Cloning, localization and expression analysis of two fw2.2-like genes in small- and large-fruited pear species

Fruit size is one of the most important agronomic characters, which is mainly determined by cell number and cell size. However, our current knowledge about pear is largely unknown. Through counting of pear mesocarp cells at different stages, we found that the cell number, rather than the cell size, is responsible for the differences between small- and large-fruited cultivars. Fruit weight-2.2 (fw2.2) is an important quantitative trait locus (QTL) affecting fruit weight in tomato and functions as a negative regulator in carpel cell division. To get more insights into this QTL in pear fruit development, we isolated two putative homologous fw2.2 genes, which were designated as fw2.2-like (PbFWL) genes. PbFWLs encode Cys-rich proteins with the CCXXXXCPC motif and belong to the PLAC8 superfamily. In addition, results from the subcellular localization indicated that PbFWLs were localized in the plasma membrane. The expression profile of the PbFWL genes by qRT-PCR showed they expressed higher in small-sized fruit cultivar than that in large-sized fruit cultivar during the cell division period. In summary, our data suggest that these two PbFWLs might be negatively related to the cell division in pear fruit.