The Venus Flytrap: From Prey to Predator

    The carnivorous Venus flytrap recognizes its prey by taste and its cells share similarities with the human intestine. By exploiting common plant defense strategies, the flytrap has completely turned the table; it seeks out and consumes prey rather than being the meal itself.


    We have recently published our transcriptomic work on the Dionaea hunting skills:

    “Venus flytrap carnivorous life style builds on herbivore defense strategies“, Felix Bemm, Dirk Becker, Christina Larisch, Ines Kreuzer, Maria Escalante-Perez, Waltraud X. Schulze, Markus Ankenbrand, Anna-Lena Keller Van der Weyer, Elzbieta Krol, Khaled A. Al-Rasheid, Axel Mithöfer, Andreas P. Weber, Jörg Schultz, Rainer Hedrich.

    Genome Research, DOI: 10.1101/gr.202200.115



    Plants can do maths

    The carnivorous Venus flytrap carefully plans its meals: It can count how often it is touched by an insect to calculate the digestive effort. This discovery has been made by plant scientists of the University of Würzburg.

    Usually, plants are eaten by animals and humans. With carnivorous plants, however, it's the other way round: They have specialised in animals as an extra source of nutrition to help them survive in moors or other nutrient-poor sites. Take the Venus flytrap (Dionaea muscipula) for example: It has a trapping structure formed by the terminal portion of leaves and is triggered by tiny hairs on their inner surface. These sensors allow the plant to discover, catch and digest flies and other fast animals.

    The trap's insides are covered by a turf of red glands. This flower-like appearance combined with fruity smells attracts many insects. Looking for nectar, the visitors inevitably touch the three sensor hairs located on each of the lobes. Based on the number of times the trigger hair is stimulated, the plant decides whether to snap the trap closed and start digestion. This means that the plant is capable of counting.

    The discovery was made by an international team of researchers around biophysicist Professor Rainer Hedrich from the University of Würzburg. Their work has been published in the renowned journal Current Biology.

    Trap closes on "two"

    If a trigger hair on the Venus flytrap is stimulated only slightly, it will signal the first prey contact by transmitting a bio-electrical signal. "One signal does not yet cause a reaction – it could be false alarm after all," says Hedrich. But a second stimulation already causes the trap to snap close in the blink of an eye.

    If the prey stayed calm now, there would be no other signal. In that case, the trap will open again after a half day. But since the trapped animals usually put up quite a fight, they trigger a virtual fireworks of signals sealing their fate for good.

    This is because the Venus flytrap can count further, as Hedrich's colleague Sönke Scherzer found out. He measured that a trapped insect triggers some 60 signals per hour. To imitate the contact stimuli, Scherzer nudged individual sensory hairs up to 60 times in an hour to see what happened.

    Digestive juices start to flow from "five"

    The result: Two or more stimuli activate the pathway of the contact and wound hormone jasmonate JA. At five and more signals, the plant additionally activates the genes for digestions enzymes in all of its 37,000 glands. This activation does not take place if the jasmonate signal pathway is suppressed in experiments prior to mechanical stimulation. "We have thus proved that the electrical signal is converted into a hormone signal in the glands," Hedrich further.

    Five or more signals also stimulate the transport molecules that provide for the absorption of the digested insects into the plant. While searching for this mechanism, one gene caught the attention of Würzburg Ph.D. student Jennifer Böhm. It is activated by both touching the sensory hairs and by the hormone jasmonate. She was able to demonstrate that it is an ion channel which transports sodium. Large quantities of this nutrient salt accrue when the insects are digested.

    The plant can also do maths

    "We asked ourselves whether the trap can calculate how many channels it must provide to remove the sodium," Hedrich explains. Obviously, the plant is able to do that: The bigger the prey animal, the more fiercely it will struggle and the more frequently the sensory hairs are stimulated. In that case, the Venus flytrap will produce more ion channels than for a weakly struggling animal.

    And what about the plant's memory? According to Hedrich, the Venus flytrap can remember the number of prey contacts for at least four hours. Now the researchers want to study the molecular bases of retentivity and learn whether the sensory performance of plants and animals share similar underlying principles.

    Funded by the European Research Council

    Hedrich's exploration of the Venus flytrap and other carnivorous plants is backed by top-level funding: In 2010, the European Research Council (ERC) allocated him an "Advanced Grant" worth 2.5 million euros for this purpose. Within the scope of the ERC project "Carnivorom", Hedrich's team is on the lookout for those genes that make plants carnivorous.

