title: Seed-specific elevation of non-symbiotic hemoglobin AtHb1: beneficial effects and underlying molecular networks in Arabidopsis thaliana.
abstract: BACKGROUND
  Seed metabolism is dynamically adjusted to oxygen availability. Processes underlying this auto-regulatory mechanism control the metabolic efficiency under changing environmental conditions/stress and thus, are of relevance for biotechnology. Non-symbiotic hemoglobins have been shown to be involved in scavenging of nitric oxide (NO) molecules, which play a key role in oxygen sensing/balancing in plants and animals. Steady state levels of NO are suggested to act as an integrator of energy and carbon metabolism and subsequently, influence energy-demanding growth processes in plants.
  
  
  RESULTS
  We aimed to manipulate oxygen stress perception in Arabidopsis seeds by overexpression of the non-symbiotic hemoglobin AtHb1 under the control of the seed-specific LeB4 promoter. Seeds of transgenic AtHb1 plants did not accumulate NO under transient hypoxic stress treatment, showed higher respiratory activity and energy status compared to the wild type. Global transcript profiling of seeds/siliques from wild type and transgenic plants under transient hypoxic and standard conditions using Affymetrix ATH1 chips revealed a rearrangement of transcriptional networks by AtHb1 overexpression under non-stress conditions, which included the induction of transcripts related to ABA synthesis and signaling, receptor-like kinase- and MAP kinase-mediated signaling pathways, WRKY transcription factors and ROS metabolism. Overexpression of AtHb1 shifted seed metabolism to an energy-saving mode with the most prominent alterations occurring in cell wall metabolism. In combination with metabolite and physiological measurements, these data demonstrate that AtHb1 overexpression improves oxidative stress tolerance compared to the wild type where a strong transcriptional and metabolic reconfiguration was observed in the hypoxic response.
  
  
  CONCLUSIONS
  AtHb1 overexpression mediates a pre-adaptation to hypoxic stress. Under transient stress conditions transgenic seeds were able to keep low levels of endogenous NO and to maintain a high energy status, in contrast to wild type. Higher weight of mature transgenic seeds demonstrated the beneficial effects of seed-specific overexpression of AtHb1.
authors.affiliation: Leibniz-Institut für Pflanzengenetik und Kulturpflanzenforschung (IPK), Corrensstr, 3, 06466 Gatersleben, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Thiel
authors.forename: Hardy
authors.initials: H
authors.lastname: Rolletschek
authors.forename: Svetlana
authors.initials: S
authors.lastname: Friedel
authors.forename: John E
authors.initials: JE
authors.lastname: Lunn
authors.forename: Thuy H
authors.initials: TH
authors.lastname: Nguyen
authors.forename: Regina
authors.initials: R
authors.lastname: Feil
authors.forename: Henning
authors.initials: H
authors.lastname: Tschiersch
authors.forename: Martin
authors.initials: M
authors.lastname: Müller
authors.forename: Ljudmilla
authors.initials: L
authors.lastname: Borisjuk
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics*; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D053263:Gene Regulatory Networks; D006454:Hemoglobins / Q000235:genetics*; D009569:Nitric Oxide / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D018384:Oxidative Stress; D010100:Oxygen / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D018749:RNA, Plant / Q000235:genetics; D012639:Seeds / Q000235:genetics / Q000378:metabolism*; D013312:Stress, Physiological
chemical_list: C470347:AHB1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D006454:Hemoglobins; D018749:RNA, Plant; D009569:Nitric Oxide; D010100:Oxygen