FIGURE 2.

Progress of heterocyst differentiation. The scheme represents the process of differentiation of a filament of heterocyst-forming cyanobacteria with the roles of the main genes involved. Darker green means more fixed nitrogen in a cell. Low nitrogen induces NtcA expression, which, in turn, activates HetR, the master regulator of heterocyst differentiation. Yellow is a cell committing to differentiation and producing a gradient of PatS inhibiting the action of HetR in neighboring cells. Orange is a differentiated cell, a heterocyst, producing fixed nitrogen and a gradient of the inhibitor HetN and receiving carbon from vegetative cells. Reproduced from Di Patti et al. (2018), CC BY 4.0 license.