title: A genomics approach to understanding the role of auxin in apple (Malus x domestica) fruit size control.
abstract: BACKGROUND
  Auxin is an important phytohormone for fleshy fruit development, having been shown to be involved in the initial signal for fertilisation, fruit size through the control of cell division and cell expansion, and ripening related events. There is considerable knowledge of auxin-related genes, mostly from work in model species. With the apple genome now available, it is possible to carry out genomics studies on auxin-related genes to identify genes that may play roles in specific stages of apple fruit development.
  
  
  RESULTS
  High amounts of auxin in the seed compared with the fruit cortex were observed in 'Royal Gala' apples, with amounts increasing through fruit development. Injection of exogenous auxin into developing apples at the start of cell expansion caused an increase in cell size. An expression analysis screen of auxin-related genes involved in auxin reception, homeostasis, and transcriptional regulation showed complex patterns of expression in each class of gene. Two mapping populations were phenotyped for fruit size over multiple seasons, and multiple quantitative trait loci (QTLs) were observed. One QTL mapped to a region containing an Auxin Response Factor (ARF106). This gene is expressed during cell division and cell expansion stages, consistent with a potential role in the control of fruit size.
  
  
  CONCLUSIONS
  The application of exogenous auxin to apples increased cell expansion, suggesting that endogenous auxin concentrations are at least one of the limiting factors controlling fruit size. The expression analysis of ARF106 linked to a strong QTL for fruit weight suggests that the auxin signal regulating fruit size could partially be modulated through the function of this gene. One class of gene (GH3) removes free auxin by conjugation to amino acids. The lower expression of these GH3 genes during rapid fruit expansion is consistent with the apple maximising auxin concentrations at this point.
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited (PFR), Private Bag 92169, Auckland 1142, New Zealand.
authors.forename: Fanny
authors.initials: F
authors.lastname: Devoghalaere
authors.forename: Thomas
authors.initials: T
authors.lastname: Doucen
authors.forename: Baptiste
authors.initials: B
authors.lastname: Guitton
authors.forename: Jeannette
authors.initials: J
authors.lastname: Keeling
authors.forename: Wendy
authors.initials: W
authors.lastname: Payne
authors.forename: Toby John
authors.initials: TJ
authors.lastname: Ling
authors.forename: John James
authors.initials: JJ
authors.lastname: Ross
authors.forename: Ian Charles
authors.initials: IC
authors.lastname: Hallett
authors.forename: Kularajathevan
authors.initials: K
authors.lastname: Gunaseelan
authors.forename: G A
authors.initials: GA
authors.lastname: Dayatilake
authors.forename: Robert
authors.initials: R
authors.lastname: Diak
authors.forename: Ken C
authors.initials: KC
authors.lastname: Breen
authors.forename: D Stuart
authors.initials: DS
authors.lastname: Tustin
authors.forename: Evelyne
authors.initials: E
authors.lastname: Costes
authors.forename: David
authors.initials: D
authors.lastname: Chagné
authors.forename: Robert James
authors.initials: RJ
authors.lastname: Schaffer
authors.forename: Karine Myriam
authors.initials: KM
authors.lastname: David
mesh_terms: D002874:Chromosome Mapping; D005638:Fruit / Q000254:growth & development*; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D018745:Genome, Plant; D023281:Genomics; D007210:Indoleacetic Acids / Q000494:pharmacology*; D027845:Malus / Q000235:genetics* / Q000254:growth & development; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D040641:Quantitative Trait Loci
chemical_list: D007210:Indoleacetic Acids; D010940:Plant Proteins