Molecular cloning and expression analysis of the WEE1 and CCS52A genes in European pear (Pyrus communis l.) and their possible roles in a giant fruit mutant

A giant-fruited mutant of European pear (Pyrus communis L.), Giant La France (GLaF), that arose from a bud sport of normal ‘La France’, exhibited receptacle-specific DNA reduplication resulting in an approx. 1.6-fold increase in fruit size compared with normal ‘La France’ fruit. To identify the genes responsible for this receptacle-specific DNA reduplication, we focussed on the regulatory genes WEE1 and CCS52A, which have been reported to increase the ploidy level of tomato fruit flesh. Full-length cDNAs of WEE1 and CCS52A, referred to as PcWEE1 and PcCCS52A, were cloned from P. communis L., ‘La France’. We determined the genomic sequences of these two genes, clarified their exon-intron structures, and compared cDNA sequences between ‘La France’ and GLaF. The predicted amino acid sequences were similar to other species and retained their conserved domains. No differences were found between the PcWEE1 and PcCCS52A cDNA sequences of ‘La France’ and GLaF. However, analysis revealed that the levels of expression of PcWEE1 and PcCCS52A were higher in the receptacles of GLaF than in those of ‘La France’ 1 week before the full-bloom stage. Our results suggest that PcWEE1 and PcCCS52A may play important roles in the occurrence and persistence of DNA reduplication in the receptacles, and hence fruit, of GLaF.