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Venus Flytrap's Insect Eating Connected to Plant Defense Genes

NEW YORK (GenomeWeb) – As a Venus flytrap snaps shut on unsuspecting insect prey, activation of its trap marshals the expression of genes coding for digestive enzymes, nutrient transporters, and proteins that other plants use to defend against insects, according to a study published today in Genome Research.

Researchers from Germany and Saudi Arabia teamed up to track transcriptional patterns, protein secretion profiles, and structural details in samples from Venus flytrap, Dionaea muscipula, before and after trap stimulation. Their results highlighted similarities between genes that are enhanced during Venus flytrap feeding and those expressed in Arabidopsis plants experiencing stress or predation by insects.

"In the Venus flytrap, these defensive processes have been reprogrammed during evolution. The plant now uses them to eat insects," University of Würzburg researcher and corresponding author Rainer Hedrich said in a statement.

The hairs on the surface of the Venus flytrap's trap respond to the slightest touch, sending electrical signals to the rest of the plant when nudged. But the trap does not close until the Venus flytrap receives a second signal, the team explained, confirming the prey's presence. After the trap is closed, meanwhile, the plant adjusts its response based on the size of the prey and the number of trap hairs it touches.

As part of Carnivorom — a European Union-funded effort to untangle the molecular roots of carnivory in the plant kingdom — the researchers took a closer look at the molecular features that facilitate this process, using Illumina HiSeq RNA sequencing to assess gene expression in various flytrap tissues.

Along with the transcriptome profiling, the researchers used proteomic analyses of flytrap digestive fluid to verify patterns of secreted protein that were predicted by the expression data. In parallel, they performed a detailed examination of the Venus flytrap's trap glands with electron microscopy to tease apart which tissues contribute to its secretory, transport, and energy storage capabilities.

In the trap gland tissue itself, for example, the team detected gene expression patterns that were similar to those found in the roots of non-carnivorous plants, though other Venus flytrap structures had more leaf-like gene expression characteristics.

In tissue from traps stimulated with insect prey, the researchers saw a jump in the expression of transport, signal transduction, and stress response genes. By folding in proteomic data, they uncovered a notable rise in the trap's secretion of hydrolase enzymes, which are expressed in the hour or two after a Venus flytrap catches its prey. Subsequent stimulation appeared to maintain expression of chitinase enzymes that degrade insects' tough outer covering for up to a few days.

Overall, the investigators noted that the trap-expressed compounds that tended to line up quite well with those that non-carnivorous plants use to sense and defend against insects and to heal herbivore-induced wounds.

"In this study, a comparative analysis of the transcriptomic profiles of non-stimulated versus active traps and gland demonstrates for the first time that, as well as hydrolases, a plethora of stress-associated pathways, including [reactive oxygen species] and [programmed cell death] signaling, are predominant in the activated Dionaea plant," they wrote.

With the Venus flytrap in the bag, the researchers are now getting set to look at related plants with so-called 'proto-carnivorous' lifestyles, including a plant called Plumbago, as well as plants with a history of carnivory and/or carnivorous and non-carnivorous life stages, Hedrich said. "Ultimately, we want to know what equipment a plants needs to eat and live off animals."