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Wang, Yan; Lyu, Wenhui; Berkowitz, Oliver; Radomiljac, Jordan D.; Law, Simon R.; Murcha, Monika W.; Carrie, Chris; Teixeira, Pedro F.; Kmiec, Beata; Duncan, Owen; Aken, Olivier van; Narsai, Reena; Glaser, Elzbieta; Huang, Shaobai; Roessner, Ute; Millar, A. Harvey; Whelan, James (2016): Inactivation of Mitochondrial Complex I Induces the Expression of a Twin Cysteine Protein that Targets and Affects Cytosolic, Chloroplastidic and Mitochondrial Function. In: Molecular Plant, Vol. 9, No. 5: pp. 696-710
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Abstract

At12Cys-1 (At5g64400) and At12Cys-2 (At5g09570) are two closely related isogenes that encode small, twin cysteine proteins, typically located in mitochondria. At12Cys-2 transcript is induced in a variety of mutants with disrupted mitochondrial proteins, but an increase in At12Cys protein is only detected in mutants with reduced mitochondrial complex I abundance. Induction of At12Cys protein in mutants that lack mitochondrial complex I is accompanied by At12Cys protein located in mitochondria, chloroplasts, and the cytosol. Biochemical analyses revealed that even single gene deletions, i.e., At12cys-1 or At12cys-2, have an effect on mitochondrial and chloroplast functions. However, only double mutants, i.e., At12cys-1: At12cys-2, affect the abundance of protein and mRNA transcripts encoding translation elongation factors as well as rRNA abundance. Blue native PAGE showed that At12Cys co-migrated with mitochondrial supercomplex I + III. Likewise, deletion of both At12cys-1 and At12cys-2 genes, but not single gene deletions, results in enhanced tolerance to drought and light stress and increased anti-oxidant capacity. The induction and multiple localization of At12Cys upon a reduction in complex I abundance provides a mechanism to specifically signal mitochondrial dysfunction to the cytosol and then beyond to other organelles in the cell.