Establishing which genes’ mutations have enabled plants to devour prey
For all the multitudes of plants that depend on insects for help with pollination, there are well over 500 species that would rather just eat the bugs instead. Digesting animal flesh isn’t the expected behavior for a plant, but it’s sort of a popular idea, having evolved independently over and over again. Scientists have long known that these species arrived their common diet via convergent evolution, but only recently have they looked at the exact genetic pathways that enabled each one to consume insects.
Scientists started by probing the genes responsible for the all-important digestive enzymes that make these plants possible. Across various species, genes that would trigger the production of starches and sugars in normal leaves (which carnivorous plants have as well) were modified to make enzymes in the digestive organs of the plants, such as the pitch of an Australian pitcher plant (Cephalotus follicularis). Additionally, many proteins that were once tailored to fend off fungi by breaking down the chitin in their cell walls were also repurposed for digestion, instead being aimed at the chitin in insect exoskeletons.
No single way to secure a meal
While the digestive juices of carnivorous plants were remarkably homogeneous, the adaptions each species employs to capture insects were not. The disparate origins of these flora was much more apparent when looking at how they immobilized their prey before eating it, ranging from the aforementioned pitchers to tiny suction cups spread out over the leaves of bladderworts. Sundews have thin, sticky needles spread across tentacle-like structures. So-called lobster-pot traps like corkscrew plants essentially funnel their prey towards their digestive organs in a more mechanical, one-way trip. And of course, Venus flytraps have a mechanism to “snap” shut, clamping down on prey with specialized leaves.
Each of these chemical and mechanical specializations are more closely connected to the specific lineages these plants evolved from. It seems that while there are many ways to capture food, given enough time there is really only one way to digest it, particularly since in the end each species is trying to fill very similar nutritional needs.
Source: How Plants Evolved into Carnivores by Ewen Callway, Scientific American