    „The Venus flytrap Dionaea muscipula counts prey-induced action potentials to induce sodium uptake“, Böhm, J., Scherzer, S., Krol, E., Kreuzer, I., von Meyer, K., Lorey, C., Mueller, T.D., Shabala, L., Monte, I., Solano, R., Al-Rasheid, K.A.S., Rennenberg, H., Shabala, S., Neher, E., Hedrich, R., Current Biology, January 21, 2015, DOI 10.1016/j.cub.2015.11.057


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    How Plants become Carnivores

    What genes enable plants to catch animals and digest them? Three genes have now been described for the Venus flytrap. They are responsible for the fact that the plant can use the vital potassium from its prey highly efficiently.Carnivorous plants such as the Venus flytrap (Dionaea muscipula) grow in environments with extremely low nutrition. In order to survive there, they have specialized in the course of evolution: They obtain additional nutrition in the form of animals.The Venus flytrap catches its prey with leaves that have been reshaped into traps. When insects touch particular sensory hairs on the trap, it closes very quickly and turns into a kind of green stomach: Glands emit a hydrochloric acid mix made up of digestive enzymes and apart from nutrients, minerals such as calcium, magnesium and potassium are also released from the prey. The plant then imbibes this additional meal through its glands.


    PNAS publication of an international team

    It is particularly potassium that is crucial for plants. Carnivorous plants need it urgently for the operation of its traps. An international research team has now found out just how efficiently the Venus flytrap obtains the potassium from its prey. The results have been published in the renowned PNAS journal.

    Involved in the publication are the groups of the Würzburg biophysicist professor Rainer Hedrich and of the Göttingen neuroscientist and Nobel Prize winner professor Erwin Neher. They have collaborated with the professors Sergey Shabala (Australia), Heinz Rennenberg (Freiburg) and Khaled Al-Rasheid (Saudi Arabia).

    Concentrated action of two potassium transporters

    First findings: The glands in the flytrap can only absorb potassium when an insect was really previously caught. Next, the scientists analysed the genes that were activated for absorbing the potassium. The result was that two potassium transporters and one enzyme, a protein kinase are increased. It is exactly those three that are also connected with “normal”, i.e. non-carnivorous plants in the absorption of potassium in the root.

    This is what the interaction of the tree players looks like: The enzyme activates the two potassium transporters that take the entire potassium from the prey into the plant in one concentrated action. First of all the DmAKT1 transporter lowers the potassium level in the stomach of the Venus flytrap drastically, then the DmHAK5 transporter does the detailed work. “It has considerable pumping power and can still transport potassium into the gland cells when the potassium concentration there is already very high”, explains Sönke Scherzer, Hedrichs’ assistant.

    On the quest for the potassium sensor

    What the researchers want to find out next: How do the potassium absorption systems of the Venus flytrap notice that a potassium-rich prey, is sitting in the trap? Hedrich: “We have first indications that it is not the potassium that is initially released from the prey but rather contact to the sensory hairs that initiates the new synthesis of the transporters”.

    The following still has to be checked: How is the potassium concentration measured in the green stomach? How does the protein kinase receive the signal that it has to switch on both transporters? This potassium sensor that still has to be identified, would also have to switch the potassium absorption system off again when there is no more potassium in the stomach, guesses Hedrich: Then the trap opens again and is ready for the next catch.



    Funding by the European Research Council

    Hedrich drives the research of the Venus flytrap and other carnivorous plants forward with high-level funding: The European Research Council (ERC) has granted the Würzburg plant scientist an “Advanced Grant” of over 2.5 million euros in 2010 for this purpose. In the “Carnivorom” ERC project, Hedrichs’ Team is in search of genes that makes plants into carnivores.



    Calcium sensor kinase activates potassium uptake systems in gland cells of Venus flytraps, Sönke Scherzer, Jennifer Böhm, Elzbieta Krol, Lana Shabala, Ines Kreuzer, Christina Larisch, Felix Bemm, Khaled A.S. Al-Rasheid, Sergey Shabala, Heinz Rennenberg, Erwin Neher, Rainer Hedrich. PNAS Early Edition, 21 May 2015, DOI: 10.1073/pnas.1507810112


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