TEM1 combinatorially binds to <i>FLOWERING LOCUS T</i> and recruits a Polycomb factor to repress the floral transition in <i>Arabidopsis</i>.

Abstract

<i>Arabidopsis</i> TEMPRANILLO 1 (TEM1) is a transcriptional repressor that participates in multiple flowering pathways and negatively regulates the juvenile-to-adult transition and the flowering transition. To understand the molecular basis for the site-specific regulation of <i>FLOWERING LOCUS T</i> (<i>FT</i>) by TEM1, we determined the structures of the two plant-specific DNA-binding domains in TEM1, AP2 and B3, in complex with their target DNA sequences from the <i>FT</i> gene 5'-untranslated region (5'-UTR), revealing the molecular basis for TEM1 specificity for its DNA targets. In vitro binding assays revealed that the combination of the AP2 and B3 binding sites greatly enhanced the overall binding of TEM1 to the <i>FT</i> 5'-UTR, indicating TEM1 combinatorically recognizes the <i>FT</i> gene 5'-UTR. We further showed that TEM1 recruits the Polycomb repressive complex 2 (PRC2) to the <i>FT</i> 5'-UTR. The simultaneous binding of the TEM1 AP2 and B3 domains to <i>FT</i> is necessary for deposition of H3K27me3 at the <i>FT</i> 5'-UTR and for the flowering repressor function of TEM1. Overall, our data suggest that the combinatorial recognition of <i>FT</i> 5'-UTR by TEM1 ensures H3K27me3 deposition to precisely regulate the floral transition.