Flowering repressor CmSVP recruits the TOPLESS corepressor to control flowering in chrysanthemum

Plant flowering time is induced by environmental and endogenous signals perceived by the plant. The MCM1-AGAMOUSDEFICIENS-Serum Response Factor-box (MADS-box) protein SHORT VEGETATIVE PHASE (SVP) is a pivotal repressor that negatively regulates the floral transition during the vegetative phase; however, the transcriptional regulatory mechanism remains poorly understood. Here, we report that CmSVP, a chrysanthemum (Chrysanthemum morifolium Ramat.) homolog of SVP, can repress the expression of a key flowering gene, a chrysanthemum FLOWERING LOCUS T-like gene (CmFTL3), by binding its promoter CArG element to delay flowering in the ambient temperature pathway in chrysanthemum. Protein-protein interaction assays identified an interaction between CmSVP and CmTPL1-2, a chrysanthemum homologue of TOPLESS (TPL) that plays critical roles as transcriptional corepressor in many aspects of plant life. Genetic analyses revealed the CmSVP-CmTPL1-2 transcriptional complex is a prerequisite for CmSVP to act as a floral repressor. Furthermore, overexpression of CmSVP rescued the phenotype of the svp-31 mutant in Arabidopsis (Arabidopsis thaliana), overexpression of AtSVP or CmSVP in the Arabidopsis dominant-negative mutation tpl-1 led to ineffective late flowering, and AtSVP interacted with AtTPL, confirming the conserved function of SVP in chrysanthemum and Arabidopsis. We have validated a conserved machinery wherein SVP partially relies on TPL to inhibit flowering via a thermosensory pathway.