Developing Rosetta Stones for Social Chemistry
by Andrew Palmer
One of the fundamental requirements for living systems is the ability to perceive and respond to signals in their environment. The exchange of signals between biotic (living) sources can result in complex social networks between organisms of both the same and different species. Some obvious examples are the use of colored pigments to attract pollinators to flowers or the importance of verbal communication in mammals and birds. While auditory and visual cues are critical to many organisms, the bulk of interorganismal signaling occurs through the exchange of small molecules. At the emerging interface between chemistry and biology the potential exists for the development of new tools and strategies for translating these molecular dialogues. The importance of deciphering such ‘social chemistries’ cannot be overstated with implications on human health, ecology, developmental and evolutionary biology, and more. Plants are the undisputed masters of such processes exchanging signals not only with other plants, but with a variety of other organisms including bacteria and insects. As a result plants are an ideal system for learning the basic rules of small molecule based interorganismal signaling.
Figure 1: Picture of the Parasitic Plant Striga Attached to Corn (left) and the Effects of Striga on Corn in the Carolinas (right)
One of the more interesting examples of plant-plant signaling is that of the parasitic plants in which one plant attaches to, and subsequently siphons resources from another. In these systems host derived signals can regulate multiple developmental stages of the parasite’s life cycle including germination, host attachment, and/or development of the aerial portions of the plant. Such interactions are not merely of academic interest but have substantial impacts on the health and well-being of subsistence farming communities. Throughout Africa and Asia, members of the Striga and Orobanche families parasitize crops such as corn, sorghum, millet, cowpea (black eye pea), sugar cane and potatoes with an estimated economic impact of over $7 billion annually. New protocols and/or GMOs which successfully reduce their impact could reverse a vicious economic downward cycle, allowing local communities to feed themselves, access education, and bring significant benefits to the health and sustainability of these rural communities.
Attachment to the host occurs through the development of a specialized organ unique to the parasitic plants known as the haustorium, the development of which in Striga, and many other parasitic plants, is initiated by specific host derived signals.
Figure 2: Development of Striga's specialized attachment organ (haustorium) in response to increasing concentrations of host derived chemical signals (From top left to bottom right).
My research has focused on evaluating the generation and perception of these signals employing a variety of techniques from fluorescence microscopy to organic synthesis. These studies have aided in the discovery of a novel proactive signaling process in which the parasite employs a ‘chemical radar’ for the purposes of host detection. Further analysis now suggests this mechanism is actually employed by a number of non-parasitic plants for the purposes of detecting the roots of competitor plants. Not only does this work report on a novel and potentially broadly occurring signaling process but it provides insight into the molecular origins of parasitism and new strategies for dealing with parasitic infestations.
Figure 3: Striga's "Chemical Radar" known as Semagenesis - An Active and Regulated Process of Signal Generation and Perception
Drew Palmer's Publications
- Palmer A.G., Chen MC, Kinger NP, and Lynn DG (2009) Parasitic angiosperms, semagenesis and general strategies for plant-plant signaling in the rhizosphere . Pest Manag Sci
- Keyes WJ, Palmer AG, Erbil WK, Taylor JV, Apkarian RP, Weeks ER, Lynn DG (2007). "Semagenesis and the parasitic angiosperm Striga asiatica." Plant J.
- Palmer, A.G.; Gao, R., et al. (2004). "." Ann. Rev. Phytopathology, 42: 439-64