title: Downregulation of leaf flavin content induces early flowering and photoperiod gene expression in Arabidopsis.
abstract: BACKGROUND
  Riboflavin is the precursor of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), essential cofactors for many metabolic enzymes that catalyze a variety of biochemical reactions. Previously we showed that free flavin (riboflavin, FMN, and FAD) concentrations were decreased in leaves of transgenic Arabidopsis plants expressing a turtle riboflavin-binding protein (RfBP). Here, we report that flavin downregulation by RfBP induces the early flowering phenotype and enhances expression of floral promoting photoperiod genes.
  
  
  RESULTS
  Early flowering was a serendipitous phenomenon and was prudently characterized as a constant phenotype of RfBP-expressing transgenic Arabidopsis plants in both long days and short days. The phenotype was eliminated when leaf free flavins were brought back to the steady-state levels either by the RfBP gene silencing and consequently nullified production of the RfBP protein, or by external riboflavin feeding treatment. RfBP-induced early flowering was correlated with enhanced expression of floral promoting photoperiod genes and the florigen gene FT in leaves but not related to genes assigned to vernalization, autonomous, and gibberellin pathways, which provide flowering regulation mechanisms alternative to the photoperiod. RfBP-induced early flowering was further correlated with increased expression of the FD gene encoding bZIP transcription factor FD essential for flowering time control and the floral meristem identity gene AP1 in the shoot apex. By contrast, the expression of FT and photoperiod genes in leaves and the expression of FD and AP1 in the shoot apex were no longer enhanced when the RfBP gene was silenced, RfBP protein production canceled, and flavin concentrations were elevated to the steady-state levels inside plant leaves.
  
  
  CONCLUSIONS
  Token together, our results provide circumstantial evidence that downregulation of leaf flavin content by RfBP induces early flowering and coincident enhancements of genes that promote flowering through the photoperiod pathway.
authors.forename: Hongtao
authors.initials: H
authors.lastname: Ji
authors.forename: Yueyue
authors.initials: Y
authors.lastname: Zhu
authors.forename: Shan
authors.initials: S
authors.lastname: Tian
authors.forename: Manyu
authors.initials: M
authors.lastname: Xu
authors.forename: Yimin
authors.initials: Y
authors.lastname: Tian
authors.forename: Liang
authors.initials: L
authors.lastname: Li
authors.forename: Huan
authors.initials: H
authors.lastname: Wang
authors.forename: Li
authors.initials: L
authors.lastname: Hu
authors.forename: Yu
authors.initials: Y
authors.lastname: Ji
authors.forename: Jun
authors.initials: J
authors.lastname: Ge
authors.forename: Weigang
authors.initials: W
authors.lastname: Wen
authors.affiliation: Plant Growth and Defense Signaling Laboratory, State Ministry of Education Key Laboratory of Integrated Management of Crop Pathogens and Insect Pests, Nanjing Agricultural University, Nanjing 210095, China. hsdong@njau.edu.cn.
authors.forename: Hansong
authors.initials: H
authors.lastname: Dong
mesh_terms: D000818:Animals; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D005486:Flavin Mononucleotide / Q000378:metabolism; D005182:Flavin-Adenine Dinucleotide / Q000378:metabolism; D005415:Flavins / Q000235:genetics* / Q000378:metabolism*; D035264:Flowers / Q000235:genetics* / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D017440:Photoperiod; D018515:Plant Leaves; D018520:Plant Shoots / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C503117:FD protein, Arabidopsis; D005415:Flavins; D026901:Membrane Transport Proteins; D014157:Transcription Factors; C019079:riboflavin-binding protein; D005182:Flavin-Adenine Dinucleotide; D005486:Flavin Mononucleotide