Bee-mediated pollination enhances fruit set and seed yield in <i>Paeonia ostii</i> ‘Fengdan’: insights into physiological and molecular mechanisms

Bee pollination enhances crop productivity and food security globally. However, its impact on pollen performance within pistil tissues and the underlying regulatory mechanisms remain unclear. In this study, artificial self-pollination yielded the highest pollen deposition on stigmas (119879.33 ± 43037.92 grains), followed by bee pollination (95464.60 ± 3985.01 grains). Conversely, bee pollination achieved the highest seed set rate (55.21% ± 1.84%), significantly exceeding the artificial self-pollination rate (7.27% ± 1.87%). A positive correlation was observed between pollen load on the stigmatic pollination band and seed set rate. Bee pollination delivers ample high-quality pollen to the stigmas of oil tree peony, enhancing seed production. Moreover, a trend high correlation was observed between pollen deposition on the stigmatic pollination band and seed set rate. Fluorescence microscopy and endogenous hormone analyses revealed that bee pollination stimulated a rapid increase in ZR, IAA, and GA₃ levels in the pistil tissues, promoting pollen germination and pollen tube growth. Transcriptome analysis identified <i>PoFAR2</i>, a key candidate gene involved in pollen development, in the pistil tissues after bee pollination. This gene exhibits high homology with genes found in other crops. The <i>PoFAR2</i> gene localizes to the cell membrane, validating earlier predictions, and exhibits strong transcriptional activity. Silencing <i>PoFAR2</i> disrupts pollen development in <i>Paeonia ostii</i> 'Fengdan' manifesting as structural defects in pollen walls and significantly reduces pollen viability. In conclusion, bees enhance fertilization in oil tree peony by delivering high-quality pollen that promotes germination and pollen tube growth. Crucially, we identified <i>PoFAR2</i>, a membrane-localized key gene regulating pollen development. This study establishes a crucial foundation for deciphering the molecular mechanisms by which bee pollination and phytohormone signaling mediate pollen development.