PbGIF1 promoting cell-proliferation in pear fruit is transcriptionally activated by PbRR1

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.