Parasitic plants form signaling networks between plants, transmitting warning signals when insects attack.
A team of scientists from the Kunming Institute of Botany in China and the Max Planck Institute for Chemical Ecology in Jena, Germany, has discovered that the parasitic plant Cuscuta (dodder) not only depletes nutrients from its host plants but also serves as a key “intermediary” in the signaling network between neighboring plants when insects attack.
Dodder, a parasitic vine, grows quickly and invades its host plants by inserting haustoria (a specialized organ similar to roots) into the host’s stems, absorbing water and nutrients. Dodder vines often connect different host plants, forming a network. If any plant in this network is attacked by herbivores, neighboring plants that are unaffected activate their defense genes, putting them on alert and increasing their resistance to the pests.
The Cuscuta genus consists of leaf- and rootless parasites that grow on their host plants without touching the soil. By fusing their vascular systems with those of the host plants, dodder forms a complex network to extract nutrients.
The research team, led by Dr. Jianqiang Wu from the Kunming Institute of Botany and Professor Ian Baldwin from the Max Planck Institute for Chemical Ecology, has investigated the ecological significance of dodder. They sought to determine whether dodder not only steals resources from plants but also plays a role in transmitting information between them. “We know plants can communicate through volatile signals and underground mycorrhizal networks, so we wanted to see if dodder could transmit insect feeding-induced signals and activate defenses,” explains Dr. Wu.
Dodder Parasitism and Signal Transmission Among Host Plants
Dodder causes significant economic damage in agriculture, particularly in pasture farming and soybean production. To study this, the researchers used soybean plants but also connected thale cress, tobacco, and wild tomato to dodder networks. To trigger defensive responses, caterpillars of Spodoptera litura, an agricultural pest, were placed on the plants.
By analyzing the transcriptomes—active gene expressions in the leaves of plants connected to dodder—the scientists found that plants attacked by insects could transmit defense signals through the dodder bridges to neighboring plants. Using RNA sequencing, they found major changes in the gene expressions of both attacked and unaffected leaves of the same plant, and, crucially, in the neighboring plants.
The study found that the plant hormone jasmonic acid played an important role in dodder-mediated systemic signaling. After insect feeding, defense signals were rapidly transmitted between plants through the dodder network, even across long distances. Alarm signals were exchanged between different plant species as well.
Future Research Directions
The team plans to further study the mechanisms of signal transfer through parasitic bridges. In the current study, they used a chewing caterpillar, Spodoptera litura, to induce defense responses in plants connected by dodder networks. The researchers now want to explore whether piercing-sucking insects, like aphids, trigger a different set of defense signals and how these are transferred by dodder. They also aim to identify the specific substances responsible for signal transmission.
Professor Ian Baldwin concludes, “Ecological interactions in nature are extremely complex. A parasite steals valuable nutrients from its host, but at the same time acts as an important intermediary to warn neighboring plants. Whether this warning is truly altruistic remains to be further studied.”
