title: Integration of stress-related and reactive oxygen species-mediated signals by Topoisomerase VI in Arabidopsis thaliana.
abstract: Environmental stress often leads to an increased production of reactive oxygen species that are involved in plastid-to-nucleus retrograde signaling. Soon after the release of singlet oxygen ((1)O(2)) in chloroplasts of the flu mutant of Arabidopsis, reprogramming of nuclear gene expression reveals a rapid transfer of signals from the plastid to the nucleus. We have identified extraplastidic signaling constituents involved in (1)O(2)-initiated plastid-to-nucleus signaling and nuclear gene activation after mutagenizing a flu line expressing the luciferase reporter gene under the control of the promoter of a (1)O(2)-responsive AAA-ATPase gene (At3g28580) and isolating second-site mutations that lead to a constitutive up-regulation of the reporter gene or abrogate its (1)O(2)-dependent up-regulation. One of these mutants, caa39, turned out to be a weak mutant allele of the Topoisomerase VI (Topo VI) A-subunit gene with a single amino acid substitution. Transcript profile analysis of flu and flu caa39 mutants revealed that Topo VI is necessary for the full activation of AAA-ATPase and a set of (1)O(2)-responsive transcripts in response to (1)O(2). Topo VI binds to the promoter of the AAA-ATPase and other (1)O(2)-responsive genes, and hence could directly regulate their expression. Under photoinhibitory stress conditions, which enhance the production of (1)O(2) and H(2)O(2), Topo VI regulates (1)O(2)-responsive and H(2)O(2)-responsive genes in a distinct manner. These results suggest that Topo VI acts as an integrator of multiple signals generated by reactive oxygen species formed in plants under adverse environmental conditions.
authors.affiliation: Department of Biology, Zurich-Basel Plant Science Center,  Eidgenössiche Technische Hochschule Zurich, CH-8092 Zurich,  Switzerland.
authors.forename: Klára
authors.initials: K
authors.lastname: Simková
authors.forename: Fanny
authors.initials: F
authors.lastname: Moreau
authors.forename: Piotr
authors.initials: P
authors.lastname: Pawlak
authors.forename: Cécile
authors.initials: C
authors.lastname: Vriet
authors.forename: Aiswarya
authors.initials: A
authors.lastname: Baruah
authors.forename: Cristina
authors.initials: C
authors.lastname: Alexandre
authors.forename: Lars
authors.initials: L
authors.lastname: Hennig
authors.forename: Klaus
authors.initials: K
authors.lastname: Apel
authors.forename: Christophe
authors.initials: C
authors.lastname: Laloi
mesh_terms: D017360:Arabidopsis / Q000201:enzymology*; D029681:Arabidopsis Proteins / Q000235:genetics; D019843:Archaeal Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D047369:Chromatin Immunoprecipitation; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology*; D008156:Luciferases; D046228:Microarray Analysis; D009154:Mutation / Q000235:genetics; D018087:Plastids / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology*; D026082:Singlet Oxygen / Q000378:metabolism; D013312:Stress, Physiological / Q000502:physiology*
chemical_list: D029681:Arabidopsis Proteins; D019843:Archaeal Proteins; C478633:FLU protein, Arabidopsis; D017382:Reactive Oxygen Species; D026082:Singlet Oxygen; D008156:Luciferases; C105141:DNA topoisomerase VI; D004250:DNA Topoisomerases, Type II