title: Apple EIN3 BINDING F-box 1 inhibits the activity of three apple EIN3-like transcription factors.
abstract: OBJECTIVE
  Fruit ripening in Malus× domestica (apple) is controlled by ethylene. Work in model species has shown that following the detection of ethylene, the ETHYLENE INSENSITIVE 3 (EIN3) transcription factor is stabilized, leading to an increase in transcript accumulation of ethylene-responsive genes, such as POLYGALACTURONASE1 (PG1). In the absence of ethylene, the EIN3 BINDING F-box (EBF) proteins rapidly degrade EIN3 via the ubiquitination/SCF (Skp, Cullin, F-Box) proteasome pathway. In this study, we aim to identify and characterize the apple EBF genes, and test their activity against apple EIN3-like proteins (EILs).
  
  
  METHODS
  The apple genome sequence was mined for EBF-like genes. The expression of EBF-like genes was measured during fruit development. Using a transient assay in Nicotiana benthamiana leaves, the activity of three apple EILs was tested against the PG1 promoter, with and without ethylene and EBF1.
  
  
  RESULTS
  Four EBF-like genes in apple were identified and grouped into two sub-clades. Sub-clade I genes had constant expression over fruit development while sub-clade II genes increased in expression at ripening. EBF1 was shown to reduce the transactivation of the apple PG1 promoter by the EIL1, EIL2 and EIL3 transcription factors in the presence of ethylene.
  
  
  CONCLUSIONS
  The apple EBF1 gene identified here is likely to be a functionally conserved EBF orthologue, modulating EIL activity in apples. The activity of EBF1 suggests that it is not specific to a single EIL, instead acting as a global regulator of apple EIL transcription factors.
authors.affiliation: The New Zealand Institute of Plant and Food Research , Private Bag 92169, Auckland 1142 , New Zealand ; School of Biological Sciences, University of Auckland , Private Bag 92019, Auckland 1142 , New Zealand.
authors.forename: Emma J
authors.initials: EJ
authors.lastname: Tacken
authors.forename: Hilary S
authors.initials: HS
authors.lastname: Ireland
authors.forename: Yen-Yi
authors.initials: YY
authors.lastname: Wang
authors.forename: Jo
authors.initials: J
authors.lastname: Putterill
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Schaffer