Ion channels enable plants to outsmart some animals

Have you seen the video of the Venus flytrap eating flies? It’s amazing! See here, for example.

This plant has some very serious skills. Its leaves, which resemble an open clamshell, form a snap trap for small insects such as flies. Unsuspecting flies, lured by the irresistible scent of the plant, land on the trap hoping to taste some sweet nectar. But little do they know, they’re about to become the meal of the day themselves. The welcoming trap snaps shut in just a fraction of a second, leaving the fly with no chance of escape. And it remains shut until the fly is completely digested.

But how does the plant (which, by the way, Charles Darwin called “one of the most wonderful in the world”) know when a fly has landed on it? Well, not surprisingly, ion channels play a leading role here.

The inner surface of the trap is equipped with several touch-responsive trigger hairs. When a fly lands on the plant, it touches and bends those trigger hairs, which then translate the mechanical stimuli into action potentials that spread along the entire trap surface and initiate trap closure.

In 2021, the groups led by Joanne Chory and Ardem Patapoutian identified a mechanosensitive ion channel, dubbed Flycatcher1, that is thought to be one of the primary touch sensors in Venus flytrap. Flycatcher1 is a chloride-permeable, stretch-activated ion channel that selectively localizes to mechanosensory cells in trigger hairs, where it is expressed 85-fold higher than in trap tissue. The authors proposed that following mechanical stimulation, Flycatcher1 could contribute to membrane depolarization, leading to the generation of action potentials and subsequent closure of the trap.

Interestingly, if the fly touches the trigger hairs just once, nothing happens. For the trap to close, the fly needs to touch the trigger hairs at least twice within a short period of time (about 20 seconds). So, the plant somehow memorizes the first stimulus and then starts the countdown, waiting for the second stimulus to trigger the trap closure. The mechanism behind this is believed to be dependent on cytosolic calcium in the leaf trap cells. The first touch of a trigger hair causes a subthreshold rise in cytosolic calcium. A second touch will add up to the initial one, thus surpassing the threshold needed to trigger fast trap closure.

But the plant doesn’t stop counting after the trap is closed. It continues to add up subsequent touches to determine how many hydrolases and transporters it will need to synthesize in order to process the prey and absorb nutrients. So, the number of action potentials and calcium waves informs the plant about the size and nutrient content of the struggling prey. The more energy the prey has, the more it will try to escape the trap, and therefore stimulate more trigger hairs, leading to more action potentials, elevated calcium signals, and increased secretion of digestive enzymes.

So, the plant apparently uses a calcium clock to “count” the number of times the fly has touched the mechanosensitive trigger hairs.

How cool is that! Ion channels enable plants to outsmart some animals.