Labelled by Charles Darwin as a “most wonderful” plant, the Venus flytrap is more than a carnivorous curiosity. The rapid closing of its leaves when brushed by prey offers researchers a way to investigate how plants sense their environment through touch.
A recent study published in eLife unravels part of this mechanism. The research identifies a protein that seems to play a key role in touch sensitivity for flytraps and other meat-eating plants. The work could help plant scientists understand how other plants respond to mechanical stimulation, albeit via slower responses than the prey-ensnaring snap of the flytrap—such as how a root senses and grows around a rock.
“Flytraps are a fun system … I think they make great ambassadors for plant biology because people are interested in them,” says Carl Procko, a plant scientist at the Salk Institute for Biological Studies in La Jolla, California, who worked on the new paper. “But they are also pretty amazing examples of evolution.”
The researchers focused their attention on the microscopic and exquisitely sensitive trigger hairs that line the flytrap leaves. After growing genetically identical plants, they analyzed the different genes expressed inside thousands of hair cells. They knew what they were looking for: Previous studies have highlighted the likely role of ion channels, which pump molecules in and out of cells to produce electrical signals.
One candidate gene was expressed 85-fold higher in trigger hairs than other flytrap tissue. When the researchers added this gene, coding for a protein they call FLYCATCHER1 (FLYC1), to mammalian cells, they found the cells produced an electrical current when stretched by negative pressure applied through a pipette. The team also found the same protein in the touch-sensitive tentacles of the sundew, another type of carnivorous plant.
The FLYC1 protein is very closely related to a similar touch-sensitive molecule found in bacteria, Procko says, where it monitors osmotic pressure (osmolarity) and pumps ions in and out when the protein senses pressure on the cell membrane. “These channels in plants are probably osmolarity sensors,” he says. “It seems that through evolution they have taken these osmolarity sensors and put them towards touch.”
The study does not prove this protein is involved in the flytrap’s touch response. That would require a gene knockout study that grows genetically modified plants missing the protein, then investigates how they behave differently.
The researchers are working on such a knockout project. But modifying the genes of flytraps is a notoriously unreliable and difficult procedure, says Ueli Grossniklaus, a plant geneticist at the University of Zurich, Switzerland. “Transforming a plant is always tricky, you know, until you have the methods worked out. Even for many crops, we have no efficient transformation systems,” he says. “Very often this is done at companies because it’s a huge effort.” With no commercial interest in breeding carnivorous plants, only one academic group has successfully grown a genetically modified flytrap so far, he adds.
Rainer Hedrich, a plant physiologist at the University of Wuerzburg, Germany, who worked on that transgenic flytrap project and whose lab published the plant’s genome last year, says the ion channel identified in this paper is only part of the story. The FLYC1 protein transports negative chloride ions out of the plant cells. But that’s not enough to complete the process and generate the electrical signal. “You also need a calcium channel to conduct calcium inwards,” Hedrich says.
Previous studies suggest the flytrap sensitivity is driven by calcium transport—rather than chloride—because calcium spikes require two touches on the trigger hair in a short period of time. This helps the plant avoid closing its leaves when a falling twig or other inedible objects brush against them. “I think the calcium-permeable channel is the dominant one,” Hedrich adds. The eLife study does identify a likely candidate protein that would help generate the electrical signal—related to a calcium ion channel found in the Arabidopsis plant—but the researchers have not yet characterized it.