Poikilothermic organisms sense and adapt to changes in ambient temperature. The cyanobacteria Synechocystis sense changes in membrane fluidity as indicators of changes in temperature. Suzuki et al. performed systematic mutagenesis of Synechocystis to identify the components of the signal transduction pathway for responding to low temperature. Two histidine kinase genes, hik19 and hik33, were identified along with a third gene, rer1. Mutants of hik19 or hik33 showed decreased stimulation of low-temperature-induced genes, desB and desD, in response to low temperature. Mutation of the rer1 gene resulted only in a reduced response of the desB gene to low temperature. On the basis of the genetic interactions and the sequence analysis of the predicted proteins from these three genes, the authors propose a signal transduction mechanism whereby Hik33 is the cold sensor in the plasma membrane, Hik19 transduces the signal, and Rer1 is one of several targets that can regulate transcription of genes whose expression is altered in response to low temperature.
Suzuki, I., Los, D.A., Kanesaki, Y., Mikami, K., and Murata, N. (2000) The pathway for perception and transduction of low-temperature signals in Synechocystis. EMBO J. 19: 1327-1334. [Abstract] [Full Text]