Functional dissection of Wag31 domains for septal recruitment and polar distribution during the cell cycle.

Bacterial cell morphogenesis is controlled by the synthesis and organization of peptidoglycan and driven by multi-protein complexes such as the divisome and elongasome. Here we investigate the role of the DivIVA homologue, Wag31, the elongasome scaffold essential for polar growth in . Conditional depletion of Wag31 results in viable but coccoid-shaped cells, showing that Wag31 is essential for rod shape maintenance. Our structural phylogenetic analyses of DivIVA homologues revealed that in , unlike , an intrinsically disordered region spatially separates the N-terminal lipid-binding domain (LBD) from the C-terminal coiled-coil domain (CCD). We show that the LBD is necessary and sufficient for septum localization, independent of its membrane-binding properties, while the CCD domain mediates self-interaction and polar accumulation. Our findings suggest that Wag31 is recruited specifically to the septum through protein-protein interactions, priming the future pole and allowing for a timely divisome-elongasome transition at cytokinesis. Once the pole is formed the self-aggregative properties of the C-terminal CCD dominate and form a stable structure that likely organizes the pole for cell wall biosynthesis.