Defensive Interactions Between the Parasitic Plant Cuscuta Pentagona and its Host
Plants must respond to stimuli to grow, reproduce, and protect against enemies. To defend themselves, plants produce chemicals that reduce the likelihood of attack. Furthermore, plants can communicate by releasing volatile chemicals into the air. Because they defend themselves and communicate chemically, plants have been postulated to communicate to one another when they come under attack by herbivores. This communication may serve to prime defense responses in undamaged plants near neighbors under attack. Cuscuta species are non-photosynthetic, parasitic plants that rely entirely on hosts for nutrients. Cuscuta vines locate hosts by following volatile chemicals of potential hosts, but literature relating to the specific compounds and mechanisms used by Cuscuta is scant. Upon contact, Cuscuta develop haustoria, specialized organs that penetrate the vascular tissue of the host through which the parasite absorbs nutrients and water. Individual Cuscuta attach to a multitude of plants, spreading a vast network of vines to intake nutrients. Molecules besides sugars and nutritionally relevant compounds can move bidirectionally between the host plant and Cuscuta via haustoria. This raises the possibility that Cuscuta transfers defense signaling hormones among hosts. Furthermore, the biosynthesis pathways of some plant defense molecules take place partially in chloroplasts, an organelle not found in Cuscuta. Therefore, I hypothesize that Cuscuta, use defense hormones synthesized in their hosts to develop their own defense. To test the hypothesis that Cuscuta can acquire defense molecules from its host plant, I plan to isolate, from both the host and Cuscuta, RNA relevant to defense pathway genes (specifically the salicylic acid or jasmonate pathways), as well as the molecules themselves. These should be induced after infestation by vascular feeding herbivores such as aphids. To determine the source of salicylic in Cuscuta, I would attempt to radiolabel salicylic acid in the host so that it can be distinguished from Cuscuta-based salicylic acid, if such genes are found to be active in Cuscuta. Alternatively, infesting only the Cuscuta while keeping the host free of herbivory, may allow for distinguishing Cuscuta-based salicylic acid from host-based salicylic acid. Subsequently, I would like to assess whether or not Cuscuta are utilizing host salicylic acid in their own defense pathways, or if the hormone is being transmitted to other plants via Cuscuta. Currently I am testing Cuscuta with five host species to see which host best supports parasitic infection.
Martin, Timothy, "Defensive Interactions Between the Parasitic Plant Cuscuta Pentagona and its Host" (2018). University Research Symposium. 93.