Overexpression of farnesyl diphosphate synthase in Arabidopsis mitochondria triggers light-dependent lesion formation and alters cytokinin homeostasis David Manzano 1,4 , Antoni Busquets 1 , Marta Closa 1 , Kla´ra Hoyerova´ 2 , Hubert Schaller 3 , Miroslav Kamı´nek 2 , Montserrat Arro´ 1 and Albert Ferrer 1, * 1 Departament de Bioquı´mica i Biologia Molecular, Facultat de Farma `cia, Universitat de Barcelona, Avda. Diagonal 643, Barcelona 08028, Spain (*author for correspondence; e-mail albertferrer@ub.edu); 2 Institute of Experimental Botany, Academy of Sciences of the Czech Republic, Rozvojova 135, Prague 6 CZ-165 02, Czech Republic; 3 De´partement Isopre´noı¨des, Institut de Biologie Mole´culaire des Plantes (IBMP/CNRS), Institut de Botanique, 28, rue Goethe, Strasbourg 67083, France; 4 Department of Cell and Developmental Biology, John Innes Centre, Colney Lane, Norwich NR4 7UH, UK Received 20 September 2005; accepted in revised form 31 December 2005 Key words: Arabidopsis thaliana, cytokinin, farnesyl diphosphate synthase, isoprenoid, mevalonic acid, mitochondria Abstract To investigate the role of mitochondrial farnesyl diphosphate synthase (FPS) in plant isoprenoid biosynthesis we characterized transgenic Arabidopsis thaliana plants overexpressing FPS1L isoform. This overexpressed protein was properly targeted to mitochondria yielding a mature and active form of the enzyme of 40 kDa. Leaves from transgenic plants grown under continuous light exhibited symptoms of chlorosis and cell death correlating to H 2 O 2 accumulation, and leaves detached from the same plants displayed accelerated senes- cence. Overexpression of FPS in mitochondria also led to altered leaf cytokinin profile, with a reduction in the contents of physiologically active trans-zeatin- and isopentenyladenine-type cytokinins and their corre- sponding riboside monophosphates as well as enhanced levels of cis-zeatin 7-glucoside and storage cytokinin O-glucosides. Overexpression of 3-hydroxy-3-methylglutaryl coenzyme A reductase did not prevent chlorosis in plants overexpressing FPS1L, but did rescue accelerated senescence of detached leaves and restored wild- type levels of cytokinins. We propose that the overexpression of FPS1L leads to an enhanced uptake and metabolism of mevalonic acid-derived isopentenyl diphosphate and/or dimethylallyl diphosphate by mito- chondria, thereby altering cytokinin homeostasis and causing a mitochondrial dysfunction that renders plants more sensitive to the oxidative stress induced by continuous light. Abbreviations: AOX, alternative oxidase; CaMV, cauliflower mosaic virus; Cox, cytochrome oxidase; DAB, 3,3¢-diaminobenzidine; DMAPP, dimethylallyl diphosphate; ER, endoplasmic reticulum; FPP, farnesyl diphosphate; FPS, farnesyl diphosphate synthase; GFP, green fluorescent protein; HMGR, 3-hydroxy- 3-methylglutaryl coenzyme A reductase; IP, isopentenyladenine; iP7G, N 6 -(D 2 -isopentenyl)adenine 7- glucoside; iPR, N 6 -(D 2 -isopentenyl)adenosine; iPRMP, N 6 -(D 2 -isopentenyl)adenosine 5¢-monophosphate; IPP, isopentenyl diphosphate; IPT, isopentenyltransferase; MEP, methylerythritol phosphate; MVA, mevalonic acid; ROS, reactive oxygen species; c-Z, cis-zeatin; t-Z, trans-zeatin; c-Z7G, cis-zeatin 7-glucoside; t-Z7G, trans-zeatin 7-glucoside; t-Z9G, trans-zeatin 9-glucoside; t-ZOG, trans-zeatin O-glucoside; c-ZR, cis-zeatin riboside; t-ZR, trans-zeatin riboside; t-ZRMP, trans-zeatin riboside 5¢-monophosphate; t-ZROG, trans-zeatin 9-riboside O-glucoside Plant Molecular Biology (2006) 61:195–213 Ó Springer 2006 DOI 10.1007/s11103-006-6263-y