Transcriptome analysis of flower receptacles of the European pear (Pyrus communis L.)'La France' and its giant fruit sport using next-generation sequencing technology

We studied Giant La France (GLaF), a sport that sets large fruit and that appeared spontaneously on a European pear (Pyrus communis L.) 'La France' tree. It is known that GLaF exhibits DNA reduplication, specifically in the receptacle, before full bloom. To identify the genes related to DNA reduplication in GLaF, we performed 454 pyrosequencing to obtain mRNA sequences from GLaF and 'La France' and to examine their levels of expression. In total, 1,166,675 sequences were obtained from the poly(A)-enriched complimentary DNA libraries of GLaF and 'La France' and assembled into 49,181 contigs. A further 78,431 sequences were obtained as singletons. Comparisons of the total RNA sequence abundance between GLaF and 'La France' revealed that the levels of expression of 26 genes changed significantly in GLaF. However, none of these genes had an obvious functional role that could explain the difference in fruit size between the GLaF sport and 'La France'. We also identified 61 core cell cycle genes by transcriptome analysis, but their involvement in the larger fruit size of GLaF remains to be elucidated. This study presents the first large-scale RNA sequence database for European pear using next-generation sequencing technology.The results obtained can assist in various studies concerning pear physiology, including clarification of the molecular basis for the GLaF sport mutation.