Affiliation:
1. Department of Plant and Environmental Sciences, Hebrew University of Jerusalem, 91904 Jerusalem, Israel
2. Bioscience Center, Nagoya University, Nagoya, Japan
3. Department of Biochemistry and Molecular Biology, Saitama University, Saitama, Japan
4. National Institute for Basic Biology, Okazaki, Japan
Abstract
The reason(s) for glucose sensitivity in certain cyanobacterial strains is poorly understood. Inactivation of genes encoding the putative sensor kinase Hik31 inSynechocystissp. strain PCC 6803 resulted in a mutant unable to grow in the presence ofd-glucose. Sensitivities tod-glucose, its analogue 2-deoxy-d-glucose, and fructose, were alleviated in mutants in whichglcP, encoding the glucose transporter, was inactivated. These data indicate that permeation of these substrates is required to inflict cell death. The mutant Δhik31, and the glucose-sensitive strain ofSynechocystis, do not possess glucokinase activity, although a transcript originating fromglk, encoding glucokinase, is present. Inactivation ofglkled to severe sensitivity to glucose, indicating that the presence of glucose itself, within the cells, inflicted this sensitivity. On the other hand, sensitivity to 2-deoxy-d-glucose was lower in Δglk, thus distinguishing between the effect of glucose itself and that of its analogue, which, in the absence of glucokinase activity, may not be phosphorylated. Addition of glucose led to a small rise in glucose-6-phosphate dehydrogenase activity in the wild type, but constitutive activity was observed in the Δhik31mutant regardless of the presence of glucose. Microarray analyses showed only small changes in the abundance of global transcripts inSynechocystisfollowing glucose addition, but the transcription levels of several genes, includingicfG, but notglk, were strongly affected by inactivation ofhik31. The mechanism(s) whereby Hik31 is involved in glucose sensing and response is discussed.