Dynamic metabolic and transcriptomic profiling reveal regulation of auxin signal transduction in Xanthoceras sorbifolium bunge pistil development

Xanthoceras sorbifolium Bunge is a woody oil tree species of significant economic value in north China. However, the imbalance in the sex ratio caused by the abortion of pistils in male flowers has limited the yield, and poses a constraint on the development of related industries. Based on the lab’s prior finding that IAA promotes pistil development, this study used morphological, transcriptomic, and metabolomic approaches to explore the auxin-mediated regulatory mechanisms. First, paraffin sectioning was employed to identify the critical stages of pistil development, providing a morphological basis for subsequent omics analyses. A total of 239 DEGs involved in the plant hormone signal transduction pathway were identified, among which 49 (accounting for approximately 1/5) were auxin-related—far more than the number of DEGs associated with other hormones. A total of 71 differentially accumulated metabolites (DAMs) were detected. Notably, the IAA content in the pistils of female flowers was consistently and significantly higher than that in male flower pistils, and this content showed an upward trend as pistil development progressed. Correlation analysis revealed that the regulatory effect of auxin is primarily associated with ethylene (ETH) and cytokinins (CK). A regulatory model was proposed: auxin synergizes with ETH/CK to drive female pistil development; male flowers showed lower ACC/ethylene-related metabolite signal consistent with altered ethylene-related profiles and have insufficient IAA/CK, causing pistil abortion. This study lays a foundation for elucidating the molecular mechanism by which auxin regulates pistil development in X. sorbifolium, and provides targets for the molecular regulation of its sex ratio.