Investigation of singlet‐oxygen‐responsive genes in the cyanobacterium SynechocystisPCC 6803

Abstract

AbstractSinglet 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‐responsive 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 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 sigD, some components of the transcriptomes induced by salt‐, hyperosmotic and cold‐stress, as well as several genes of unknown function. The most pronounced 1O2‐induced upregulation was observed for the hliB and the co‐transcribed lilA genes, whose deletion induced enhanced sensitivity 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.