The Small Regulatory Antisense RNA PilR Affects Pilus Formation and Cell Motility by Negatively Regulating in sp. PCC 6803.

Pili are found on the surface of many bacteria and play important roles in cell motility, pathogenesis, biofilm formation, and sensing and reacting to environmental changes. Cell motility in the model cyanobacterium sp. PCC 6803 relies on expression of the putative operon. In this study, we identified the antisense RNA PilR encoded in the noncoding strand of the prepilin-encoding gene . Analysis of overexpressor [PilR(+)] and suppressor [PilR(-)] mutant strains revealed that PilR is a direct negative regulator of PilA11 protein. Although overexpression of PilR did not affect cell growth, it greatly reduced levels of mRNA and protein and decreased both the thickness and number of pili, resulting in limited cell motility and small, distinct colonies. Suppression of PilR had the opposite effect. A hypothetical model on the regulation of operon expression by PilR was proposed. These results add a layer of complexity to the mechanisms controlling gene expression and cell motility, and provide novel insights into how sRNA and the intergenic region secondary structures can work together to discoordinatly regulate target gene in an operon in cyanobacterium.