The Ribbon-Helix-Helix Domain Protein CdrS Regulates the Tubulin Homolog ftsZ2 To Control Cell Division in Archaea

Abstract

Precise control of the cell cycle is central to the physiology of all cells. In prior work we demonstrated that archaeal cells maintain a constant size; however, the regulatory mechanisms underlying the cell cycle remain unexplored in this domain of life. Here, we use genetics, functional genomics, and quantitative imaging to identify and characterize the novel CdrSL gene regulatory network in a model species of archaea. We demonstrate the central role of these ribbon-helix-helix family transcription factors in the regulation of cell division through specific transcriptional control of the gene encoding FtsZ2, a putative tubulin homolog. Using time-lapse fluorescence microscopy in live cells cultivated in microfluidics devices, we further demonstrate that FtsZ2 is required for cell division but not elongation. The cdrS-ftsZ2 locus is highly conserved throughout the archaeal domain, and the central function of CdrS in regulating cell division is conserved across hypersaline adapted archaea. We propose that the CdrSL-FtsZ2 transcriptional network coordinates cell division timing with cell growth in archaea. IMPORTANCE Healthy cell growth and division are critical for individual organism survival and species long-term viability. However, it remains unknown how cells of the domain Archaea maintain a healthy cell cycle. Understanding the archaeal cell cycle is of paramount evolutionary importance given that an archaeal cell was the host of the endosymbiotic event that gave rise to eukaryotes. Here, we identify and characterize novel molecular players needed for regulating cell division in archaea. These molecules dictate the timing of cell septation but are dispensable for growth between divisions. Timing is accomplished through transcriptional control of the cell division ring. Our results shed light on mechanisms underlying the archaeal cell cycle, which has thus far remained elusive.

CdrS is a global transcriptional regulator influencing cell division inHaloferax volcanii

“…Consistent with this, our findings implicate CdrS as an activator of vitamin B12 (cobalamin) biosynthesis in H. volcanii (Supplementary Table 1B), which has previously been noted to be under the regulatory network of the transcriptional regulator TrmB, a regulator of sugar metabolism in H. salinarum (55). Expression of the CdrS homolog in H. salinarum is itself regulated in response to oxidative stress (56). These results suggest that CdrS could take part in regulating division and envelope-related functions in response to multiple global response pathways.…”

“…We have identified a small protein-encoding gene (HVO_0582), adjacent to ftsZ2 in H. volcanii, which is highly transcribed according to a transcription start site analysis (38) (Figure 1). Based on the results reported here and in accordance with the concurrent study of its homologue from Halobacterium salinarum (39), we termed this protein CdrS (cell division regulator -short). The cdrS-ftsZ2 locus is well conserved across Euryarchaeota, especially within the class of Halobacteria.…”

“…Our results are consistent with a hypothesis that there is substantial post-transcriptional regulation in the regulatory systems involving CdrS, and this may extend to other regulatory pathways in H. volcanii. In Haloarchaea, the function of CdrS appears to be conserved in relation to the regulation of cell division(56). Our combined results suggest that CdrS is part of a regulatory network and controls the cell division apparatus and other downstream gene products in response to several conditions or stresses and via other transcription regulators.…”

“…), which is also encoded in an operon together with FtsZ2, can be deleted (56); H. salinarum CdrS appears not to be involved in regulation of DacZ and proteasome proteins, which might explain its non-essentiality.…”

“…As the FtsZ-based cell division apparatus is dispensable in H. volcanii(15), the essential function of the Haloferax CdrS might lie in regulation of the essential DacZ and proteasome proteins. Interestingly, the CdrS homolog in H. salinarum (HbaCdrS, VNG0194H), which is also encoded in an operon together with FtsZ2, can be deleted(56); H. salinarum CdrS appears not to be involved in regulation of DacZ and proteasome proteins, which might explain its non-essentiality. We noted a general low correlation between ChIP-Seq, proteome and transcriptome datasets.…”