Investigating the Role of HmpF in Regulating Hormogonium Motility in Nostoc punctiforme

The goal of this project is to identify the genes controlling hormogonium development and motility in the filamentous cyanobacterium Nostoc punctiforme. N. punctiforme forms nitrogen-fixing endosymbioses with several different plants and fungi. To establish these symbioses, facilitate dispersal, and perform phototaxis, N. punctiforme differentiates into motile filaments, known as hormogonia, capable of gliding motility via a modified type 4 pilus (T4P) motor. The T4P motors are located at the cell poles and are activated only at the pole corresponding to the direction of movement. Controlling the coordination of polar T4P activation is the chemotaxis-like Hmp system. Using a transposon screen, the gene designated as hmpF was identified as the transposon insertion site in two independent non-motile mutant strains of N. punctiforme. Conserved genomic proximity of hmpF to known Hmp system genes across filamentous cyanobacteria and similar expression patterns between hmpF and hmpD suggest that hmpF is a component of the Hmp system. The resulting deletion mutant phenotype was distinct from other hmp deletion mutants, but identical to ΔpilB and ΔpilQ. An HmpF-GFP fusion was evaluated with immunofluorescence and HmpF was demonstrated to dynamically localize to the site of active motors, correlating with the direction of movement. The polar localization of HmpF was also shown to reverse in response to light. These results indicate that HmpF is coordinated by the Hmp system and interacts with the T4P motor to control the direction of movement. To further characterize how Hmpf interacts with the other motility systems the localization of HmpF-GFP is currently being investigated in different mutant backgrounds lacking the proteins that are likely to directly interact with HmpF