An unexpected candidate gene may be involved in the control of fruit acidity in peach

Laburpena

Acidity is one of the major components of fleshy fruit taste and was attributed to the D locus in peach. The D locus was mapped to the top of linkage group (LG) 5 by using a progeny derived from the cross between the sub acid cultivar ‘Ferjalou Jalousia®’ (D/D) and the acid cultivar ‘Fantasia’ (d/d). The D locus was delimited to a genetic interval of 0.4 cM corresponding to a DNA fragment of 100 kb. Two BAC clones, each corresponding to an allele were sequenced. Using the peach annotated genome sequence as a reference, 9 potential genes were located in this region. To our knowledge, none of them are known to be involved in the control of fruit acidity. Differential expression analysis of RNA-Seq data generated from fruits sampled at different stages of development from ‘Ferjalou Jalousia®’ and ‘Fantasia’ revealed 17 genes with significant differential expression on LG5, but only oneof them located in the D locus. The expression of this gene was significantly higher in the ‘Ferjalou Jalousia®’ than in the ‘Fantasia’ fruits. This gene potentially encodes a protein with high similarity to Glucan endo-1,3-beta-glucosidase (GebG). Comparative analysis of the two allele sequences of the GebG gene and its surrounding intergenic sequences revealed an insertion/deletion in a tandem repeat sequence localized upstream of the transcription initiation start site. Analysis of this region in a panel of peach trees producing acid and sub-acid fruits showed a highly significant association between the insertion and the low acidity of the fruit. This tandem repeat sequence could be -involved in the transcriptional regulation of GebG. qRT-PCR analysis of GebG expression along the development of peach fruits confirmed the results of RNA-Seq analysis and revealed spatial and temporal control of GebG expression. All these results strongly suggest that GebG may play a major role in the control of fruit acidity in peach.