Regulation of flowering time by SPL10/MED25 module in Arabidopsis

Several SQUAMASA PROMOTER BINDING PROTEIN-LIKE (SPL) transcription factors are involved in plant developmental transition from vegetative to reproductive growth. However, the function of SPL10 in regulating floral transition is largely unknown. It is also not known which Mediator subunit mediates SPL10 transcriptional activity. Here, we used overexpression lines and knockout mutants to examine the role of SPL10 in flowering-time regulation and we investigated possible interactions of SPL10 with several mediator subunits in vitro and in vivo. Plants overexpressing SPL10 showed precocious flowering, whereas the triple loss-of-function mutants of SPL10 and its two homologous genes, SPL2 and SPL11, flowered late compared with wild-type plants. We found that SPL10 interacts with MED25, a subunit of the Mediator complex, which bridges transcription factors and RNA polymerase II to facilitate transcription initiation. Genetic analysis showed that MED25 acts downstream of SPL10 to execute SPL10-regulated floral transition. Furthermore, SPL10 was required for MED25 association with the promoters of two target genes, FUL and LFY. We provide evidence that SPL10 recruits MED25 to the promoters of target genes to regulate flowering time. Our results on the SPL10/MED25 module are relevant to the molecular mechanism of other SPL family members.