The carnivorous plants of Asia, Australia and the Americas share a common trait despite the distance that separates them: the genetic machinery for digesting insects. Carnivorous plants, which live in nutrient-poor habitats, capture insects by setting a trap from which they can hardly escape. Once trapped inside the leaves, the prey fall into digestive fluids that break down their flesh and exoskeletons to compensate for the plants’ nitrogen and phosphorus deficits. This is the method used by all carnivorous plants in Australia, Asia and America, despite having evolved independently.
A new study, published in Nature Ecology & Evolution, has delved into the origin of these plants and has identified the genetic changes that have allowed adaptation to a carnivorous diet in some plants. To do so, the team, led by the National Institute for Basic Biology of Japan and with the participation of the University of Barcelona (UB), examined three species: the Australian Cephalotus follicularis, the Asian Nepenthes alata and the American Sarracenia purpurea.
The experts sequenced the genome of the pitcher plant (Cephalotus follicularis), a species native to Australia that has well differentiated insectivorous leaves – pitcher-shaped traps for catching insects – from non-insectivorous leaves (like those of other plants).
The genome of this species – the second carnivorous plant with sequenced DNA after Utricularia gibba – is relatively large, consisting of 1.6 Gbp, which is almost half of the human genome. In total, the researchers identified more than 36,000 genes.
Genetic analyses show that, during their evolution towards a carnivorous diet, insect-trapping leaves have acquired new enzymatic functions. “This is a very specific set of proteins that have evolved to act as digestive enzymes,” says Pablo Librado, another of the authors who is currently working at the Center for Geogenetics at the University of Copenhagen.
Over time, in all three species, families of plant proteins that originally aided in self-defense against disease and other threats evolved into the digestive enzymes seen today, such as basic chitinase – capable of breaking down chitin, the main component of prey exoskeletons – and purple acid phosphatase – which allows plants to obtain phosphorus from decomposed bodies.
“This suggests that there are limited and restricted pathways that lead them to become carnivorous plants,” says Victor A. Albert, of the University at Buffalo (USA) and one of the authors of the paper. “These plants have a genetic toolkit, and they try to find an answer to become carnivorous, and in the end, they all arrive at the same solution,” he adds.