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Journal of Bacteriology, October 2009, p. 6059-6066, Vol. 191, No. 19
0021-9193/09/$08.00+0     doi:10.1128/JB.01271-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Mutual Regulation of ntcA and hetR during Heterocyst Differentiation Requires Two Similar PP2C-Type Protein Phosphatases, PrpJ1 and PrpJ2, in Anabaena sp. Strain PCC 7120 {triangledown}

Jichan Jang ,1,{dagger},{ddagger} Lei Shi,2,{dagger} Hui Tan,2 Annick Janicki,1 and Cheng-Cai Zhang1,2*

Aix-Marseille Université and Laboratoire de Chimie Bactérienne, CNRS-UPR9043, Institut de Biologie Structurale et Microbiologie, 13402 Marseille, France,1 State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, People's Republic of China2

Received 10 September 2008/ Accepted 10 July 2009

The filamentous cyanobacterium Anabaena sp. strain PCC 7120 can form heterocysts for N2 fixation. Initiation of heterocyst differentiation depends on mutual regulation of ntcA and hetR. Control of hetR expression by NtcA is partially mediated by nrrA, but other factors must be involved in this regulation. Anabaena has two closely related PP2C-type protein phosphatases, PrpJ1 (formerly PrpJ) and PrpJ2; PrpJ1 is involved in heterocyst maturation. In this study, we show that PrpJ2, like PrpJ1, has Mn2+-dependent phosphatase activity. We further demonstrate that whereas prpJ2 is dispensable for cell growth under different nitrogen regimens tested, a double mutant with both prpJ1 and prpJ2 disrupted did not initiate heterocyst differentiation. Ectopic expression of hetR in the double mutant could rescue the failure to initiate heterocyst development, but the heterocysts formed, like those of a prpJ1 single mutant, were not mature. The expression of prpJ2 was enhanced during heterocyst development, and the upregulation of the gene was directly under the control of NtcA. Upregulation of both ntcA and hetR was affected in the double mutant. We propose that PrpJ1 and PrpJ2 together are required for mutual regulation of ntcA and hetR and are thus involved in regulation of the initiation of heterocyst differentiation.

* Corresponding author. Mailing address: Laboratoire de Chimie Bactérienne, 31 chemin Joseph Aiguier, 13402 Marseille cedex 20, France. Phone: 33-4-91164069. Fax: 33-4-91718914. E-mail: cczhang{at}ifr88.cnrs-mrs.fr

{triangledown} Published ahead of print on 24 July 2009.

{dagger} J.J. and L.S. contributed equally to this work.

{ddagger} Present address: Institut Pasteur of Korea, Seoul, Korea.

Journal of Bacteriology, October 2009, p. 6059-6066, Vol. 191, No. 19
0021-9193/09/$08.00+0     doi:10.1128/JB.01271-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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