Abstract
BACKGROUND: Flower size significantly influences the visitation of pollinators in angiosperms, and is also a crucial trait that affects commercial value of ornament plants. Sweet osmanthus (Osmanthus fragrans) is an ornamental species characterized by its small and aromatic flowers. GATA transcription factors have been reported to be involved in regulating plant development and growth. However, our understanding of the regulatory functions of GATA transcription factors concerning floral traits in ornamental plants such as sweet osmanthus remains limited. RESULTS: In this study, we functionally identified a member of the GATA family,, designated as OfGATA9, in sweet osmanthus. The expression of OfGATA9 was found to be transcriptionally up-regulated during the early stages of flower opening in sweet osmanthus. Furthermore, the expression pattern of OfGATA9 correlated with the flower size across various cultivars of sweet osmanthus. The nucleus-localized OfGATA9 harbors a conserved GATA-type zinc finger domain, and belongs to subfamily I of the GATA family. Ectopic over-expression of OfGATA9 in Nicotiana tabacum resulted in an increase in both flower size and epidermis cell dimensions. Comparative transcriptome analysis between control and transgenic N. tabacum showed that over-expressing OfGATA9 led to differential expression of genes including EXLB1, XTHs, bHLHs, EFRs, Auxin/IAAs, SAURs, MYB-like, and MADS-box genes in flowers. CONCLUSIONS: This study revealed the function of OfGATA9 in regulatory networks that influence flower size by promoting cell expansion and the expression of related genes. Our findings establish a theoretical foundation for breeding large-flowered sweet osmanthus.