Genome-Wide Characterization of the VfBES1 Gene Family in Vernicia fordii Unveils Lineage- Specific Regulatory Innovations in Floral Development

Background The Tung tree ( Vernicia fordii Hemsl.), a commercially significant oil-producing tree species. However, the molecular mechanisms governing floral sex determination remain elusive, particularly the genetic basis underlying the skewed female-to-male flower ratio and the evolutionary dynamics of sex-related gene families, which severely restricts targeted breeding for yield enhancement. The BES1 transcription factor family, which plays a crucial role in Brassinosteroid (BR) signaling and reproductive development, is particularly underexplored in woody perennials. Results In this study, we introduce the first genome-wide identification and functional characterization of the VfBES1 gene family in the Tung tree. Integrative multi-omics approaches have revealed seven VfBES1 genes, clustered into three phylogenetically distinct clades, each characterized by lineage-specific motifs and structural simplicity. Segmental duplication events ( VfBES1-1 / VfBES1-5 and VfBES1-4 / VfBES1-7 ) and promoter cis-element enrichment (hormone-responsive and abiotic stress-related motifs) highlight evolutionary innovation and functional diversification. Spatiotemporal expression profiling reveals tissue- and stage-specific roles: VfBES1-1 was predominantly expressed in female flowers and fruits, suggesting potential involvement in sex determination. Conversely, VfBES1-2 and VfBES1-6 exhibited male flower-specific and early floral developmental activation, respectively. Nuclear-localized VfBES1-6 displayed co-expression with VfMYB35-1 , a regulator of male structure degeneration, although no direct interaction was detected. Conclusions These findings shed light on the regulation of VfBES1s in floral development, offering a reference for precision breeding to enhance flowering synchrony and seed productivity in the Tung tree. This study provides a comparative framework for understanding lineage-specific BES1 functions in non-model woody plants.