The Response Of Serine/threonine Protein Kinase SpkC Aganist High Temperature Stress In Synechocystis Sp.PCC 6803

Cyanobacteria have a wide range of habitats and even survive in a variety of extreme environments,indicating that cyanobacteria have evolved adaptive mechanisms such as signal transduction to cope with the changeable environment during the long process of evolution.Serine/threonine protein kinases is an important signal transduction system in cyanobacteria,they are involved in the response of external stress signals with other signal transduction systems.However,there are little research about serine/threonine protein kinases has been done in cyanobacteria.The previous study suggests that the serine/threonine kinase SpkC may be involved in the response to high temperature stress,but there is a lack of research on whether SpkC responds to high temperature stress and its regulatory mechansim in high temperature stress.In this study,we studied the response of serine/threonine kinase SpkC under high temperature stress to provide clues to reveal the regulatory mechanism of SpkC.Firstly,the spkC gene knockout mutant(AspkC)was constructed by homologous recombination.Then wild type strains and mutants were used as materials to study their phenotypes under high temperature stress.Under high temperature stress,the growth rate of the mutant AspkC was significantly slower than that of the wild strain under high temperature stress and the contents of photosynthetic pigments(chlorophyll,carotenoid and phycobilin)in the mutants were also significantly different from those in the wild strains.The activity of photosynthetic system ? in AspkC decreased more rapidly after short-term high-temperature stress.What's more,the mutant strain could not recover even if it returned to normal growth conditions,and the degree of recovery of photosynthetic system ? activity was also lower than that of the wild strain.Those results sugguests us the deletion of spkC led to severe defect response to high-temperature stress in Synechocystis sp.PCC 6803,and SpkC may be a positive regulator in high temperature stress.Last,we compared the differential gene expression of wild-type and AspkC mutants of Synechocystis under high temperature stress by RNA-seq.There were 184 differentially expressed genes between wild stype strains and AspkC,of which 88 were up-regulated and 96 were down-regulated.The results of GO enrichment and KEGG enrichment showed that the differential genes involved in translation,chlorophyll synthesis,fatty acid metabolism,and energy metabolism,indicating that SpkC regulates these physiological processes under high temperature stress,which were also consistent with phenotypes.After further analysis of these differentially expressed genes,we found that SpkC regulates eight heat-inducible genes,which proves us that it participates in the response to high temperature stress from the transcriptional level.We also focused on changes of signal transduction-related genes.After knock down of the spkC gene,the transcription levels of the RNA polymerases ?factor-sigH and sigG were up-regulated,and the expression of sigE was down-regulated.The expression of histidine kinase-encoding gene hikl6 was up-regulated,the gene encoding the response regulator slr6040,rre41,and rre34 was down-regulated.Those results show that SigH,SigG,SigE,Slr6040,Rre41,and Rre34 may be downstream components of SpkC in signal transduction,and there is cooperation between Hik16 and SpkC in response to high temperature stress.