HetF protein is a new divisome component in a filamentous and developmental cyanobacterium

Abstract

Bacterial cell division, with a few exceptions, is driven by FtsZ through a treadmilling mechanism to remodel and constrict the rigid peptidoglycan (PG) layer. Yet, different organisms may differ in the composition of the cell-division complex (divisome). In the filamentous cyanobacterium Anabaena PCC 7120, hetF is required for the initiation of the differentiation of heterocysts, cells specialized in N2-fixing cells under combined nitrogen deprivation. In this study, we demonstrate that hetF is expressed in vegetative cells and necessary for cell division in a conditional manner. Under non-permissive conditions, cells of a ΔhetF mutant stop dividing, consistent with increased level of HetF under similar conditions in the wild type. Furthermore, HetF is a membrane protein located at midcell and cell-cell junctions. In the absence of HetF, FtsZ rings are still present in the elongated cells; however, PG remodelling is abolished. This phenotype is similar to that observed with the inhibition of septal PG synthase FtsI. We further reveal that HetF is recruited to or stabilized at the divisome by interacting with FtsI and this interaction is necessary for HetF function in cell division. Our results indicate that HetF is a member of the divisome, and reveal distinct features of the cell-division machinery in cyanobacteria that are of high ecological and environmental importance.Significance StatementCyanobacteria shaped the Earth’s evolutionary history, and are still playing important roles for elementary cycles in different environments. They are consisted of highly diverse species with different cell shape, size and morphology. Although these properties are strongly affected by the process of cytokinesis, the mechanism remains largely unexplored. Using different approaches, we demonstrate that HetF is a new component of the cell division machinery in the filamentous cyanobacterium Anabaena PCC 7120. The common and diverged characteristics of cell division in prokaryotes reflect the evolutionary history of different bacteria, as an adaptive measure to proliferate under certain environmental conditions. As a protein for cell differentiation, the recruitment of HetF to the septum illustrates such an adaptive mechanism for cyanobacteria.

The developmental regulator PatD modulates assembly of the cell‐division protein FtsZ in the cyanobacterium Anabaena sp. PCC 7120

“…Because PatD influenced cell size and appeared to interfere with cell division, we tested whether PatD affects the subcellular localization of FtsZ. For that, we transferred a ftsZ‐cfp gene construct (Xing et al ., 2021), encoding a version of FtsZ C‐terminally fused to the cyan fluorescent protein, to the wild‐type strain and to strains M1550 ( patD mutant) and OE1550 (P petE ‐ patD in a replicative plasmid), replacing the native chromosomal ftsZ gene. In the wild‐type background, CFP fluorescence formed ring structures at midcell positions, both in filaments using nitrate and in vegetative cells of filaments incubated under diazotrophic conditions (Fig.…”

“…Plasmids pNiSG, encoding a StrepTag‐GFP protein fusion, and pNiSG‐ patD , encoding a StrepTag‐PatD‐GFP fusion expressed from the nickel‐inducible promoter P nrsB were introduced into Anabaena by conjugation to create strains NiSG and NiSG‐PatD, respectively. The plasmid p ftsZ ‐ cfp (Xing et al ., 2021), used to replace the native ftsZ gene by a ftsZ ‐ cfp fusion gene was transferred to wild‐type Anabaena and strain M1550 by conjugation to create strains WT/FtsZ‐CFP and M1550/FtsZ‐CFP, respectively. Plasmid pP petE ‐ patD was transferred to strain WT/FtsZ‐CFP to create OE1550/FtsZ‐CFP.…”

“…Thus, the presence of extra copies of oriC leads to the formation of multiple contiguous heterocysts and downregulation of the DNA polymerase gene polA leads to the formation of double heterocysts (Zhou et al ., 2011; Xing et al ., 2020). Also, regulation of ftsZ at both transcriptional and post‐transcriptional levels has been described to take place during the differentiation process (Kuhn et al ., 2000; Sakr et al ., 2006a,b; Valladares et al ., 2020), and HetF, a putative protease, has been recently reported to be involved not only in heterocyst differentiation but also in cell division (Xing et al ., 2021). PatA, a regulator required for the differentiation of intercalary heterocysts, has been described to localize at midcell and interact with ZipN, a major FtsZ‐tether to the cytoplasmic membrane, causing Z‐ring destabilization and inhibition of cell division in the differentiating heterocysts (Young‐Robbins et al ., 2010; Valladares et al ., 2020).…”