1887

Abstract

sp. strain PCC 7120 is a filamentous cyanobacterium that differentiates nitrogen-fixing heterocysts when available combined nitrogen is limiting. Growth under diazotrophic conditions results in a mixture of ‘new’ (recently differentiated) and ‘old’ (mature) heterocysts. The microoxic environment present in heterocysts makes the interpretation of gene expression using oxygen-dependent fluorophores, including GFP, difficult. The work presented here evaluates the transcriptional dynamics of three developmental genes in mature heterocysts utilizing EcFbFP, a flavin mononucleotide-dependent fluorophore, as the reporter. Expression of both GFP and EcFbFP from the heterologous promoter showed that, although GFP and EcFbFP fluoresced in both vegetative cells and new heterocysts, only EcFbFP fluoresced in old heterocysts. A transcriptional fusion of EcFbFP to the late-stage heterocyst-specific promoter displayed continued expression beyond the cessation of GFP fluorescence in heterocysts. Promoter fusions of the master regulator of differentiation, , and its inhibitors, and , to GFP and EcFbFP were visualized to determine their role(s) in heterocyst function after morphogenesis. The expression of and was found to persist beyond the completion of development in most heterocysts, whereas expression ceased. These data are consistent with a model of heterocyst patterning in which is involved in pattern formation, is required for pattern maintenance, and is needed for all stages of development.

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2014-09-01
2019-11-17
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