Histological, hormonal and transcriptomic reveal the changes upon gibberellin-induced parthenocarpy in pear fruit

Phytohormones play crucial roles in fruit set regulation and development. Here, gibberellins (GA(4+7)), but not GA(3), induced pear parthenocarpy. To systematically investigate the changes upon GA(4+7) induced pear parthenocarpy, dynamic changes in histology, hormone and transcript levels were observed and identified in unpollinated, pollinated and GA(4+7)-treated ovaries. Mesocarp cells continued developing in both GA(4+7)-treated and pollinated ovaries. In unpollinated ovaries, mesocarp cells stopped developing 14 days after anthesis. During fruit set process, GA(4+7), but not GA(1+3), increased after pollination. Abscisic acid (ABA) accumulation was significantly repressed by GA(4+7) or pollination, but under unpollinated conditions, ABA was produced in large quantities. Moreover, indole-3-acetic acid biosynthesis was not induced by GA(4+7) or pollination treatments. Details of this GA-auxin-ABA cross-linked gene network were determined by a comparative transcriptome analysis. The indole-3-acetic acid transport-related genes, mainly auxin efflux carrier component genes, were induced in both GA(4+7)-treated and pollinated ovaries. ABA biosynthetic genes of the 9-cis-epoxycarotenoid dioxygenase family were repressed by GA(4+7) and pollination. Moreover, directly related genes in the downstream parthenocarpy network involved in cell division and expansion (upregulated), and MADS-box family genes (downregulated), were also identified. Thus, a model of GA-induced hormonal balance and its effects on parthenocarpy were established.