1887

Abstract

sp. strain PCC 7120 is a filamentous cyanobacterium that differentiates nitrogen-fixing heterocysts when fixed nitrogen becomes growth limiting in the medium. The gene (designated herein), located immediately upstream of the master regulator of differentiation , was identified in a genetic screen for mutants unable to grow diazotrophically. Filaments with a mutation in were unable to fix nitrogen or synthesize heterocyst-specific glycolipids, and they fragmented initially to approximately nine cells in length at 24 h after induction of heterocyst development and eventually became unicellular. The fragmentation phenotype could be duplicated in the presence of fixed nitrogen when differentiation of heterocysts was elicited by overexpression of , suggesting that a defect in differentiation, and not a lack of fixed nitrogen in the medium, was the more direct cause of fragmentation. An intact gene was necessary for differentiation of mature heterocysts, but was not required for proper pattern formation, as indicated by a normal pattern of expression of in a mutant. A transcriptional GFP reporter fusion indicated that the level of expression of was low in vegetative cells in both nitrogen-replete and nitrogen-free media, and was induced in heterocysts. appears to play a role in filament integrity and differentiation of proheterocysts into mature heterocysts.

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2007-02-01
2020-10-30
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