A chromosome-encoded ParMR system that forms membrane-bound filaments regulating cell shape in Cyanobacteria

Actin-like protein filaments are essential for bacterial intracellular organization. For example, ParMRC systems are well known to segregate newly replicated plasmids using actin-like filaments of ParM, the DNA-binding protein ParR, and the parC DNA element. Multicellular cyanobacteria like Anabaena, have a chromosomal ParMR system with potential implications in chromosome segregation. However, its precise function remained unclear.
Surprisingly, we discovered that the ParMR system is not involved in DNA segregation, but instead comprises a novel cytoskeletal system of membrane-bound filaments that regulates cell shape. Evolutionary analysis revealed that these new functions co-evolved with a modification of the cyanobacterial Min system that we found to control ParM polymerization, thereby establishing a link between cell shape regulation and cell division. Our research not only reveals a new cytoskeletal system in Cyanobacteria, but also shed light on how protein functions can change and be modified during evolution.