are all closely related. They then compared their genomes with those of nine other plants, including a carnivorous pitcher plant and noncarnivorous beetroot and papaya plants.
They found that the key to the evolution of meat eating in this part of the plant kingdom was the duplication of the entire genome in a common ancestor that lived about 60 million years ago, the team reports today in Current Biology. That duplication freed up copies of genes once used in roots, leaves, and sensory systems to detect and digest prey. For example, carnivorous plants repurposed copies of genes that help roots absorb nutrients, to absorb the nutrients in digested prey. “That root genes are being expressed in the leaves of carnivores is absolutely fascinating,” says Kenneth Cameron, a botanist at the University of Wisconsin, Madison.
Hedrich and his colleagues conclude that carnivory evolved once in the ancestor of the three species and, independently, in the pitcher plant. Adding these two new origins to others already documented, the researchers conclude that meat eating has evolved at least six times.
“The strength [of this study] is the comparative analysis,” says Maria Logacheva, a plant scientist at the Skolkovo Institute of Science and Technology, who was not involved with the work. “It nicely shows how the novel traits emerge.”
However, Victor Albert, a plant evolutionary biologist at the University at Buffalo, says Hedrich’s team does not have enough data to support the two new origins, especially because some genes essential to predation existed in an earlier ancestor common to pitcher plants and the three newly sequenced plants. His team is sequencing two additional sundew species to help clarify what happened.
But Luis Herrera-Estrella, a plant genomicist at Texas Tech University, is pleased to know about the new genes that are now linked to carnivory. He and others can study how genes were rewired to make meat eating possible. Indeed, Hedrich says, it seems most plants already have many of the necessary genes. “The path to carnivory seems to be open for all plants.”
sciencemag.org, 14 May 2020