title: Reactive oxygen species and transcript analysis upon excess light treatment in wild-type Arabidopsis thaliana vs a photosensitive mutant lacking zeaxanthin and lutein.
abstract: BACKGROUND
  Reactive oxygen species (ROS) are unavoidable by-products of oxygenic photosynthesis, causing progressive oxidative damage and ultimately cell death. Despite their destructive activity they are also signalling molecules, priming the acclimatory response to stress stimuli.
  
  
  RESULTS
  To investigate this role further, we exposed wild type Arabidopsis thaliana plants and the double mutant npq1lut2 to excess light. The mutant does not produce the xanthophylls lutein and zeaxanthin, whose key roles include ROS scavenging and prevention of ROS synthesis. Biochemical analysis revealed that singlet oxygen (1O2) accumulated to higher levels in the mutant while other ROS were unaffected, allowing to define the transcriptomic signature of the acclimatory response mediated by 1O2 which is enhanced by the lack of these xanthophylls species. The group of genes differentially regulated in npq1lut2 is enriched in sequences encoding chloroplast proteins involved in cell protection against the damaging effect of ROS. Among the early fine-tuned components, are proteins involved in tetrapyrrole biosynthesis, chlorophyll catabolism, protein import, folding and turnover, synthesis and membrane insertion of photosynthetic subunits. Up to now, the flu mutant was the only biological system adopted to define the regulation of gene expression by 1O2. In this work, we propose the use of mutants accumulating 1O2 by mechanisms different from those activated in flu to better identify ROS signalling.
  
  
  CONCLUSIONS
  We propose that the lack of zeaxanthin and lutein leads to 1O2 accumulation and this represents a signalling pathway in the early stages of stress acclimation, beside the response to ADP/ATP ratio and to the redox state of both plastoquinone pool. Chloroplasts respond to 1O2 accumulation by undergoing a significant change in composition and function towards a fast acclimatory response. The physiological implications of this signalling specificity are discussed.
authors.affiliation: Dipartimento di Biotecnologie, Università di Verona, Strada Le Grazie 15, Verona, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Alboresi
authors.forename: Luca
authors.initials: L
authors.lastname: Dall'osto
authors.forename: Alessio
authors.initials: A
authors.lastname: Aprile
authors.forename: Petronia
authors.initials: P
authors.lastname: Carillo
authors.forename: Enrica
authors.initials: E
authors.lastname: Roncaglia
authors.forename: Luigi
authors.initials: L
authors.lastname: Cattivelli
authors.forename: Roberto
authors.initials: R
authors.lastname: Bassi
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D008027:Light; D014975:Lutein / Q000172:deficiency*; D009154:Mutation; D010788:Photosynthesis / Q000528:radiation effects; D017382:Reactive Oxygen Species / Q000378:metabolism*; D014158:Transcription, Genetic / Q000528:radiation effects*; D024341:Xanthophylls / Q000172:deficiency*; D065146:Zeaxanthins
chemical_list: D029681:Arabidopsis Proteins; D017382:Reactive Oxygen Species; D024341:Xanthophylls; D065146:Zeaxanthins; D014975:Lutein