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

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Abstract
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 Δ devT 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 Δ devT 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 Δ devT 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 Δ devT 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.