A novel pathway for destructive singlet oxygen generation during osmotic stress in Arabidopsis roots

The climate crisis necessitates that we expand our knowledge of plants’ response to the changing environment in particular osmotic stress brought upon by drought. Singlet oxygen is an ephemeral reactive oxygen species with destructive oxidative properties. It was first noted in high-light photodynamic processes in photosynthesis. However recently, singlet oxygen was detected in roots during osmotic stress independent of light as a byproduct of enzymatic activity of the lipoxygenase (LOX) family. In Arabidopsis, LOX family members are divided into two enzymatic types; 9-LOX and 13-LOX. Both types use fatty acids for substrates but differ in their enzymatic products. We use the fluorescent reporter of singlet oxygen (SOSG), LOX-RFP labeled transgenic lines, organelle markers and lipidomics, to describe how singlet oxygen is generated in the cellular context during osmotic stress. We show novel singlet oxygen “bodies” that originate in the root plastid in addition to stress-induced accumulation of lipid droplets that originate at the ER. Furthermore, the role of plastid lipases that generate fatty acids from membranes during osmotic stress was identified. This work draws for the first time a unique molecular pathway to singlet oxygen production that ultimately leads to cell death and drought-induced tissue damage.