Quirks & Quarks

Recycling spare genes was how some plants turned into carnivores

'They were able to move genes for nutrient uptake from the root to the leaf to make the leaf a root'

'They were able to move genes for nutrient uptake from the root to the leaf to make the leaf a root'

Carnivorous plants, like this Venus flytrap, derive most of their nutrients by consuming animals, most commonly flying, foraging, or crawling insects and have adapted to grow in places where the soil does not contain enough nutrients for them to survive. (Adam Berry/Getty Images)
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Meat-eating plants like the Venus flytrap became the most successful green hunters on the planet by repurposing a duplicated set of their root genes. 

"They were able to move genes for nutrient uptake from the root to the leaf to make the leaf a root, which allows them to mine the prey," said Rainer Hedrich, a professor of biophysics and botany at the University of Würzburg in Germany.

Carnivorous plants are unique in the plant world for turning the tables in the food chain — so instead of animals eating plants, they eat the animals. 

Hedrich told Quirks & Quarks host Bob McDonald that he wanted to find the genetic roots of carnivory in plants. 

Plants normally use their roots to pull nutrients up from the soil, but carnivorous plants have adapted to absorb those same nutrients from their prey.

"In the places plants normally live, they have enough nutrients in the soil, but in some spots — in swamps for example, there is a depletion in nutrients and that means the plants starve," explained Hedrich. Carnivory was an adaptation that helped some plants survive in nutrient-poor soil. 

To figure out how these plants became hunters, he compared the genomes of three different, yet related carnivorous plants: the famous Venus flytrap, the waterwheel, which uses tiny traps to hunt aquatic crustaceans, and the sundew, which has sticky tentacles that roll up around trapped insects. 

These are the three carnivorous plants Hedrich and his colleagues studied: A: waterwheel (Aldrovanda vesiculosa), B: Venus flytrap (Dionaea muscipula) and C: sundew (Drosera spatulata). (Rainer Hedrich/Current Biology)

"They are all in the same family of plants, so this is very important if you want to go into the genomes and compare their software and hardware to drive a trap," he said. 

Genes to spare gave the plants a chance to tinker 

After sequencing and analyzing the genomes from these sister carnivorous plants, he discovered a "genome duplication event" that took place around 60 million years ago, when a common ancestor to these plants ended up with an extra set of genes in their genomes. 

Hedrich said this extra set of genes gave the plants a "playground to play with a new set of genes." These spare genes were the raw material for the plants to work on to generate genetic solutions to getting nutrients. 

They gave up [their] root function and now have all root functions only in their trap.- Rainer Hedrich, University of Wuerzburg

Random changes in these spare genes would sometimes produce an advantageous trait — like absorbing nutrients from insects. Plants with that trait would have a survival advantage over their neighbours.

"You maintain the old set of genes in your normal mother [and] father genome, and then that daughter genomes you can use to play around and see how you can modify some genes to favour new skills you want to gain, like carnivory," he said.

The right genes to become a skilful green hunter

Hedrich and his colleagues found the three carnivorous plants he studied, despite their differences, had a common basic set of genes essential for their hunting and insect-eating abilities.

"We found genes required to lure the insects," Hedrich said. These genes produce a "deadly odorant" that attracts insects.

They also found "the so-called touch genes" that convert the electrical signal produced when the insects move around on the traps into a hormone. That hormone then triggers genes that make enzymes allowing the plant to break down the insects and digest their juicy nutrients. 

Sundew (Drosera spatulata) carnivorous plants have a sticky substance on its leaves that acts like glue, holding an insect in place until the leaves curl up and trap it. (GUILLERMO LEGARIA/AFP via Getty Images)

Nutrient genes in roots rendered redundant

Once the plants were able to get the nutrients they needed from their leaves instead of their roots, maintaining that capacity in the roots was no longer necessary.

"We found, amazingly, that a whole lot of normally root-located genes got lost," said Hedrich.

Of the three plants he studied, the waterwheel no longer has any roots at all. The other two, the Venus flytrap and the sundew, only have minimal roots left over to pull up water and provide structural support so the plants don't fall over. 

"They gave up [their] root function and now have all root functions only in their trap."

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