Project description:How cellular checkpoints couple the orderly assembly of macromolecular machines with cell cycle progression is poorly understood. The alpha-proteobacterium Caulobacter crescentus assembles a single polar flagellum during each cell cycle. We discovered that expression of multiple flagellin transcripts is licensed by a translational checkpoint responsive to a dual input signal: a secretion-competent hook-basal-body (HBB) structure and a surge in the FlaF secretion chaperone during cytokinesis, instructed by the cell cycle circuitry. We find that the unorthodox FljJ flagellin, one of six flagellin paralogs, acts as checkpoint linchpin, binding both FlaF and the FlbT translational regulator. FljJ recruits FlbT to inhibit translation at the 5’ untranslated region in other flagellin transcripts before HBB assembly. Once FlaF is synthesized and stabilized, it directs FljJ secretion through the HBB, thereby separating FlbT from its co-activator and relieving translational inhibition. The FlbT/FlaF pair is wide-spread and functional properties are conserved in alpha-proteobacteria, including pathogens.
Project description:How cellular checkpoints couple the orderly assembly of macromolecular machines with cell cycle progression is poorly understood. The alpha-proteobacterium Caulobacter crescentus assembles a single polar flagellum during each cell cycle. We discovered that expression of multiple flagellin transcripts is licensed by a translational checkpoint responsive to a dual input signal: a secretion-competent hook-basal-body (HBB) structure and a surge in the FlaF secretion chaperone during cytokinesis, instructed by the cell cycle circuitry. We find that the unorthodox FljJ flagellin, one of six flagellin paralogs, acts as checkpoint linchpin, binding both FlaF and the FlbT translational regulator. FljJ recruits FlbT to inhibit translation at the 5’ untranslated region in other flagellin transcripts before HBB assembly. Once FlaF is synthesized and stabilized, it directs FljJ secretion through the HBB, thereby separating FlbT from its co-activator and relieving translational inhibition. The FlbT/FlaF pair is wide-spread and functional properties are conserved in alpha-proteobacteria, including pathogens.
Project description:Vibrio campbellii is a gram-negative bacterial pathogen that is both free-living and a pathogen of marine organisms and exhibits swimming motility via a single, polar flagellum. Swimming motility is a critical virulence factor in V. campbellii pathogenesis, and disruption of the flagellar motor significantly decreases host mortality. However, while V. campbelli encodes homologs of flagellar and chemotaxis genes conserved by other members of the Vibrionaceae, the regulatory network governing these genes have not been explored. We systematically deleted all 63 known flagellar and chemotaxis genes in V. campbellii and examined their effects on motility compared to their homologs in other Vibrios. We specifically focused on assessing the roles of the core flagellar regulators of the flagellar regulatory hierarchy established in other Vibrios: rpoN, flrA, flrC, and fliA. Although V. campbellii transcription of flagellar and chemotaxis genes is governed by a multi-tiered regulatory hierarchy similar to other Vibrios, we observed two critical differences: the σ54-dependent regulator FlrA is dispensable for motility, and Class II gene expression is independent of σ54 regulation. Our genetic and phenotypic dissection of the V. campbellii flagellar regulatory network highlights the differences that have evolved in flagellar regulation across the Vibrionaceae.