The real hustle: how a plant conned fungi

Plants are great producers – they’re the source of food for many of earth’s animals, insects and microbes. As autotrophic, primary producers, plants are rooted to the base of the food chain as firmly as they’re rooted to the ground. A famous food chain we learned in schools taught us that plant produces its own food using sunlight, carbon dioxide and water. A rabbit feeds on the plant. A fox eats the rabbit. And when the fox dies, microbes eat (decompose) the fox’s body, which then goes back to the ground. Microbes are therefore on the top of the food chain as they feed (infect) on animals and plants.

Plants are producers that sit at the bottom of the food chain.

Some plants have found ways around this rule. For example, the Venus flytrap, a carnivorous plant, preys on insects and ants by trapping them in its leaves. Some plants, like mistletoes, are parasitic and grow on another plant. Mistletoes penetrate the host plant through its modified root called haustorium to absorb nutrients.

Highly successful fungal parasites also use haustorium to infect and steal nutrients from plants. However, fungi aren’t always parasitic. Some fungi and plants form beneficial partnerships called mycorrhizal symbiosis, in which the fungus colonises the root of the host plant. In the plant-mycorrhizal mutualism, the fungi gains sugars fixed by plants and in return, the fungi provide the plant with vital nutrients from the soil.

Non-photosynthetic plants

Photosynthesis is a process that’s fundamental to the identity of plants. Despite finding alternative food sources, the plants above still perform the process photosynthesis. However, like fungi, Monotropa uniflora or the Indian pipe, is so rebellious that it doesn’t follow any of these rules. In fact, it’s so much off the radar; it acts as a parasite that leeches off fungi.

The India pipe is often mistaken for a fungus, while some call it the “ghost plant” due to its white appearance. This is because the Indian pipe lacks chlorophyll pigments, which gives plants their green colour. The Indian pipe is non-photosynthetic as it lacks genes required for photosynthesis.

 

Venus flytraps feed on insects by trapping them in their leaf structures but they can still carry out photosynthesis.

As the Indian pipe can’t photosynthesise, it doesn’t fit into the “producer” category of the food chain either. Remarkably, there are over 3,000 species of non-photosynthetic plants, which means they must find an alternative food source to survive. A few of them are members of the Ericaceae family, which includes the Indian pipe. The Ericaceae are a family of flowering plants (angiosperms) that contain important economic plants like blueberries, cranberries and Rhododendron.

Indian pipes can grow in dark, dense forest floor covered by leaves and debris. These perennial wildflowers are dispersed across the Northern hemisphere and typically grow 10-30 centimetres tall. Each stem of the plant bears a single, white flower. The stem arcs at the tip so the young, closed flower points towards the ground, which ensures that the pollens are protected from rainwater. Once the flower matures, it opens up and points slightly, but not completely, upwards. This still protects flower from rainwater and also makes the flowers more accessible to insect pollinators.

Monotropa uniflora, the Indian pipe or ghost plant, is often mistaken for a fungus due to its appearance.

The Indian pipe is apparently somewhat edible (I don’t recommend it though!) but it’s more useful for medicinal purposes. It contains constituents that act as a nervine, a sedative and a pain-reliever. Indian pipes have nervines to calm the nerves, so they’re useful to treat seizures. The clear fluid from stems was used by Native American Indians to treat eye problems. One of the main ingredients in the plant is salicylic acid, which can be used to treat warts. Despite the appeal of these plants, they’re tough to propagate so they remain perennial wildflowers.

Reversing the food chain

The Indian pipe is a myco-heterotroph, which means that it forms a parasitic relationship with fungi. The plant only feeds on one group of mycorrhizal fungi, the Russula mushrooms. These fungi form a beneficial partnership called mycorrhizal symbiosis with photosynthetic plants. The fungus provides soil nutrients to the plant, and in return, it receives fixed carbon that can be readily used as food.

Some fungi infect major crops causing severe economic damage and food loss but mycorrhizal fungi are beneficial for plants.

As non-producers, Indian pipes trick the fungus – already in a mycorrhizal symbiosis with another photosynthetic plant – to form a new mycorrhizal partnership. But as the Indian pipe can’t carry out photosynthesis it doesn’t provide the fungus with fixed sugar. In fact, the Indian pipe somehow steals the sugars from the fungi that it gets from its mycorrhizal symbiosis from a photosynthetic plant. Therefore, the sugars, which the Indian pipe uses for growth and survival, come from another plant via the mycorrhizal fungi. Even though these fungi are beneficial and not parasitic, it’s still remarkable for a plant to con and steals food from fungi for survival. The Indian pipe has flipped the food chain upside down.

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