The UW-Milwaukee Field Station is hardly the Little Shop of Horrors, but it’s still the home of some fascinating carnivorous plants. Now, thanks in part to a UWM biologist, scientists have a better understanding of how those carnivorous plants digest their insect prey.
UWM Biological Sciences Professor Erica Young is part of an international team that studied the microbiome of the plant Drosera, commonly known as sundew. Together, these scientists identified a species of fungus, called Acrodontium, which is integral in helping sundews digest their prey. Their work was published in August in the journal Nature Microbiology and was shared as a “research highlight” in Nature Plants.
“(This discovery) tells us a little bit about how collaboration is successful,” Young said. “You have to collaborate with other types of organisms, and that also provides a way for diversity to be maintained and to thrive. That’s what life on Earth is about.”
Sundews need fungus to thrive
When people think of carnivorous plants, they’re likely to picture a Venus Flytrap. “I think we have Audrey II to blame for that,” Young laughed, referencing the man-eating plant from the 1986 musical “Little Shop of Horrors.”
But, said Young, carnivory as a survival method has cropped up in several different species, including Venus Flytraps, pitcher plants, and sundews, even though these species are not closely related. Each can photosynthesize, but they live in places where there is not much nutrition in the soil. They gain those nutrients instead by consuming ‘bugs’. Each have different methods for trapping their prey.
Sundew of the genus Drosera secrete a sticky, sugary substance on their surface hairs that attracts insects. Once an unlucky mosquito or gnat lands on the plant, it gets stuck and can’t fly away. Some sundews can also curl their hairs over the prey to prevent their escape. The plant produces enzymes that help break down insects, including the chitin in insect exoskeletons.
But scientists wondered how the plant actually digests insects. A group of researchers from Taiwan led the study by examining genetic information from sundews in Asia, where they found evidence of the role of a fungus called Acrodontium. Young examined the Drosera rotundifolia that grows at the UWM Field Station at the Cedarburg Bog in Saukville, Wisconsin, while other researchers tested plants in the United Kingdom.
“In Taiwan, in the UK, and here in Wisconsin, we found the same species of fungus with the sundews, and so we think that this is a very close relationship that they may have been developing for some time,” Young said. Other plants such as legumes have a tight association with bacteria that live in their root nodules. “We think that this fungus-sundew association … may be on their way down a path towards symbiosis, which means that both benefit from the collaboration.”
Think of how humans rely on a microbiome for digesting our food, Young added.
“If we didn’t have bacteria in our gut, we would not do very well in terms of digestion,” she said. “It’s similar – this particular fungus seems to be really important for helping the sundews break down their prey.”
The sundews look to be a nice home for the fungus. Acrodontium is acidophilic, meaning that it prefers acidic conditions in the secretions of a Drosera, so gaining a habitat and food from insect prey digestion.
Research into Pitcher Plants
Sundews are not the only carnivorous plant in Cedarburg Bog. With teams of graduate and undergraduate students, Young has spent much of her career at UWM studying pitcher plants. Their leaves form a hollow tube that can fill with rainwater, and the plant recruits a community of microbes and mosquito and other larvae.
“It’s a whole little ecosystem in there, and it’s served as a model for community ecology for a number of decades,” Young said.
But unlike sundews, she added, pitcher plants don’t produce their own digestive enzymes. So how do they get nutrients from the insects that happen to fall inside of the pitchers? Research across North America shows that pitcher plant microbial communities are critical to prey breakdown. Young and collaborators across the United States are investigating with the help of a National Science Foundation grant that was awarded in 2020.
“When these pitchers (first) open, they’re sterile, as far as we understand,” Young said. “What is the process of new bacteria coming in? How does the microbial community change over time?”
Using genomic approaches, Young and her colleagues are studying pitcher plants from the Florida panhandle to the northern reaches of Quebec, and even plants in Switzerland. They’ll compare and contrast the plants’ microbiomes to gain more insight into how these micro-ecosystems form and change. Young and her collaborators are analyzing data from transcontinental sampling in 2022, with several manuscripts in preparation.
These plants are less scary than Audrey II – but they will provide new insights into how flora, fauna, and their microbiomes depend on each other.
By Sarah Vickery, College of Letters & Science