Uncoupling Flagellar Gene Expression from Flagellar Assembly

How do cells sense the assembly status of "extracellular" structures and react to changes in assembly status? Flagellar assembly is a temporal process, requiring secretion of flagellar subunits via a dedicated secretion apparatus through the base of the growing structure and incorporated at its tip. The secretion apparatus associated with the flagellum belongs to the type III secretion (T3S) family. Other T3S systems are associated with an injectisome, which injects virulence determinants into host cells to facilitate pathogenesis. The bacterial cell is posed with a major problem in sensing the assembly status of a flagellum due to its external nature and length. How bacteria overcome this problem has lead to flagellar assembly, becoming a leading model system used to study the coupling of gene expression to macromolecular structure assembly. Substrate recognition by the T3S secretion apparatus is facilitated by the T3S chaperones. Two flagellar T3S chaperones FlgN and FliT in Salmonella enterica are bi-functional also sensing the progression of flagellar assembly, feeding the perceived signals back into the system at the level of flagellar gene expression. <P>
Our current objectives are to identify how FlgN and FliT regulate flagellar gene expression and to determine the effect of removing the regulation of flagellar gene expression by the T3S chaperones with respect to flagellar gene expression. <P>We aim to achieve our goals by isolating and characterizing mutants in the regulatory functions of FlgN and FliT. Regulatory mutants will then be used in combination with other flagellar mutations to study flagellar gene expression with respect to time in bioluminescence based real time growth assays.