Three-dimensional coordination of cell-division site positioning in a filamentous cyanobacterium.

Bacterial cells mostly divide symmetrically. In the filamentous, multicellular cyanobacterium , cell-division planes are aligned vertically relative to the long axis of every single cell. This observation suggests that both the placement and the angle of the division planes are controlled in every single cell so that the filament can grow in one single dimension along the long axis. In this study, we showed that inactivation of encoding a cell-division inhibitor led cells to divide asymmetrically in two dimensions leading to twisted filaments, indicating that PatU3 controls not only the position but also the angle of the division planes. Deletion of the conserved and genes affected cell division symmetry, but not the angle of the division planes. Remarkably, when both and were inactivated, cells could divide asymmetrically over 360° angles in three dimensions across different cellular sections, producing not only cells with irregular sizes, but also branching filaments. This study demonstrated the existence of a system operating in a three-dimensional manner for the control of cell division in . Such a regulation may have been evolved to accommodate multicellular behaviors, a hallmark in evolution.