title: A tree ortholog of APETALA1 mediates photoperiodic control of seasonal growth.
abstract: BACKGROUND
  Photoperiodic control of development plays a key role in adaptation of plants to seasonal changes. A signaling module consisting of CONSTANS (CO) and FLOWERING LOCUS T (FT) mediates in photoperiodic control of a variety of developmental transitions (e.g., flowering, tuberization, and seasonal growth cessation in trees). How this conserved CO/FT module can mediate in the photoperiodic control of diverse unrelated developmental programs is poorly understood.
  
  
  RESULTS
  We show that Like-AP1 (LAP1), a tree ortholog of Arabidopsis floral meristem identity gene APETALA1 (AP1), mediates in photoperiodic control of seasonal growth cessation downstream of the CO/FT module in hybrid aspen. Using LAP1 overexpressors and RNAi-suppressed transgenic trees, we demonstrate that short day (SD)-mediated downregulation of LAP1 expression is required for growth cessation. In contrast with AP1 targets in flowering, LAP1 acts on AINTEGUMENTA-like 1 transcription factor, which is implicated in SD-mediated growth cessation. Intriguingly, unlike AP1 in Arabidopsis, ectopic expression of LAP1 fails to induce early flowering in hybrid aspen trees.
  
  
  CONCLUSIONS
  These results indicate that AP1 ortholog in trees has acquired a novel function in photoperiodic regulation of seasonal growth. Thus, photoperiodic signaling pathway may have diverged downstream of AP1/LAP1 rather than the CO/FT module during evolution. Moreover, control of flowering by the CO/FT module can be uncoupled from its role in photoperiodic control of seasonal growth in trees. Thus, our findings can explain mechanistically how a conserved signaling module can mediate in the control of a highly diverse set of developmental transitions by a similar input signal, namely photoperiod.
authors.affiliation: Umeå Plant Science Center, Department of Forest Genetics and Plant Physiology, SLU, 90187 Umeå, Sweden.
authors.forename: Abdul
authors.initials: A
authors.lastname: Azeez
authors.affiliation: Umeå Plant Science Center, Department of Forest Genetics and Plant Physiology, SLU, 90187 Umeå, Sweden.
authors.forename: Pál
authors.initials: P
authors.lastname: Miskolczi
authors.affiliation: Umeå Plant Science Center, Department of Forest Genetics and Plant Physiology, SLU, 90187 Umeå, Sweden.
authors.forename: Szymon
authors.initials: S
authors.lastname: Tylewicz
authors.affiliation: Umeå Plant Science Center, Department of Forest Genetics and Plant Physiology, SLU, 90187 Umeå, Sweden. Electronic address: rishi.bhalerao@slu.se.
authors.forename: Rishikesh P
authors.initials: RP
authors.lastname: Bhalerao
mesh_terms: D029681:Arabidopsis Proteins / Q000737:chemistry; D018506:Gene Expression Regulation, Plant; D023281:Genomics; D026161:MADS Domain Proteins / Q000737:chemistry; D017440:Photoperiod; D010802:Phylogeny; D063245:Plant Development / Q000235:genetics*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D030821:Plants, Genetically Modified / Q000254:growth & development; D032107:Populus / Q000235:genetics* / Q000254:growth & development; D012621:Seasons; D016415:Sequence Alignment
chemical_list: C091535:AP1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D026161:MADS Domain Proteins; D010940:Plant Proteins