Molecular analysis of genes in Nostoc punctiforme involved in pilus biogenesis and plant infection.

Hormogonia are the infective agents in many cyanobacterium-plant symbioses. Pilus-like appendages are expressed on the hormogonium surface, and mutations in pil-like genes altered surface piliation and reduced symbiotic competency. This is the first molecular evidence that pilus biogenesis in a filamentous cyanobacterium requires a type IV pilus system.