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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 anAuxin 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.

Item Type:	Article
Authors/Creators:	Devoghalaere, F and Doucen, T and Guitton, B and Keeling, J and Payne, W and Ling, TJ and Ross, JJ and Hallett, IC and Gunaseelan, K and Ga, D and Diack, R and Breen, KC and Tustin, DS and Costes, E and Chagne, D and Schaffer, RJ and David, KM
Journal or Publication Title:	BMC Plant Biology
ISSN:	1471-2229
DOI / ID Number:	https://doi.org/10.1186/1471-2229-12-7
Additional Information:	Licenced under Creative Commons License Deed Attribution 2.0 Generic (CC BY 2.0)
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