Coupling of protein localization and cell movements by a dynamically localized response regulator in Myxococcus xanthus

Myxococcus xanthus cells harbor two motility machineries, type IV pili (Tfp) and the A-engine. During reversals, the two machineries switch polarity synchronously. We present a mechanism that synchronizes this polarity switching. We identify the required for motility response regulator (RomR) as essential for A-motility. RomR localizes in a bipolar, asymmetric pattern with a large cluster at the lagging cell pole. The large RomR cluster relocates to the new lagging pole in parallel with cell reversals. Dynamic RomR localization is essential for cell reversals, suggesting that RomR relocalization induces the polarity switching of the A-engine. The analysis of RomR mutants shows that the output domain targets RomR to the poles and the receiver domain is essential for dynamic localization. The small GTPase MglA establishes correct RomR polarity, and the Frz two-component system regulates dynamic RomR localization. FrzS localizes with Tfp at the leading pole and relocates in an Frz-dependent manner to the opposite pole during reversals; FrzS and RomR localize and oscillate independently. The Frz system synchronizes these oscillations and thus the synchronous polarity switching of the motility machineries

The DevT Protein Stimulates Synthesis of FruA, a Signal Transduction Protein Required for Fruiting Body Morphogenesis in Myxococcus xanthus

Fruiting body formation in Myxococcus xanthus involves three morphologic stages—rippling, aggregation, and sporulation—all of which are induced by the cell surface-associated C-signal. We analyzed the function of the DevT protein, a novel component in the C-signal response pathway. A mutant carrying an in-frame deletion in the devT gene displays delayed aggregation and a cell autonomous sporulation defect, whereas it remains rippling proficient. To further define the function of DevT, the methylation pattern of FrzCD, a cytoplasmic methyl-accepting chemotaxis protein homologue, was examined in the ΔdevT mutant, and we found that DevT is required for methylation of FrzCD during development. Specifically, DevT was found to be required for the C-signal-dependent methylation of FrzCD. The ΔdevT mutant produced wild-type levels of C-signal. However, accumulation of the FruA response regulator protein, which is essential for the execution of the C-signal-dependent responses, was reduced in the ΔdevT mutant. The DevT protein was found to stimulate the developmentally activated transcription of the fruA gene. Epistasis analyses indicate that DevT acts independently of the A- and E-signals to stimulate fruA transcription. These findings suggest that the developmental defects of the ΔdevT mutant are associated with a lack of FruA to ensure a proper response to the C-signal during the aggregation and sporulation stages of development