Singlet-Oxygen-Mediated Regulation of Photosynthesis-Specific Genes: A Role for Reactive Electrophiles in Signal Transduction.

During photosynthesis, reactive oxygen species (ROS) are formed, including hydrogen peroxide (HO) and singlet oxygen (O), which have putative roles in signalling, but their involvement in photosynthetic acclimation is unclear. Due to extreme reactivity and a short lifetime, O signalling occurs via its reaction products, such as oxidised poly-unsaturated fatty acids in thylakoid membranes. The resulting lipid peroxides decay to various aldehydes and reactive electrophile species (RES). Here, we investigated the role of ROS in the signal transduction of high light (HL), focusing on GreenCut2 genes unique to photosynthetic organisms. Using RNA seq. data, the transcriptional responses of to 2 h HL were compared with responses under low light to exogenous RES (acrolein; 4-hydroxynonenal), β-cyclocitral, a β-carotene oxidation product, as well as Rose Bengal, a O-producing photosensitiser, and HO. HL induced significant ( < 0.05) up- and down-regulation of 108 and 23 GreenCut2 genes, respectively. Of all HL up-regulated genes, over half were also up-regulated by RES, including (ribulose bisphosphate carboxylase small subunit), NPQ-related and . Furthermore, 96% of the genes down-regulated by HL were also down-regulated by O or RES, including (chlorophyllide- oxygnease), (NADP-malate dehydrogenase) and (phosphoglycerate mutase) for glycolysis. In comparison, only 0-4% of HL-affected GreenCut2 genes were similarly affected by HO or β-cyclocitral. Overall, O plays a significant role in signalling during the initial acclimation of to HL by up-regulating photo-protection and carbon assimilation and down-regulating specific primary metabolic pathways. Our data support that this pathway involves RES.