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Journal of Bacteriology, October 2004, p. 6422-6429, Vol. 186, No. 19
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.19.6422-6429.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

patS Minigenes Inhibit Heterocyst Development of Anabaena sp. Strain PCC 7120

Xiaoqiang Wu, Duan Liu, Martin H. Lee, and James W. Golden^*

Department of Biology, Texas A&M University, College Station, Texas

Received 9 February 2004/ Accepted 2 July 2004

The patS gene encodes a small peptide that is required for normal heterocyst pattern formation in the cyanobacterium Anabaena sp. strain PCC 7120. PatS is proposed to control the heterocyst pattern by lateral inhibition. patS minigenes were constructed and expressed by different developmentally regulated promoters to gain further insight into PatS signaling. patS minigenes patS4 to patS8 encode PatS C-terminal 4 (GSGR) to 8 (CDERGSGR) oligopeptides. When expressed by P_petE, P_patS, or P_rbcL promoters, patS5 to patS8 inhibited heterocyst formation but patS4 did not. In contrast to the full-length patS gene, P_hepA-patS5 failed to restore a wild-type pattern in a patS null mutant, indicating that PatS-5 cannot function in cell-to-cell signaling if it is expressed in proheterocysts. To establish the location of the PatS receptor, PatS-5 was confined within the cytoplasm as a gfp-patS5 fusion. The green fluorescent protein GFP-PatS-5 fusion protein inhibited heterocyst formation. Similarly, full-length PatS with a C-terminal hexahistidine tag inhibited heterocyst formation. These data indicate that the PatS receptor is located in the cytoplasm, which is consistent with recently published data indicating that HetR is a PatS target. We speculated that overexpression of other Anabaena strain PCC 7120 RGSGR-encoding genes might show heterocyst inhibition activity. In addition to patS and hetN, open reading frame (ORF) all3290 and an unannotated ORF, orf77, encode an RGSGR motif. Overexpression of all3290 and orf77 under the control of the petE promoter inhibited heterocyst formation, indicating that the RGSGR motif can inhibit heterocyst development in a variety of contexts.

Present address: Department of Veterinary Pathobiology, Texas A&M University, College Station, TX 77843.

Present address: 824 NW 52nd St., Seattle, WA 98127.

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