DevT (Alr4674), resembling a Ser/Thr protein phosphatase, is essential for heterocyst function in the cyanobacterium Anabaena sp. PCC 7120

Abstract

Heterocyst-forming cyanobacteria are able to perform oxygenic photosynthesis and nitrogen fixation simultaneously in the same filament, by restricting the highly O 2 -sensitive nitrogenase to specialized cells, the heterocysts. A remarkable change in morphology and metabolism accompanies the differentiation of heterocysts, which only occurs when no source of combined nitrogen is available. In this study, we characterized DevT (Alr4674), a putative protein phosphatase from Anabaena PCC 7120. Mutants defective in devT are able to form morphologically mature heterocysts, which however cannot fix N 2 , and the mutant cannot survive without a source of combined nitrogen. DevT shows homology to phosphatases of the PPP family and displays a Mn 2+ -dependent phosphatase activity that can be inhibited by phosphatase inhibitors and oxidizing conditions. DevT is constitutively expressed in both vegetative cells and heterocysts, and is not regulated by NtcA. The heterocyst regulator HetR may exert a certain inhibition on the expression of devT. Under diazotrophic growth conditions, DevT protein accumulates specifically in mature heterocysts. Therefore DevT plays a still unknown role in a late essential step of heterocyst differentiation.

The pknH gene restrictively expressed in heterocysts is required for diazotrophic growth in the cyanobacterium Anabaena sp. strain PCC 7120

“…The pknE mutant strain can grow in nitrogen-free medium, although its growth rate is slightly slower than that of the WT, and overexpression of pknE blocks heterocyst differentiation (Saha & Golden, 2011). The devT mutant strain can form morphologically mature heterocysts, but it cannot fix nitrogen (Espinosa et al, 2010). Thus, the phosphorylation of Ser/Thr residues of certain proteins in heterocysts plays important roles in heterocyst differentiation and function, and a phosphorylation network might regulate various aspects of heterocyst development.…”

“…2), and a Ser/Thr protein phosphatase DevT accumulates in mature heterocysts (Espinosa et al, 2010). The pknE mutant strain can grow in nitrogen-free medium, although its growth rate is slightly slower than that of the WT, and overexpression of pknE blocks heterocyst differentiation (Saha & Golden, 2011).…”

The putative phosphatase All1758 is necessary for normal growth, cell size and synthesis of the minor heterocyst-specific glycolipid in the cyanobacterium Anabaena sp. strain PCC 7120

“…Alr0117 and HepK (All4496) both encode putative two-component system sensory histidine kinases that appear to be involved in the induction of hepA, one of the genes responsible for synthesis of the heterocyst polysaccharide layer (Ning & Xu, 2004;Ramírez et al, 2005;Xu et al, 2003). The manganese-dependent serine/threonine protein phosphatase of the PPP family DevT (Alr4674) accumulates in mature heterocysts, is not regulated by NtcA and appears to have a role in the later steps of heterocyst differentiation (Espinosa et al, 2010). In this study, the isolation and characterization of a gene encoding a putative PP2C-type protein phosphatase, all1758, is described.…”