Identification of flowering genes in Camellia perpetua by comparative transcriptome analysis

Camellia perpetua has the excellent characteristic of flowering multiple times throughout the year, which is of great importance to solve the problem of “short flowering period” and “low fresh flower yield” in the yellow Camellia industry at present. Observations of flowering phenology have demonstrated that most floral buds of C. perpetua were formed by the differentiation of axillary buds in the scales at the base of the terminal buds of annual branches. However, the molecular mechanism of flowering in C. perpetua is still unclear. In this study, we conducted a comparative transcriptomic study of the terminal buds and their basal flower buds in March (spring) and September (autumn) using RNA-seq and found that a total of 11,067 genes were significantly differentially expressed in these two periods. We identified 27 genes related to gibberellin acid (GA) synthesis, catabolism, and signal transduction during floral bud differentiation. However, treatment of the terminal buds and axillary buds of C. perpetua on annual branch with GA3 did not induce floral buds at the reproductive growth season (in August) but promoted shoot sprouting. Moreover, 203 flowering genes were identified from the C. perpetua transcriptome library through homology alignment, including flowering integrators LEAFY (LFY) and UNUSUAL FLORAL ORGANS (UFO), as well as MADS-box, SQUAMOSA PROMOTER BINDING PROTEIN-box (SBP-box), and TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR (TCP) genes, which were specifically upregulated in floral buds and were likely involved in flowering in C. perpetua. The floral inhibitor CperTFL1b was identified and cloned from C. perpetua, and its expression level was specifically regulated in terminal buds in autumn. Ectopic overexpression of CperTFL1b delayed flowering time and produced abnormal inflorescence and floral organs in Arabidopsis, suggesting that CperTFL1b inhibits flowering. In conclusion, this study deepens our understanding of the molecular mechanism of blooms throughout the year in C. perpetua and provides a helpful reference for cultivating new varieties of yellow Camellia with improved flowering traits.