The genome of the Australian pitcher plant, which has slippery leaves that lead insects into a deadly cavity, has just been sequenced and has helped solve a longstanding mystery: why some plants become predators.

The Australian pitcher plant (Cephallotus follicularis) and other carnivorous plants, described in the journal Nature Ecology and Evolution, appear to have independently evolved their carnivorous ways, but they all have certain traits in common. For example, they likely started with a craving for meat, which turns out not to be so different from a craving for fertilizer.

"What the carnivores [in this case, plants] are after is phosphorous and nitrogen: fertilizer," said Victor Albert, a biologist at the University of Buffalo. "The prey animals have this in abundance in the form of the proteins and nucleic acids that are released when the plant digests them."

Albert worked on the genome pitcher plant project with lead author Kenji Fukushima and their team.

"Many of the extant carnivorous plants and their ancestors have grown on nutrient-poor habitats, like acidic freshwater wetlands," helping to explain why they turned to eating meat, said Fukushima, who began the project when he was a graduate student. He's now a postdoctoral research fellow at the University of Colorado School of Medicine.

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For the study, the researchers not only investigated the Australian pitcher plant, they also analyzed digestive fluids in three independently evolved pitcher plants and a sticky carnivorous plant, Drosera. Pitcher plants have deep cavities full of digestive fluid, while sticky meat-eating plants have leaves that are covered with goo. Like flypaper, the sticky leaves can then also trap insects.

Some carnivorous plants have also evolved clamshell-like snap mechanisms and even the ability to suck in prey underwater via suction traps.

The investigation found that although the various carnivorous plant lineages had split from a common ancestor more than 100 million years ago, each had repurposed genes, and their related proteins associated with stress response, to digesting meat.

Fukushima explained that many disease-fighting proteins in plants have the ability to break down basic cellular and extra-cellular components, such as a pathogen's protein, RNA and a fibrous substance called chitin.

"These compounds largely overlap with an insect's body components, and that might be one of the reasons why carnivorous plants were able to recruit pathogen-killing enzymes to carnivory," Fukushima said.

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Albert added that the digestive functions were basically already in place; they were just recruited and specialized to handle other tasks.

You might then wonder if more plants, if sufficiently stressed out, could become carnivores too. Both Albert and Fukushima said that's possible, although evolving a life of meat eating is not the universal solution to surviving in a harsh environment.

Fukushima did say that carnivorous plants all tend to live in sunny, moist places. One could therefore keep an eye on such areas that are nutrient-poor, but the wait would probably be long before a plant evolved into a carnivore.

As Fukushima said, "I don't know how many million years it takes."

Top photo: Carnivorous Australian pitcher plant, Australian pitcher plant Cephallotus follicularis. Credit: Mitsuyasu Hasebe

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