title: An active Mitochondrial Complex II Present in Mature Seeds Contains an Embryo-Specific Iron-Sulfur Subunit Regulated by ABA and bZIP53 and Is Involved in Germination and Seedling Establishment.
abstract: Complex II (succinate dehydrogenase) is an essential mitochondrial enzyme involved in both the tricarboxylic acid cycle and the respiratory chain. InArabidopsis thaliana, its iron-sulfur subunit (SDH2) is encoded by three genes, one of them (SDH2.3) being specifically expressed during seed maturation in the embryo. Here we show that seedSDH2.3expression is regulated by abscisic acid (ABA) and we define the promoter region (-114 to +49) possessing all thecis-elements necessary and sufficient for high expression in seeds. This region includes between -114 and -32 three ABRE (ABA-responsive) elements and one RY-enhancer like element, and we demonstrate that these elements, although necessary, are not sufficient for seed expression, our results supporting a role for the region encoding the 5' untranslated region (+1 to +49). TheSDH2.3promoter is activated in leaf protoplasts by heterodimers between the basic leucine zipper transcription factors bZIP53 (group S1) and bZIP10 (group C) acting through the ABRE elements, and by the B3 domain transcription factor ABA insensitive 3 (ABI3). Thein vivorole of bZIP53 is further supported by decreasedSDH2.3expression in a knockdownbzip53mutant. By using the protein synthesis inhibitor cycloheximide andsdh2mutants we have been able to conclusively show that complex II is already present in mature embryos before imbibition, and contains mainly SDH2.3 as iron-sulfur subunit. This complex plays a role during seed germinationsensu-strictosince we have previously shown that seeds lacking SDH2.3 show retarded germination and now we demonstrate that low concentrations of thenoyltrifluoroacetone, a complex II inhibitor, also delay germination. Furthermore, complex II inhibitors completely block hypocotyl elongation in the dark and seedling establishment in the light, highlighting an essential role of complex II in the acquisition of photosynthetic competence and the transition from heterotrophy to autotrophy.
authors.affiliation: Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile Santiago, Chile.
authors.forename: Franko
authors.initials: F
authors.lastname: Restovic
authors.affiliation: Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile Santiago, Chile.
authors.forename: Roberto
authors.initials: R
authors.lastname: Espinoza-Corral
authors.affiliation: Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile Santiago, Chile.
authors.forename: Isabel
authors.initials: I
authors.lastname: Gómez
authors.affiliation: Centro de Biotecnología y Genómica de Plantas - UPM-INIA, Campus de Montegancedo, Universidad Politécnica de Madrid Madrid, Spain.
authors.forename: Jesús
authors.initials: J
authors.lastname: Vicente-Carbajosa
authors.affiliation: Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile Santiago, Chile.
authors.forename: Xavier
authors.initials: X
authors.lastname: Jordana
keywords: ABI3; Arabidopsis seed germination; abscisic acid; bZIPs; iron–sulfur subunit; mitochondrial respiratory complex; seedling establishment; succinate dehydrogenase