The WD-40 repeat-containing protein CmRACK1 negatively regulates chrysanthemum flowering in response to photoperiod and gibberellin signaling

Chrysanthemums are typical short-day plants, and photoperiod and gibberellic acid (GA) signal perception and transduction are the key factors regulating flowering in the chrysanthemum. The function and molecular mechanism undertaken by the receptors for activated C kinase 1 (RACK1) protein to regulate chrysanthemum flowering are currently unclear. Here, we isolated CmRACK1 from chrysanthemum. We found that CmRACK1 was induced by the photoperiod and exhibited rhythmic expression characteristics. Compared with the wild-type, the CmRACK1 overexpression lines showed delayed flowering, while the artificial micro RNA (amiRNA)-mediated knockdown lines showed early flowering. Transcriptome analysis of CmRACK1 transgenic and wild-type lines revealed differential expression of GIBBERELLIC ACID INSENSITIVE DWARF 1B (GID1B), gibberellin 20-oxidase 1, and gibberellin 3-oxidase 1. Quantification of gibberellin levels in transgenic and wild-type plants indicated a significant decrease in GA1 content in the CmRACK1 overexpression lines and a notable increase in the knockdown lines. We conducted dual-luciferase reporter assays in Nicotiana benthamiana leaves and found that CmRACK1 stimulates the expression of CmGID1B, thereby negatively regulating chrysanthemum flowering via the gibberellin signaling pathway. Our research findings provided a foundation for understanding the molecular mechanisms underlying flowering time regulation in chrysanthemum.