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Published on July 30, 2008; 10.1104/pp.108.123505

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Received May 25, 2008
Accepted July 23, 2008

An AbrB-like transcriptional regulator, Sll0822, is essential for the activation of nitrogen-regulated genes in Synechocystis sp. PCC 6803

Ai Ishii and Yukako Hihara *

Department of Biochemistry and Molecular Biology, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan

* Corresponding author; email: hihara{at}molbiol.saitama-u.ac.jp.

Every cyanobacterial species possesses multiple genes encoding AbrB-like transcriptional regulators (cyAbrBs) distinct from those conserved among other bacterial species. In this study, two genes encoding cyAbrBs in Synechocystis sp. PCC 6803, sll0359 and sll0822, were insertionally disrupted in order to examine their physiological roles. A fully segregated disrupted-mutant of sll0822 ({Delta}sll0822 mutant) but not of sll0359 was obtained, although both mutants exhibited similar phenotypes, i.e., a decrease in growth rate and pigment content. The growth rate of the {Delta}sll0822 mutant was low under any condition, but the low pigment content could be partially recovered by nitrate supplementation of the medium. DNA microarray and RNA gel blot analyses revealed that the level of expression of a part of the NtcA regulon such as urtA, amt1, glnB, sigE, and the nrt operon was significantly decreased in the {Delta}sll0822 mutant, although the induction of these genes upon nitrogen depletion was still observed to some extent. Sll0822 seems to work in parallel with NtcA to achieve flexible regulation of the nitrogen uptake system. The Sll0822 protein exists mainly in a dimeric form in vivo, and the amount of the protein was not affected by nitrogen availability. This observation together with the low binding-specificity of the purified His-tagged Sll0822 protein implies that the activity of Sll0822 may be post-translationally modulated in Synechocystis cells.






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