The Ser/Thr Kinase PknH Is Essential for Maintaining Heterocyst Pattern in the Cyanobacterium sp. Strain PCC 7120.

In the filamentous cyanobacterium sp. strain, PCC 7120, heterocysts (which are nitrogen-fixing cells) are formed in the absence of combined nitrogen in the medium. Heterocysts are separated from one another by 10 to 15 vegetative cells along the filaments, which consist of a few hundred of cells. is necessary for heterocyst differentiation; and and , expressed in heterocysts, play important roles in heterocyst pattern formation by laterally inhibiting the expression of in adjacent cells. The results of this study indicated that , which encodes a Ser/Thr kinase, was also involved in heterocyst pattern formation. In the mutant, the heterocyst pattern was normal within 24 h after nitrogen deprivation, but multiple contiguous heterocysts were formed from 24 to 48 h. A time-lapse analysis of reporter strains harboring a fusion between and the promoter indicated that was required to suppress expression in cells adjacent to the preexisting heterocysts. These results indicated that was necessary for the lateral inhibition of heterocyst differentiation to maintain the heterocyst pattern.