title: Arabidopsis AtHB7 and AtHB12 evolved divergently to fine tune processes associated with growth and responses to water stress.
abstract: BACKGROUND
  Arabidopsis AtHB7 and AtHB12 transcription factors (TFs) belong to the homeodomain-leucine zipper subfamily I (HD-Zip I) and present 62% amino acid identity. These TFs have been associated with the control of plant development and abiotic stress responses; however, at present it is not completely understood how AtHB7 and AtHB12 regulate these processes.
  
  
  RESULTS
  By using different expression analysis approaches, we found that AtHB12 is expressed at higher levels during early Arabidopsis thaliana development whereas AtHB7 during later developmental stages. Moreover, by analysing gene expression in single and double Arabidopsis mutants and in transgenic plants ectopically expressing these TFs, we discovered a complex mechanism dependent on the plant developmental stage and in which AtHB7 and AtHB12 affect the expression of each other. Phenotypic analysis of transgenic plants revealed that AtHB12 induces root elongation and leaf development in young plants under standard growth conditions, and seed production in water-stressed plants. In contrast, AtHB7 promotes leaf development, chlorophyll levels and photosynthesis and reduces stomatal conductance in mature plants. Moreover AtHB7 delays senescence processes in standard growth conditions.
  
  
  CONCLUSIONS
  We demonstrate that AtHB7 and AtHB12 have overlapping yet specific roles in several processes related to development and water stress responses. The analysis of mutant and transgenic plants indicated that the expression of AtHB7 and AtHB12 is regulated in a coordinated manner, depending on the plant developmental stage and the environmental conditions. The results suggested that AtHB7 and AtHB12 evolved divergently to fine tune processes associated with development and responses to mild water stress.
authors.forename: Delfina A
authors.initials: DA
authors.lastname: Ré
authors.forename: Matías
authors.initials: M
authors.lastname: Capella
authors.forename: Gustavo
authors.initials: G
authors.lastname: Bonaventure
authors.affiliation: Instituto de Agrobiotecnología del Litoral, Universidad Nacional del Litoral, CONICET, CC 242 Ciudad Universitaria, 3000 Santa Fe, Argentina. rchan@fbcb.unl.edu.ar.
authors.forename: Raquel L
authors.initials: RL
authors.lastname: Chan
mesh_terms: D017360:Arabidopsis / Q000254:growth & development* / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D003681:Dehydration; D019143:Evolution, Molecular; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D020131:Genes, Duplicate; D005966:Glucuronidase / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D010788:Photosynthesis / Q000235:genetics; D063245:Plant Development / Q000235:genetics*; D018515:Plant Leaves / Q000235:genetics / Q000254:growth & development; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development; D054046:Plant Stomata / Q000502:physiology; D011401:Promoter Regions, Genetic / Q000235:genetics; D036226:Seedlings / Q000235:genetics / Q000254:growth & development; D012639:Seeds / Q000378:metabolism; D016415:Sequence Alignment; D013312:Stress, Physiological / Q000235:genetics; D014867:Water / Q000378:metabolism
chemical_list: C494974:ATHB7 protein, Arabidopsis; D029681:Arabidopsis Proteins; C000594519:AtHB12 protein, Arabidopsis; D018398:Homeodomain Proteins; D014867:Water; D002734:Chlorophyll; D005966:Glucuronidase