Venus flytrap digestive proteome

August 14, 2012 § Leave a comment

Like me, you’ve probably watch in fascinated horror as a Venus flytrap snaps its jaws around an unsuspecting fly. But have you paused to wonder what’s in its digestive juices? In a recent Molecular & Proteomics paper, researchers report the analysis of all the proteins in the digestive juice of the carnivorous plant, and they found that the molecules are very different from the ones in animal digestive juices.

The Venus flytrap (Dionaea muscipula) hails from the Carolinas. It grows especially well around the North Carolina port city Wilmington, according to the North Carolina History Project.

The Venus flytrap has fascinated people for centuries, including Charles Darwin, who in his book “Insectivorous Plants” described it as “one of the most wonderful plants in the world.”  The plant eats flies and spiders (not bees and wasps, which probably move too fast for it) mainly for their nitrogen content. The nutrients give the plant a competitive edge to grow in the swampy lands of the Carolina coast.

(Creepy fact: Death comes slowly to the trapped animals. Scientists have shown that ants trapped inside the plant’s lobes are still alive eight hours later.)

Scientists have established that the plant can lure, actively trap, kill and digest insects. It’s even able to tell apart prey and objects accidentally caught in its jaws. But “very little was known about the enzymes used by Venus flytrap during the digestion of its prey,” says Jan Johannes Enghild at Aarhus University in Denmark, adding that the identification of the enzymes used by the plant likely would provide some insight into its digestive mechanism.

Enghild and colleagues wanted to find out what were the proteins in the digestive juice of the Venus flytrap. They didn’t want to contaminate the plant’s digestive juice with proteins from an insect victim, so they first had to devise a way to trick the plant into thinking it had prey within its jawlike lobes and to start secreting its digestive juice.

The investigators’ approach was to tickle the trigger hairs inside the trap lobes with small magnets or strips of paper. The plant clamped its lobes around the object and began to secrete its digestive juice.

The investigators then did deep sequencing of cDNA to find all the transcripts, followed by mass spectrometry to identify all the proteins in the juice. They found peroxidases, phospholipases, chitinases, proteolytic enzymes and a host of other proteins.

The Venus flytrap digestive fluid, much like ours, has a low pH. But that’s where the similarity ends.  In vertebrates and other carnivorous plants, such as Nepenthes, the proteolytic enzymes are mostly aspartic proteases. Enghild’s team found that cysteine proteases were the most  abundant class of proteases in the Venus flytrap, followed by a serine carboxypeptidase and aspartic proteases. The chitinases are probably present to degrade the exoskeleton of  trapped insects.

As Enghild notes, most of the abundant proteins were ones related to pathogenesis, which suggests the Venus flytrap’s digestive system evolved from defense-related processes. Enghild says his group is now making recombinant versions of the major proteins to better understand their biochemical properties.

Despite its adulation by scientists since Darwin, the Venus flytrap’s numbers in the wild are in trouble. (As you can tell from the YouTube video, you can get them as house plants). Only an estimated 35,000 plants are left in their natural environment. The flytrap became officially protected by North Carolina in 1956 and is still listed as a species of special concern by the Conservation of Nature and Natural Resources.

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