ABSTRACT
Abiotic stress on living cells can be dened as environmental conditions capable of causing potentially injurious effects. Clearly if the magnitude and duration of the change in environmental factor is suf- cient, then a certain degree of stress is perceived by the organism. Living organisms may not be able to acclimatize upon sudden exposure to severe stress thus leading to their death. But, they can acclimatize to gradual changes in environmental conditions by sensing them, followed by induction and/or optimization of various biochemical and cellular processes. Therefore, survival under abiotic stress depends primarily on the organism’s ability to “sense” the change in the environment and transduce the signal to target genes in the genome, ultimately bringing about altered expression of genes. Thus, upon sensing the changes in environmental conditions, the proteins that are synthesized (stress-specic proteins) are involved in acclimation of the organism to the changed environment (Figure 7.1). Cyanobacteria use a
7.1 Introduction .......................................................................................................................... 155 7.1.1 Molecular Adaptation to Extreme Temperatures ..................................................... 156 7.1.2 Synechocystis as a Model to Study Cold Acclimation ............................................. 157 7.1.3 Responses to Low-Temperature at the Transcriptional Level .................................. 157
7.2 Low-Temperature-Inducible Proteins and Mechanisms of Cold Acclimation ..................... 161 7.2.1 Desaturases and Membrane Fluidity Optimization .................................................. 161 7.2.2 Cold-Inducible RNA Helicases ................................................................................. 162 7.2.3 Cold-Inducible RNA Binding Proteins ..................................................................... 162 7.2.4 Ribosomal Proteins and Translation ......................................................................... 162 7.2.5 Folding and Quality Control of Proteins during Cold Acclimation ......................... 163 7.2.6 Other Low-Temperature-Inducible Genes ................................................................ 163
7.3 Low-Temperature Sensing and Signal Transduction ............................................................ 163 7.3.1 Membrane Fluidity as a Low-Temperature Signal ................................................... 163 7.3.2 Two-Component Systems for Low-Temperature Signal Perception ......................... 164 7.3.3 Low-Temperature Sensing through Changes in DNA Supercoiling......................... 164 7.3.4 Low-Temperature Sensing through Changes in RNA Conformation ....................... 165
7.4 Conclusions ........................................................................................................................... 165 Acknowledgments .......................................................................................................................... 166 References ...................................................................................................................................... 166
two-component signal transduction system, involving a sensory kinase and a response regulator, as a means to perceive stress signal and to transduce the signal to the target genes for regulated expression. In addition different transcription factors and alternative sigma factors are proposed to be involved in regulation of stress-inducible gene expression (Figure 7.1).
