A proteolytic pathway coordinates cell division and heterocyst differentiation in the cyanobacterium Anabaena sp. PCC 7120

Abstract

The filamentous, multicellular cyanobacterium Anabaena sp. PCC 7120 ( Anabaena ) is a prokaryotic model for the study of cell differentiation and cell-cell interactions. Upon combined-nitrogen deprivation, Anabaena forms a particular cell type, heterocyst, for aerobic nitrogen fixation. Heterocysts are semiregularly spaced among vegetative cells. Heterocyst differentiation is coupled to cell division, but the underlying mechanism remains unclear. This mechanism could be mediated by the putative protease HetF, which is a divisome component and is necessary for heterocyst differentiation. In this study, by suppressor screening, we identified PatU3, as a negative regulator acting downstream of HetF for cell division and heterocyst development. The inactivation of patU3 restored the capacity of cell division and heterocyst differentiation in the Δ hetF mutant, and overexpression of patU3 inhibited both processes in the wild-type background. We demonstrated that PatU3 was a specific substrate of the protease activity of HetF. Consequently, PatU3 accumulated in the hetF -deficient mutant, which was responsible for the resultant mutant phenotype. The cleavage site of PatU3 by HetF was mapped after the Arg117 residue, whose mutation made PatU3 resistant to HetF processing, and mimicked the effect of hetF deletion. Our results provided evidence that HetF regulated cell division and heterocyst differentiation by controlling the inhibitory effects of PatU3. This proteolytic pathway constituted a mechanism for the coordination between cell division and differentiation in a prokaryotic model used for studies on developmental biology and multicellularity.

Control of Cell Size by c-di-GMP Requires a Two-Component Signaling System in the Cyanobacterium Anabaena sp. Strain PCC 7120

“…The protein concentration was determined by Bradford assay ( 45 ). Western blotting was carried out using a procedure as described ( 46 ). The DGC activity assay was analyzed as previously described ( 29 , 47 ).…”

“…Microscopic images were captured by using a SDPTOP EX30 microscope and processed using ImageJ without deconvolution as described ( 46 ). For cell size analysis, microscopic images were taken when optical density of a culture reached 0.3 to 0.5 at OD 750 (exponential growth phase).…”

HetF defines a transition point from commitment to morphogenesis during heterocyst differentiation in the cyanobacterium Anabaena sp. PCC 7120

“…We showed previously that the accumulation of the PatU3 protein was observed concomitantly with a defect in cell division in the ΔhetF mutant when either nitrate or ammonium was used as a nitrogen source under different light intensities (Xing et al, 2022).…”

“…One of the coupling mechanisms between cell division and heterocyst differentiation is mediated by HetF, a protein required for both processes (Xing et al, 2021(Xing et al, , 2022. HetF, a member of the divisome complex, acts as a cysteine protease with PatU3 as a substrate (Xing et al, 2022).…”

“…One of the coupling mechanisms between cell division and heterocyst differentiation is mediated by HetF, a protein required for both processes (Xing et al, 2021(Xing et al, , 2022. HetF, a member of the divisome complex, acts as a cysteine protease with PatU3 as a substrate (Xing et al, 2022). PatU3 inhibits not only heterocyst differentiation but also alternative division sites together with the Min system to ensure cell division symmetry (Liu et al, 2023).…”