Investigation of singlet oxygen sensitive genes in the cyanobacteriumSynechocystisPCC 6803

Abstract

SummarySinglet oxygen (1O2) is an important reactive oxygen species whose formation by the type-II, light-dependent, photodynamic reaction is inevitable during photosynthetic processes. In the last decades, the recognition that1O2is not only a damaging agent, but can also affect gene expression and participates in signal transduction pathways has received increasing attention. However, contrary to several other taxa,1O2-specific genes have not been identified in the important cyanobacterial model organismSynechocystisPCC 6803. By using global transcript analysis we have identified a large set of1O2-responsiveSynechocystisgenes, whose transcript levels were either enhanced or repressed in the presence of1O2. Characteristic1O2responses were observed in several light-inducible genes ofSynechocystis, especially in thehli(orscp) family encoding HLIP/SCP proteins involved in photoprotection. Other important1O2-induced genes include components of the Photosystem II repair machinery (psbA2andftsH2,ftsH3), iron homeostasis genesisiAandidiA, the Group-2 sigma factorsigD, some components of the transcriptomes induced by salt-, hyperosmotic and cold-stress, as well as several genes of unknown function. One of the most pronounced1O2-induced upregulation was observed for thehliBgene, whose deletion provided tolerance against1O2-mediated light damage. A bioreporterSynechocystisstrain was created by fusing thehliBpromoter to the bacterial luciferase (lux), which showed its utility for continuous monitoring of1O2concentrations inside the cell.