FIG. 6.

Model of the flagellar transcriptional cascade in X. campestris pv. campestris. Flagellar genes can be placed in three temporal classes according to the type of promoter recognized by the different sigma factors. Class I proteins RpoN2 (σ⁵⁴) and the cognate activator FleQ are the master regulator directing the expression of class II genes. Early FlgM transcribed from a class I promoter inhibits class II sigma factor FliA until completion of the production of class II proteins and assembly of the F-T3SS-basal body-hook structure. Late (class III) genes belong to the FliA (σ²⁸) regulons. Flagellar filament, cap proteins, and motility regulatory proteins are identified. Late FlgM acts as a final brake to the whole process. The promoter consensus based on the type II and type III flagellar genes of X. campestris pv. campestris is indicated at the top.