EU researchers discover how the Venus flytrap became a predatory plant
The EU-funded CARNIVOROM project has published research detailing how the Venus flytrap’s genome has allowed it to become an insect-feeding carnivorous plant.
Venus flytraps have fascinated biologists for centuries due to the fact that the molecular underpinnings of its carnivorous evolution have remained largely unknown. Publishing in the journal Genome Research, researchers from the CARNIVOROM project have now cast light on this enduring biological mystery.
The Venus flytrap is by no means the only carnivorous plant – the sundew plant snares prey with sticky tentacles and pitcher plants use beckoning pools of enzymes to attract their next meal. The aggressive feeding habits of carnivorous plants allow them to survive in poor soil by giving them a new source of nitrogen and other nutrients. Many biologists have long suspected that this predatory behaviour evolved when the ancestors of today’s carnivorous plants turned typical defence mechanisms against insect pests into offensive weapons.
This hypothesis has now gained further support following a detailed genetic study of Venus flytraps undertaken by the CARNIVOROM team, led by biophysicist Professor Rainer Hedrich and bioinformatician Professor Jorg Schultz of the Julius Maximilian University in Wurzburg, Germany.
Specifically, Venus flytraps recognise their prey by using touch-sensitive trigger hairs located on the trap’s inner surface. When simulated, these hairs generate an electric signal that is transmitted to the plant. After the first stimulus, the trap remembers the signal but does not close; it is only after the second stimulus that the trap snaps shut. Prey that is captured will repeatedly activate the trigger hairs leading to repetitive electrical signals that are ‘remembered’ by the plant.
To date, no carnivory-specific genes have been indentified in Venus flytraps. To understand the molecular pathways involved in insect feeding, the researchers from Germany and their partners in Saudi Arabia generated genome-wide transcription profiles of traps before feeding and then again after they had snared a cricket and began to digest it alive. They then compared these genome profiles to other plant tissues.
Non-stimulated traps have gene expression patterns that largely resemble a leaf base, supporting the common assumption that traps are modified leaves. However, the glands inside the trap, which promote insect digestion and are activated after a few hours to help it absorb nutrients from its meals, more closely resemble the genetic expression pattern of roots. These are of course essential for nutrient acquisition for non-carnivorous plants.
The key to the Venus flytrap’s extraordinary evolution appears to revolve around chitinase, an enzyme that digests chitin in insect exoskeletons. ‘Contact with chitin normally means danger for a plant – that insects will eat the plant,’ Prof. Hedrich commented. ‘In the Venus flytrap, these defensive processes have been reprogrammed during evolution. The plant now uses them to eat insects.’
The researchers also used electron microscopy to study the ultrastructure of the trap’s glands, finding specialised cell layers involved in active secretion, nutrient transport, lipid energy stores, and protein biosynthesis necessary for trap function.
Funded partly by the European Research Council (ERC), the CARNIVORUM project officially ended in February 2016 and received nearly EUR 2.5 million in EU funding.