A molecular regulatory cascade of heterocyst differentiation in cyanobacteria

• Published in: Journal of plant research Vol. 119; p. 177
• Main Authors: Ehira, S, Ohmori, M
• Format: Journal Article
• Language: English
• Published: 01.12.2006
• Subjects: Cyanobacteria; Cyanophyta
• ISSN: 0918-9440

Heterocysts are terminally differentiated cells of cyanobacteria that are capable of fixing atmospheric nitrogen. Upon limitation of combined nitrogen in the medium, particular vegetative cells change their form into heterocysts with a regular spacing of 10 to 15 cells. NrrA, a nitrogen-responsive response regulator, was shown to be required for the upregulation of hetR, which is the master gene regulating heterocyst development. The use of the nitrogen-responsive transcription initiation sites for the hetR gene depended upon NrrA. NrrA bound specifically to the promoter region of hetR in vitro. Extra copies of nrrA on a plasmid caused a multiple contiguous heterocysts phenotype, the same phenotype as extra copies of hetR. NrrA is considered to regulate the expression of hetR directly in vivo. The expression of nrrA depends on NtcA, which is the global nitrogen regulator in cyanobacteria. A molecular cascade is proposed whereby NtcA upregulates the expression of nrrA upon limitation of combined nitrogen in the medium and then NrrA upregulates the expression of hetR, leading to heterocyst differentiation.