Seminars

The cyanobacterium Nostoc punctiforme has an extensive array of phenotypic traits, which makes it an unusual experimental system. Of specific interest is the observation that its vegetative cells have three developmental fates, dependent on environmental signals: nitrogen-fixing heterocysts; spore-like akinetes; and motile hormogonium filaments.  N. punctiforme can also fix nitrogen in free-living and plant-associated symbiotic growth states. Hormogonia are the infective units and heterocysts the functional units of symbiotic association.  Our studies focus on hormogonium and heterocyst differentiation.  Abrupt nitrogen starvation and plant factors will induce the differentiation of both hormogonia and heterocysts; the plant factors override the nitrogen starvation response in both cases. Following nitrogen starvation, specific temporal points are encountered where cellular fates are determined. Regulatory elements are being identified that are associated with the decision-making events.