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.

Expression Pattern of FT/TFL1 and miR156-Targeted SPL Genes Associated with Developmental Stages in Dendrobium catenatum.

Time to flower, a process either referring to juvenile-adult phase change or vegetative-reproductive transition, is strictly controlled by an intricate regulatory network involving at least both FT/TFL1 and the micro RNA (miR)156-regulated SPL family members. Despite substantial progresses recently achieved in Arabidopsis and other plant species, information regarding the involvement of these genes during orchid development and flowering competence is still limited. Dendrobium catenatum, a popular orchid species, exhibits a juvenile phase of at least three years. Here, through whole-genome mining and whole-family expression profiling, we analyzed the homologous genes of FT/TFL1, miR156, and SPL with special reference to the developmental stages. The FT/TFL1 family contains nine members; among them, DcHd3b transcribes abundantly in young and juvenile tissues but not in adult, contrasting with the low levels of others. We also found that mature miR156, encoded by a single locus, accumulated in large quantity in protocorms and declined by seedling development, coincident with an increase in transcripts of three of its targeted SPL members, namely DcSPL14, DcSPL7, and DcSPL18. Moreover, among the seven predicted miR156-targeted SPLs, only DcSPL3 was significantly expressed in adult plants and was associated with plant maturation. Our results might suggest that the juvenile phase change or maturation in this orchid plant likely involves both the repressive action of a TFL1-like pathway and the promotive effect from an SPL3-mediated mechanism.