LIKE HETEROCHROMATIN PROTEIN 1 (LHP1) partially inhibits the transcriptional activation of FT by MYB73 and regulates flowering in Arabidopsis

SUMMARY Polycomb group (PcG) proteins are essential gene repressors in higher eukaryotes. However, how PcG proteins mediate transcriptional regulation of specific genes remains unknown. LIKE HETEROCHROMATIN PROTEIN 1 (LHP1), as a component of Polycomb Repression Complexes (PRC), epigenetically mediates several plant developmental processes together with PcG proteins. We observed physical interaction between MYB73 and LHP1 in vitro and in vivo. Genetic analysis indicated that myb73 mutants showed slightly late flowering, and the lhp1‐3 myb73‐2 double mutant exhibited delayed flowering and downregulated FT expression compared to lhp1‐3. Chromatin immunoprecipitation and yeast one‐hybrid assays revealed that MYB73 preferentially binds to the FT promoter. Additionally, our protoplast transient assays demonstrated that MYB73 activates to the FT promoter. Interestingly, the LHP1‐MYB73 interaction is necessary to repress the FT promoter, suggesting that the LHP1‐MYB73 interaction prevents FT activation by MYB73 in Arabidopsis. Our results show an example in which a chromatin regulator affects transcriptional regulation by negatively regulating a transcription factor through direct interaction. Significance Statement A flowering mechanism was prominent in various plants. FT plays a crucial regulator in the flowering mechanism. It is essential to uncover the FT regulation mechanisms to regulate the flowering time in plants. We described here how to regulate FT expression by MYB73 and LHP1 via protein–protein interaction. MYB73 associates with the FT promoter and activates FT expression. However, LHP1 interaction with MYB73 inhibits MYB73‐mediated FT activation in Arabidopsis.