Cyanobacteria Signal Transduction System Validation, Comparative Genomics Analysis And Gene Function

During the long evolutionary history, cyanobacteria have developed a variety of response mechanisms to sense external or internal factors and to cope with the changing environmental conditions. The signal transduction system of cyanobacteria is constituted of two-component signal transduction system and eukaryotic-type serine/threonine kinases. Functional study was now mainly on one signal transduction system and in one cyanobacteria strain. In this study, comparative genomic analysis of the main cyanobacterial signal transduction systems has been employed. And then functions of some important genes have been examined.The number of genes in cyanobacterial signal transduction systems was the result of the genome size, ecophysiology, and physiological properties of the organisms. Similar conserved motifs and amino acids indicate that cyanobacterial STKs make use of a similar catalytic mechanism as eukaryotic STKs. Gain-and-loss is significant during the evolution of genes in cyanobacterial signal transduction systems, along with domain shuffling and insertion. Histidine kinases and response regulators in two-component signal transduction system may have different evolutionary history. This study has established an overall framework of sequence-structure-function interactions for the family of siganal transduction genes, which will be useful for the functional analysis.Synechococcus PCC7942 and Synechocystis PCC6803 are unicellular cyanobacteria in freshwater, which can be transformed naturally and is the model speices of molecular genetics of cyanobacteria. Funtion of two orthologous genes, synpcc7942₀095 and rre28, in Synechococcus and Synechocystis separately have been analyzed. We found that these two highly conserved orthologous genes have different functions. And the same histidine kinase could be activated different response regulators in different cyanobacteria strains. This phenomenon may be explained by the functional differentiation during the long evolutional history.Studies on serine/threonine kinases in cyanobacteria were limited. We have found that the serine/threonine kinase of SpkG in Synechocystis PCC6803was indicated to be involved in adaptation to high salt stress by mutant and RT-PCR analysis. We analyzed global gene expression in both the SpkG mutant and wild strain under normal and high salt conditions. Sixty genes have been found expressed differently in wild strain and SpkG mutant, which were mainly consisted of transport, energy metabolism, protein processing, envelope biogenesis and signal transduction. It is for the first time to confirm a serine/threonine kinase and two-component signal transduction system together constituting a complex network under high salt condiotion.Cyanobacteria have the characters of both bacteria and plant. The evolutional and ecologic dominance has made cyanobacteria important for the study of signal transduction systems. The availability of multiple sequenced genomes has been very helpful in phylogenetic and functional studies of cyanobacterial genes. And the study of signal transduction systems in cyanobacteria may provide important clues for the stress study of plants.