DnaK1-mediated regulation of phototactic motility in Synechococcus elongatus UTEX 3055

Cyanobacterial phototaxis relies on type IV pili (T4P); yet, how light signals are transmitted to the T4P motor remains unresolved. Here, we identify the molecular chaperone DnaK1 as an important regulator of phototactic motility in Synechococcus elongatus UTEX 3055. DnaK1 interacts with the phototaxis regulator PixG_Se and the T4P extension ATPase PilB, and loss of dnaK1 impairs phototactic motility. Mutations in dnaJ1 impair phototaxis, and a partially segregated grpE mutant shows a similar but milder defect, suggesting that the DnaK1-DnaJ1-GrpE system may contribute to this process. Fluorescence imaging shows that DnaK1, PixG_Se, and PilB have similar polar localization patterns. Based on these findings, we propose a working model in which DnaK1 may facilitate the assembly or stability of phototaxis-associated T4P complexes, thereby providing a potential mechanistic link between the phototaxis signaling module and T4P motor activity. These findings establish a link between DnaK1 and the phototaxis machinery, highlighting a potential role for molecular chaperones in coupling light-sensing pathways to T4P-mediated motility.