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As a cell proliferation regulator involved in wide biological processes in plants, GRF-INTERACTING FACTOR (GIF) controls different tissues development. However, whether GIF participates in fruit development remains unclear. According to transcriptome data, we identified PbGIF1 was highly expressed during fruit development in cytokinins induced parthenocarpy pear. In the present study, the biofunction of PbGIF1 was initially verified. Overexpression of PbGIF1 promoted fruit size of transgenic tomato. The size of flesh fruit was not affected by cell expansion but the cell proliferation was promoted by overexpressing PbGIF1. The accelerated cell proliferation process was also observed in PbGIF1-overexpressed transgenic pear fruit calli. The transcriptional regulation of cytokinins on PbGIF1 was further confirmed by exogenous CPPU treatments in pear fruitlets. To investigate the underlying mechanism, the cytokinins-responded factor, PbRR1, was further focused on. The results of Yeast-one-hybrid assay suggested that PbRR1 can bind to the promoter sequence of PbGIF1. The transcriptional activation of PbRR1 on PbGIF1 was also confirmed by Dual-Luciferase assays. Taken together, the results showed that cytokinins control pear fruit development via the transcriptional activation of PbGIF1 by PbRR1.

The red flesh in apple fruit is a desired trait by consumers and it is associated to the anthocyanin content, which is mainly controlled by MdMYB10 with a R6 promoter. In this study, a high-density linkage group was constructed using the ‘Fuji’ x ‘Red3’ population which contained homozygous alleles R1R1 and R6R6, respectively. The linkage group consists of 7 630 SNPs along 17 linkage groups, spanning 2 270.21 cM, with an average density of 0.30 cM per marker. The cyanidin-3-galactoside concentration was used as the phenotypic data in QTL analysis. Moreover, one QTL peak which was flaked by two markers, marker2187260 to marker2173766, with LOD scores of 4.49 was detected. This QTL ranged from 0 to 40.79 cM on the top of linkage group (LG16). In addition one candidate molecular marker (marker2175442) in this QTL was identified, which was significant correlated with the flesh cyanidin-3-galactoside concentration. These genetic findings enrich the breeding basis of fruit flesh coloration in apple.

Dwarfing is an important agronomic characteristic in fruit breeding. However, due to the lack of dwarf cultivars and dwarf stocks, the dwarfing mechanism is poorly understood in pears. In this research, we discovered that the dwarf hybrid seedlings of pear (Pyrus bretschneideri Rehd.), ‘Red Zaosu,’ exhibited a xylem-deficient dwarf phenotype. The expression level of PbXND1, a suppressor of xylem development, was markedly enhanced in dwarf hybrid seedlings and its overexpression in pear results in a xylem-deficient dwarf phenotype. To further dissect the mechanism of PbXND1, PbTCP4 was isolated as a PbXND1 interaction protein through the pear yeast library. Root transformation experiments showed that PbTCP4 promotes root xylem development. Dual-luciferase assays showed that PbXND1 interactions with PbTCP4 suppressed the function of PbTCP4. PbXND1 expression resulted in a small amount of PbTCP4 sequestration in the cytoplasm and thereby prevented it from activating the gene expression, as assessed by bimolecular fluorescence complementation and co-location analyses. Additionally, PbXND1 affected the DNA-binding ability of PbTCP4, as determined by utilizing an electrophoretic mobility shift assay. These results suggest that PbXND1 regulates the function of PbTCP4 principally by affecting the DNA-binding ability of PbTCP4, whereas the cytoplasmic sequestration of PbTCP4 is only a minor factor. Taken together, this study provides new theoretical support for the extreme dwarfism associated with the absence of xylem caused by PbXND1, and it has significant reference value for the breeding of dwarf varieties and dwarf rootstocks of the pear.