The elongasome, or the Rod complex, orchestrates lateral peptidoglycan (PG) synthesis in many rod-shaped bacteria. It consists of the actin-like protein MreB, the PG synthase RodA-PBP2 complex, as well as MreCD and RodZ. Although the loss or disruption of any elongasome component results in a loss of rod shape, previous studies found that a constitutively active RodA-PBP2 complex can partially bypass the requirement of MreCD and RodZ for lateral PG synthesis and restore rod shape. However, how MreB is connected to RodA-PBP2 under this situation and whether this linkage is important for elongasome activity in wild-type cells remain unknown. Here, we report the isolation of additional RodA and PBP2 variants that can partially compensate for the absence of MreCD and RodZ in lateral PG synthesis. Taking advantage of these mutants and guided by an AlphaFold 3 structural model of the elongasome complex, we discover that both the cytoplasmic region of PBP2 and the C-terminal tail of RodA interact with MreB. Moreover, disruption of these interactions results in a loss of rod shape, indicating that the interaction between MreB and RodA-PBP2 is critical for elongasome function. Taken together, our results uncover how the MreB cytoskeleton is coupled to RodA-PBP2 to organize lateral PG synthesis. These findings provide mechanistic insights into cell wall biogenesis in bacteria and offer strategies for the development of new antibiotics targeting the elongasome.

The tubulin‐like protein FtsZ assembles into the Z ring that leads to the assembly and activation of the division machinery in most bacteria. ZapA, a widely conserved protein that interacts with FtsZ, plays a pivotal role in organizing FtsZ filaments into a coherent Z ring. Previous studies revealed that ZapA forms a dumbbell‐like tetramer that binds cooperatively to FtsZ filaments and aligns them in parallel, leading to the straightening and organization of FtsZ filament bundles. However, how ZapA interacts with FtsZ remains obscure. Here, we reveal that ZapA uses a two‐pronged mechanism to interact with FtsZ to facilitate Z ring formation in Escherichia coli. We find that mutations affecting surface‐exposed residues at the junction between adjacent FtsZ subunits in a filament as well as in an N‐terminal motif of FtsZ weaken its interaction with ZapA in vivo and in vitro, indicating that ZapA binds to these regions of FtsZ. Consistent with this, ZapA prefers FtsZ polymers over monomeric FtsZ molecules and site‐specific crosslinking confirmed that the dimer head domain of ZapA is in contact with the junction of FtsZ subunits. As a result, disruption of the putative interaction interfaces between FtsZ and ZapA abolishes the midcell localization of ZapA. Taken together, our results suggest that ZapA tetramers grab the N‐terminal tails of FtsZ and bind to the junctions between FtsZ subunits in the filament to straighten and crosslink FtsZ filaments into the Z ring.