TOUSLED KINASE INTERACTING PROTEIN 1 (TKI1) interacts with SIN3-LIKES (SNLs) to promote flowering in Arabidopsis

TOUSLED KINASE INTERACTING PROTEIN 1 (TKI1) is a SANT/Myb domain-containing protein, which binds DNA and may function as a transcription factor, and is characterized as an interacting protein with TOUSLED (TSL) in Arabidopsis. However, it remains largely unknown what biological functions of TKI1 for few reports about TKI1 in the literature. Here we first identified that TKI1 interacts with SIN3-LIKEs (SNLs) and the responsible interaction domains are the C-terminal domain of TKI1 and the PAH (Paired Amphipathic Helix) domains of SNLs respectively in yeast. Then, we further confirmed the interactions between TKI1 and SNLs (SNL1-SNL6) in vitro or in vivo using multiple different protein-protein interaction methods. In addition, TKI1 and SNL3 are co-expressed in all the examined tissues here, and TKI1 and SNL3 are co-localized in the nucleus, indicating they may function together in plant. Furthermore, Genetic analysis with knockout mutants showed that both TKI1 and SNLs promote flowering with an additive effect in long days (LDs), however TKI1 induces flowering but SNLs inhibit flowering in short days (SDs). Finally, the flowering repressor FLOWERING LOCUS C (FLC) and its homolog MADS AFFECTING FLOWERING 4 (MAF4) were up-regulated, and the flowering activator FLOWERING LOCUS T (FT) and CONSTANS (CO) were down-regulated in tki1, snl1/2/3/4/5 and snl1/2/3/4/5 tki1 mutants, compared with Col-0. Therefore, our results increase our understanding of the biological functions of TKI1, and reveal that TKI1 physically interacts with SNLs and they both induce flowering in LDs, and indicate that TKI1 and SNLs may function together to regulate flowering gene expression to promote flowering in Arabidopsis.