title: Functioning haemoglobin genes in non-nodulating plants.
abstract: Haemoglobin has previously been recorded in plants only in the nitrogen-fixing nodules formed by symbiotic association between Rhizobium or Frankia and legume or non-legume hosts. Structural similarities amongst these and animal haemoglobins at the protein and gene level suggested a common evolutionary origin. This suggests that haemoglobin genes, inherited from an ancestor common to plants and animals, might be present in all plants. We report here the isolation of a haemoglobin gene from Trema tomentosa, a non-nodulating relative of Parasponia (Ulmaceae). The gene has three introns located at positions identical to those in the haemoglobin genes of nodulating plant species, strengthening the case for a common origin of all plant haemoglobin genes. The data argue strongly against horizontal haemoglobin gene transfer from animals to plants. The Trema gene has a tissue-specific pattern of transcription and translation, producing monomeric haemoglobin in Trema roots. We have also found that the Parasponia haemoglobin gene is transcribed in roots of non-nodulated plants. These results suggest that haemoglobin has a role in the respiratory metabolism of root cells of all plant species. We propose that its special role in nitrogen-fixing nodules has required adaptation of the haemoglobin-gene regulation pathway, to give high expression in the specialized environment of the nodule.
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D004247:DNA / Q000235:genetics; D006454:Hemoglobins / Q000235:genetics*; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D010940:Plant Proteins / Q000032:analysis / Q000235:genetics; D010944:Plants / Q000235:genetics*; D012313:RNA / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D014158:Transcription, Genetic
chemical_list: D006454:Hemoglobins; D010940:Plant Proteins; D012333:RNA, Messenger; D012313:RNA; D004247:DNA