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Global Gene Expression Patterns of Nostoc punctiforme in Steady-State Dinitrogen-Grown Heterocyst-Containing Cultures and at Single Time Points during the Differentiation of Akinetes and Hormogonia ^,

Section of Microbiology, University of California, Davis, California 95616,¹ Department of Biology, California State University, Northridge, California 91330²

Received 9 March 2007/ Accepted 26 April 2007

The vegetative cells of the filamentous cyanobacterium Nostoc punctiforme can differentiate into three mutually exclusive cell types: nitrogen-fixing heterocysts, spore-like akinetes, and motile hormogomium filaments. A DNA microarray consisting of 6,893 N. punctiforme genes was used to identify the global transcription patterns at single time points in the three developmental states, compared to those in ammonium-grown time zero cultures. Analysis of ammonium-grown cultures yielded a transcriptome of 2,935 genes, which is nearly twice the size of a soluble proteome. The NH₄⁺-grown transcriptome was enriched in genes encoding core metabolic functions. A steady-state N₂-grown (heterocyst-containing) culture showed differential transcription of 495 genes, 373 of which were up-regulated. The majority of the up-regulated genes were predicted from studies of heterocyst differentiation and N₂ fixation; other genes are candidates for more detailed genetic analysis. Three days into the developmental process, akinetes showed a similar number of differentially expressed genes (497 genes), which were equally up- and down-regulated. The down-regulated genes were enriched in core metabolic functions, consistent with entry into a nongrowth state. There were relatively few adaptive genes up-regulated in 3-day akinetes, and there was little overlap with putative heterocyst developmental genes. There were 1,827 differentially transcribed genes in 24-h hormogonia, which was nearly fivefold greater than the number in akinete-forming or N₂-fixing cultures. The majority of the up-regulated adaptive genes were genes encoding proteins for signal transduction and transcriptional regulation, which is characteristic of a motile filament that is poised to sense and respond to the environment. The greatest fraction of the 883 down-regulated genes was involved in core metabolism, also consistent with entry into a nongrowth state. The differentiation of heterocysts (steady state, N₂ grown), akinetes, and hormogonia appears to involve the up-regulation of genes distinct for each state.

Published ahead of print on 4 May 2007.

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