A histidine pseudokinase modulates polar growth and cell shape in Streptomyces venezuelae

Polar growth and cell shape determination in mycelium-forming Streptomyces bacteria depends on the function of a polarly localised multiprotein complex that directs cell wall synthesis - the polarisome. This complex assembles around the essential cell polarity determinant DivIVA, alongside other largely unknown components. We report here the discovery of a conserved hybrid histidine kinase-like protein, PsmA, that interacts and co-localises with DivIVA at the hyphal tips. Deletion of psmA affects the shape and dynamics of the polarisome, leading to aberrant cell shape and hyphal hyperbranching. PsmA is a pseudokinase that lacks the critical histidine residue in its catalytic core. Our results suggest that PsmA tunes the dynamics and properties of the DivIVA-based polar organelle in streptomycetes in parallel to but not redundantly with Scy and FilP, two coiled-coil proteins known to influence polarisome properties. In summary, PsmA interacts with DivIVA and modulates the integrity of the growth zones at hyphal tips.