GROWTH POLE RING protein forms a 200-nm-diameter ring structure essential for polar growth and rod shape in Agrobacterium tumefaciens

Abstract

Polar growth in Agrobacterium pirates and repurposes well-known bacterial cell cycle proteins, such as FtsZ, FtsA, PopZ, and PodJ. Here we identify a heretofore unknown protein that we name GROWTH POLE RING (GPR) due to its striking localization as a hexameric ring at the growth pole during polar growth. GPR also localizes at the midcell late in the cell cycle just before division, where it is then poised to be precisely localized at new growth poles in sibling cells. GPR is 2,115 aa long, with two N-terminal transmembrane domains placing the bulk of the protein in the cytoplasm, N-and C-terminal proline-rich disordered regions, and a large 1,700-aa central region of continuous α-helical domains. This latter region contains 12 predicted adjacent or overlapping apolipoprotein domains that may function to sequester lipids during polar growth. Stable genetic deletion or riboswitch-controlled depletion results in spherical cells that grow poorly; thus, GPR is essential for wild-type growth and morphology. As GPR has no predicted enzymatic domains and it forms a distinct 200-nm-diameter ring, we propose that GPR is a structural component of an organizing center for peptidoglycan and membrane syntheses critical for cell envelope formation during polar growth. GPR homologs are found in numerous Rhizobiales; thus, our results and proposed model are fundamental to understanding polar growth strategy in a variety of bacterial species.Agrobacterium | bacterial polar growth | apolipoprotein | rod-shape morphology | GROWTH POLE RING protein

Tol-Pal system and Rgs proteins interact to promote unipolar growth and cell division inSinorhizobium meliloti

“…RgsE-depleted cells were irregularly shaped with strong curvature. These cells were morphologically similar to the A. tumefaciens GPR-depleted cells (16). Depletion of RgsS resulted in formation of short, partially branched cell filaments with bulges along the filaments, which may represent swollen septation sites.…”

“…2A). RgsE is a homolog of the A. tumefaciens growth pole ring protein GPR, recently reported to promote polar growth in this organism (16). Noteworthy, RgsB, RgsD and RgsG were previously identified as putative interaction partners of RgsM, and RgsG as putative interaction partner of RgsP (12).…”

“…RgsE is a 2089 amino acid protein with up to ten Apolipoprotein A1/A4/E domains, homology to SMC chromosome segregation protein (coiled-coil regions) and 42 % of sequence identity to A. tumefaciens GPR (Atu1348) (16). Overexpression of rgsE in cells cultured in TY broth resulted in cell branching, similar to the morphology of A. tumefaciens GPR-overproducing cells.…”

“…RgsE is a homolog of A. tumefaciens GPR, essential for pole formation in this bacterium (16). RgsE homologs were found in all Rhizobiales families and more distant homologs were detected in Emcibacterales and Rhodospirillales.…”

“…Cells depleted for these proteins produce branches originating from the septal site (14). The exceptionally large growth pole ring protein GPR, which localizes to the growing cell pole, was shown to be required for normal polar growth and rod cell morphology in A. tumefaciens (16). Its overproduction caused formation of ectopic growth zones and cell branching, thus this protein was proposed to constitute a structural component of an organizing center for PG synthesis during polar growth (16).…”