Comprehensive Analysis of Boron-Induced Changes in Cell Expansion and Phytohormone During Early Ovary Development in Pear (Pyrus sinkiangensis Yu)

Boron exerts regulatory control over various aspects of plant growth and morphogenesis, and the application of boron prior to anthesis has been recognized as a critical agronomic practice. However, the regulatory mechanisms by which boron influences fruit set and early ovary development in pear remain to be elucidated. In this study, boron application was used at three stages, including pre-flowering, full-flowering, and early fruiting in the 'Kuerle Xiangli' (<i>Pyrus sinkiangensis</i> Yu), with a focus on cell expansion and endogenous phytohormone. As a result, treatment with 0.3% boric acid significantly increased endogenous boron concentrations in both leaves and ovaries and enhanced ovary fresh weight as well as both longitudinal and transverse diameters. Histological analysis revealed pronounced cell expansion at 5, 10, and 15 days after pollination (DAP) following boron treatment. Furthermore, gibberellin and trans-zeatin concentrations at 5 and 10 DAP were significantly elevated, while the concentrations of abscisic acid and auxin were markedly reduced. Quantitative real-time PCR (qRT-PCR) analysis demonstrated that boron positively regulates the expression of auxin-related genes, like <i>PbARFH</i>, <i>PbARFD</i> and <i>PbSAUR76-like</i>. In the gibberellin signaling pathway, the expression <i>PbGID1</i>, <i>PbGID1C-like</i> and <i>PbGID2</i> was activated to drive cell expansion with the boron application. In the abscisic acid signaling pathway, boron treatment induced downregulation of <i>PbSRK2.4</i>, <i>PbABF2</i>, and <i>PbABF2-like</i> in the ovary. Furthermore, boron treatment induced high expression of hormone signaling genes in cytokinin, brassinolide, jasmonic acid and salicylic acid signaling pathways. These findings provide insights into the mechanisms of cell expansion and hormonal changes by which boron modulates early ovary development, offering a basis for improving fruit quality through optimized boron application.