Plants with an appetite for meat: how did the carnivores develop their bizarre insect-catching skills? The genomes of venus fly trap, sundew and water trap now provide surprising information. Interesting processes of genetic adaptation therefore formed the basis for the development of their rabid diet.
Many animals eat plants – but around 600 plant species have turned the tables: they use clever trap systems to hunt for insects. This gives them growth advantages in locations where the soil offers little nutrients. These so-called carnivores have developed different strategies to catch flies, ants and the like: some set up pitfalls, others stick and some snatch for their prey. After a successful hunt, digestive fluids break down the victims so that the plants can absorb the nutrients.
The rabid plants have long been the focus of research. Among other things, their evolutionary history raises questions: How did they emerge from peaceful ancestors and on which genetic programs are their bizarre abilities based? It already seems clear that the carnivore has developed several times independently of one another with different groups of plants. An international team of researchers headed by Rainer Hedrich from the University of Würzburg has now dedicated a genetic test to three representatives of the dew family (Droseraceae). As part of their study, they sequenced and analyzed the genome of the Venus flytrap (Dionaea muscipula), the water trap (Aldrovanda vesiculosa) and the sun dew species Drosera spatulata.
Targeting three green carnivores
The interesting thing about the trio is that although these plants belong to the same family of plants, they have conquered different habitats and developed different catch mechanisms: Dionaea lays traps that, like traps, trap insects in a flash after they have touched fine sensory hairs. Aldrovanda, on the other hand, is an aquatic plant that lurks fleas with bubble-shaped catch organs: at the slightest touch, a flap opens, causing water to flow into the traps and dragging the victims with them. The sundew, in turn, relies on adhesive power: it catches its prey with sticky tentacles that increasingly enclose the insect after the success of the hunt and ultimately decompose it.
After the researchers had sequenced the genome of the three carnivores, they compared the sequences with one another and with the known genome data of other plants. This showed that despite their different ways of life and catching mechanisms, the venus fly trap, sundew and water trap share a common “basic equipment” of hereditary systems that form the basis of their carnivorous way of life. “The function of these genes is related to the ability to sense, digest and utilize their prey,” concludes Hedrich.
One might think that the carnivorous abilities are based on a particularly extensive genome. But apparently the opposite is the case: To their surprise, the researchers found that the three species examined were among the poorest plants known. Drosera has 18,111, Dionaea 21,135 and Aldrovanda 25,123 genes. Most plants, on the other hand, have between 30,000 and 40,000 genes. “This can only mean that the specialization in animal food was accompanied by a gain, but at the same time a massive loss of genes,” says co-author Mitsujasu Hasebe from the Japanese University Okazaki.
Active root genes in the traps
As the previous analysis results show, most of the genes that are necessary for the operation of the capture organs can be found in a slightly modified form in “normal” plants. “In the case of the carnivores, several genes are active in the trap systems, which develop their effects in the roots of other plants. These genes are only switched on in the traps when the prey is safely caught, ”explains Hedrich. As the researchers explain, it fits with this finding that venus flytrap and sundew only develop weak root systems. They are even completely absent from the waterfall.
The researchers also found evidence of an interesting genetic effect that apparently favored the development of the new abilities: about 60 million years ago, the common genome of a doubled ancestor of the three plants had doubled. This duplication made copies of genes available for further development, the scientists explain. “We were able to trace the origin of the common carnivory genes back to this duplication event,” says co-author Jörg Schultz from the University of Würzburg.
The researchers now want to use the three genetic blueprints as the basis for further studies. Among other things, they should now help to find out more about the molecular basis of the capture mechanisms. One aspect seems particularly exciting: “We found that the Venus flytrap counts the electrical stimuli triggered by the prey, can remember this number for a certain time and finally makes a decision that corresponds to the number,” says Hedrich. The scientist says that the biophysical-biochemical principles underlying this astonishing ability could also shed light on genetic information.
Source: University of Würzburg, technical article: Current Biology, doi: 10.1016 / j.cub.2020.04.051