title: The origin and evolution of plant cystatins and their target cysteine proteinases indicate a complex functional relationship.
abstract: BACKGROUND
  Cystatins and their putative targets, the families of cysteine proteinases C1A and C13 play key roles in plants. Comparative genomic analyses are powerful tools to obtain valuable insights into the conservation and evolution of the proteinases and their proteinaceous inhibitors, and could aid to elucidate issues concerning the function of these proteins.
  
  
  RESULTS
  We have performed an evolutionary comparative analysis of cysteine proteinases C1A and C13 and their putative inhibitors in representative species of different taxonomic groups that appeared during the evolution of the Viridiplantae. The results indicate that whereas C1A cysteine proteinases are present in all taxonomic groups, cystatins and C13 cysteine proteinases are absent in some basal groups. Moreover, gene duplication events have been associated to the increasing structural and functional complexities acquired in land plants.
  
  
  CONCLUSIONS
  Comparative genomic analyses have provided us valuable insights into the conservation and evolution of the cystatin inhibitory family and their putative targets, the cysteine proteinases from families C1A and C13. Functionality of both families of proteins in plants must be the result of a coevolutionary process that might have occurred during the evolution of basal and land plants leading to a complex functional relationship among them.
authors.affiliation: Laboratorio de Bioquímica y Biología Molecular, Dpto, de Biotecnología-Centro de Biotecnología y Genómica de Plantas-Universidad Politécnica de Madrid, ETS Ingenieros Agrónomos, Ciudad Universitaria s/n. 28040 Madrid, Spain. m.martinez@upm.es
authors.forename: Manuel
authors.initials: M
authors.lastname: Martinez
authors.forename: Isabel
authors.initials: I
authors.lastname: Diaz
mesh_terms: D015891:Cystatins / Q000235:genetics*; D003546:Cysteine Endopeptidases / Q000235:genetics*; D019143:Evolution, Molecular; D010802:Phylogeny; D010944:Plants / Q000235:genetics*
chemical_list: D015891:Cystatins; D003546:Cysteine Endopeptidases