Investigation of singlet oxygen sensitive genes in the cyanobacterium Synechocystis PCC 6803

Singlet 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 that 1O2 is 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 organism Synechocystis PCC 6803. By using global transcript analysis we have identified a large set of 1O2-responsive Synechocystis genes, whose transcript levels were either enhanced or repressed in the presence of 1O2. Characteristic 1O2 responses were observed in several light-inducible genes of Synechocystis , especially in the hli (or scp ) family encoding HLIP/SCP proteins involved in photoprotection. Other important 1O2-induced genes include components of the Photosystem II repair machinery ( psbA2 and ftsH2 , ftsH3 ), iron homeostasis genes isiA and idiA , the Group-2 sigma factor sig D, some components of the transcriptomes induced by salt-, hyperosmotic and cold-stress, as well as several genes of unknown function. One of the most pronounced 1O2-induced upregulation was observed for the hliB gene, whose deletion provided tolerance against 1O2-mediated light damage. A bioreporter Synechocystis strain was created by fusing the hliB promoter to the bacterial luciferase (lux), which showed its utility for continuous monitoring of 1O2 concentrations inside the cell. ### Competing Interest Statement The authors have declared no competing interest. * Chl : Chlorophyll BChl : bacteriochlorophyll HL : high light HLIP : high-light-inducible protein LL : low light MB : Methylene blue 1O2 : Singlet oxygen PSII : Photosystem II qPCR : quantitative PCR RB : Rose Bengal SCP : Small chlorophyll binding protein