The hetZ gene indirectly regulates heterocyst development at the level of pattern formation in Anabaena sp. strain PCC 7120

<div class="line" id="line-5"> Multicellular development requires the careful orchestration of gene expression to correctly create and position specialized cells. In the filamentous cyanobacterium <i> Anabaena </i> sp. strain PCC 7120, nitrogen&hyphen;fixing heterocysts are differentiated from vegetative cells in a reproducibly periodic and physiologically relevant pattern. While many genetic factors required for heterocyst development have been identified, the role of HetZ has remained unclear. Here, we present evidence to clarify the requirement of <i> hetZ </i> for heterocyst production and support a model where HetZ functions in the patterning stage of differentiation. We show that a clean, nonpolar deletion of <i> hetZ </i> fails to express the developmental genes <i> hetR </i> , <i> patS </i> , <i> hetP </i> and <i> hetZ </i> correctly and fails to produce heterocysts. Complementation and overexpression of <i> hetZ </i> in a <i> hetP </i> mutant revealed that <i> hetZ </i> was incapable of bypassing <i> hetP </i> , suggesting that it acts upstream of <i> hetP </i> . Complementation and overexpression of <i> hetZ </i> in a <i> hetR </i> mutant, however, demonstrated bypass of <i> hetR </i> , suggesting that it acts downstream of <i> hetR </i> and is capable of bypassing the need for <i> hetR </i> for differentiation irrespective of nitrogen status. Finally, protein&ndash;protein interactions were observed between HetZ and HetR, Alr2902 and HetZ itself. Collectively, this work suggests a regulatory role for HetZ in the patterning phase of cellular differentiation in <i> Anabaena </i> .</div>