Redox Regulation of LSD1/CATALASE 2 Phase Separation Condensates Controls Location and Functions.

Phase separation of proteins into membraneless compartments is emerging as an important mechanism of plant developmental and stress responses. We show Arabidopsis catalase 2 (CAT2) is recruited to phase-separated condensates with LESION SIMULATING DISEASE1 (LSD1), a plant-specific regulator of programmed cell death, in a redox-dependent manner that regulates its intracellular localisation and activity. Using recombinant proteins, we showed that CAT2 and LSD1 form ternary complexes with the peroxisome import receptor PEX5. The ability of LSD1 to form phase-separated condensates is a property of zinc fingers 1 and 2. The interactions between all three proteins and the fluidity of the LSD1 condensates are redox-regulated. Using confocal microscopy, the in vivo trafficking of CAT2 to peroxisomes and the nuclei was shown to be redox-regulated, and LSD1 was shown to control CAT2 localisation in vivo. We propose a model whereby the redox-dependent differential accessibility of CAT2, PEX5 and LSD1 within condensates not only regulates CAT2 activity but also compartmentalisation between peroxisome, cytosol and nucleus. Relocation of catalase to the nucleus may provide protection to nuclear processes under conditions of biotic stress.