Genome-Wide Identification and Expression Analysis of the fw2.2-like Gene Family in Pear

Fruit size is a major factor determining yield, quality, and consumer acceptability. fw2.2 (fruit weight-2.2) is a primary quantitative trait locus that was the first to be cloned, accounting for 30% of the variation in tomato fruit size. The various homologs of fw2.2 (fw2.2-like) have been identified in many plants and belong to a large family. To date, there has been no report that has carried out a comprehensive identification of fw2.2-like members in pear. In this study, a total of 14 fw2.2-like genes were identified in the pear (Pyrus bretschneideri Rehd) genome and designated as PbFWL1-14. All of the PbFWL genes were unevenly distributed on nine chromosomes, and each chromosome contained between one and four genes. All PbFWL proteins contained more than two conserved motifs, and PbFWL genes contained more than one intron, and the genes of the same subfamily seemed to have a similar intron gene structure. According to the neighbor-joining phylogenetic tree, a total of 78 fw2.2/CNR (cell number regulator) from five plant species, including pear, maize, tomato, peach, rice, and physalis, could be divided into seven subgroups, and PbFWL proteins were mainly distributed in subgroups 1, 3, 4, 5, and 6. The Ka/Ks analysis also revealed that the fw2.2-like gene family of pear may have been subjected to strong purifying selection pressure during its evolution. A cis-element analysis found that many cis-elements responsive to hormones and stress were discovered in promotion regions for all PbFWLs. When combining real-time quantitative PCR analysis detection results, PbFWL1/2/5 were found to be the most likely candidate genes for regulating pear fruit size.