The roles of chemotaxis-like signal transduction systems in the differentiation and behavior of motile filaments of the cyanobacterium Nostoc punctiforme

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The price of motility in cyanobacteria of the genus Nostoc is the transient differentiation of non-growing filaments called hormogonia. Hormogonia function as active dispersal units, allowing the organisms to exploit a favorable, or escape an inhospitable, habitat. Hormogonia of Nostoc punctiforme are phototactic, as well as chemotactic to exudates of plant partners, with which N. punctiforme forms a nitrogen-fixing symbiotic association. One long-term research goal is to manipulate hormogonium differentiation and behavior in experiments to establish new nitrogen-fixing associations with crop plants. The genome of N. punctiforme contains five loci of genes that encode proteins of chemotaxis-like signal transduction complexes. Among these five loci, one locus is essential for the differentiation of hormogonia and another for phototaxis. The involvement of a chemotaxis-like signal transduction system in regulation of cellular differentiation has precedence, but is rare. A variety of experimental approaches will be used to characterize the chemotaxis-like developmental regulation locus (Che2) and the phototaxis locus (Che4), including mutational analysis to determine the functional requirement for the gene products in each locus, DNA microarrays to identify genes under control of the Che2 locus, and bacterial two hybrid assays and mass spectrometric analyses to identy protein-protein associations in assembly of the signal transduction complexes. The results of these collective experiments will provide information on how the signal transduction complexes are differently organized and localized in cells, and how they may have evolved into different functional roles, especially in the regulation of development. The emerging database will be essential for subsequent manipulation of these symbiotic cyanobacteria for agricultural or bioenergy applications. The project will develop experimental tools and materials that will be immediately available to the scientific community. A graduate student and visiting student will be trained in functional genomics. Two to three undergraduate students will trained each year in microbial genomics, genetics and biochemistry by their participation in short-term, well-defined, undergraduate research projects.