Dioscorea sansibarensis is an African species of yam, and is the only monocot species known to be engaged in leaf nodule symbiosis. In this symbiosis, high densities of bacteria are packed within specialized glands formed by folding of the leaf acumen or drip-tip. Very little is known about this system, but preliminary data indicate that leaf acumens are colonized by a single, novel species of bacteria. Preliminary evidence also suggests that the symbionts are transmitted vertically from one generation of D. sansibarensis to the next. Strict vertical transmission is rare in plants, and usually evolves because the symbionts incur strong fitness benefits to the host plant. The putative benefits of the Dioscorea leaf nodule symbiosis for the plant are so far unknown, but other leaf nodule symbiosis in Rubiaceae and Primulaceae (both dicots) involve the production of potent secondary metabolites that protect the plants against herbivores. The objectives of this proposal are: 1) to establish if the relationship between the host and symbiont is exclusive through the survey of wild D. sansibarensis of Madagascar; 2) to investigate the role and function of the symbionts and 3) establish the life cycle of the symbiosis.