Mitochondrial proteotoxic stresses activate abscisic acid signaling in plants

The mitochondrial proteome is composed of both mitochondrial DNA (mtDNA)-encoded and nuclear DNA (nuDNA)-encoded proteins. The mitonuclear protein imbalance leads to the occurrence of mitochondrial proteotoxic stresses. As a response to the mitochondrial proteotoxic stress, mitochondrial unfolded protein response (UPR mt ) is induced in cells to restore the mitochondrial functions. Although UPR mt has been extensively studied in animals, much less is known about the mechanisms of UPR mt signaling in plants. We report here that a DNA intercalating agent, ethidium bromide (EtBr) triggers UPR mt in Arabidopsis thaliana, with characteristic features similar to those caused by the mitochondrial translation inhibitor doxycycline (Dox). EtBr/Dox treatments activate abscisic acid (ABA) signaling. Then ABA promotes the expression of UPR mt genes, like alternative oxidase 1a ( AOX1a ). A key regulator of ABA signaling, ABA insensitive 5 (ABI5) directly binds to the promoter of AOX1a , which enhances AOX1a gene transcription. Our study reveals a link between ABA and UPR mt in plants. • Plant mitochondrial proteotoxic stresses activate abscisic acid (ABA) signaling; • A key regulator of ABA signaling, ABA insensitive 5 (ABI5) directly binds to the promoter of the mitochondrial unfolded protein response (UPR mt ) gene alternative oxidase 1a ( AOX1a ), and enhances AOX1a promoter activity; • Both ABA biosynthesis and ABA signaling are partially required for induction of UPR mt genes by ethidium bromide (EtBr)/doxycycline (Dox) treatments.