FliAdependent

FliA-dependent refers to genes whose transcription requires the alternative sigma factor FliA (sigma 28) in certain bacteria, most notably in Escherichia coli and Salmonella enterica. FliA directs RNA polymerase to promoters that control late-stage flagellar genes, which are activated after the basal body and hook structure have begun to form.

The activity of FliA is tightly regulated by the flagellar master regulator FlhDC and by the anti-sigma factor FlgM. FlgM binds FliA and prevents transcription of FliA-dependent genes until the completed hook-basal body complex is able to secrete FlgM via the type III secretion system. Once FlgM is removed, FliA can initiate transcription of its regulon, enabling the final steps of flagellum assembly.

FliA-dependent genes encode components of the flagellum that are expressed later in the assembly process. These typically include the filament subunit flagellin (FliC), hook-associated and cap proteins, and motor or stator components such as MotA and MotB, as well as various assembly and export factors required for a functional flagellum. The promoters of these genes are recognized specifically by RNA polymerase in complex with FliA, and their expression links to the completion of earlier flagellar structures.

The set of FliA-dependent genes can vary among species, but the overarching pattern is conserved: FliA drives the transcription of late-assembly, motility-related genes necessary for a functional flagellum. Disruption of FliA signaling or its regulon often results in impaired motility and chemotaxis.