We are interested in the molecular basis of mutualistic interactions between eukaryotic hosts and microbes.  We hope to uncover common strategies governing host-microbe mutualism using a model system, the nitrogen-fixing symbiosis between legume plants and rhizobia.  Additionally, this symbiosis holds tremendous promise for sustainability, as it allows the plants to acquire nitrogen nutrition from a virtually limitless source.  The legume-rhizobia symbiosis is a complex process, culminating in the conversion of individual bacterium into nitrogen-fixing organelles, called symbiosomes, within the host cytoplasm.  We discovered that the intracellular bacterial compartment maintains features of the extracellular space, in that it is the target of host protein secretion.  Our current focus is to address the following two questions: how are host proteins delivered to the symbiosomes, and how these proteins control the development of a successful symbiosis.