The 30th International Conference on Arabidopsis Research (ICAR 2019)

538 / 2019-03-12 05:32:12

Control of Retrograde Signaling by Protein Import and Cytosolic Folding Stress

chloroplast, plastid-nuclear interaction, protein import, proteostasis

Plenary track > Cell Biology

Communication between organelles and the nucleus is essential for fitness and survival. Retrograde signals are cues emitted from the organelles to regulate nuclear gene expression. GENOMES UNCOUPLED1 (GUN1), a protein of unknown function, has emerged as a central integrator, participating in multiple retrograde signaling pathways that collectively regulate the nuclear transcriptome. Here we show that GUN1 regulates chloroplast protein import through interaction with the import-related chaperone cpHSC70-1. We demonstrated that overaccumulation of unimported precursor proteins (preproteins) in the cytosol causes a GUN phenotype in the wild type and enhances the GUN phenotype of the gun1 mutant. Furthermore, we identified the cytosolic HSP90 chaperone complex, induced by over-accumulated preproteins, as a central regulator of photosynthetic gene expression that determines the expression of the GUN phenotype. Taken together, our results suggest a model in which protein import capacity, folding stress and the cytosolic HSP90 complex control retrograde communication.