A transcriptional repression motif in the MADS factor AGL15 is involved in recruitment of histone deacetylase complex components

AGAMOUS-like 15 (AGL15) encodes a MADS-domain transcription factor that is preferentially expressed in the plant embryo. A number of direct downstream targets of AGL15 have been identified, and although some of these target genes are induced in response to AGL15, others are repressed. Additionally, direct target genes have been analyzed that exhibit strong association with AGL15 in vivo, yet in vitro AGL15 binds only weakly. These data suggest that AGL15 may form complexes with other proteins, thus modulating the specificity and function of AGL15 in planta. Here we report that AGL15 interacts with members of the SWI-independent 3/histone deacetylase (SIN3/HDAC) complex, and that AGL15 target genes are also responsive to an AGL15 interacting protein that is also a member of this complex, SIN3-associated polypeptide of 18 kDa (SAP18). AGL15 can repress transcription in vivo, and a region essential to this repressive function contains a motif that is conserved among putative orthologs of AGL15. This motif mediates the association of AGL15 with SAP18, thus providing a possible mechanism for the role of AGL15 in regulating gene expression via recruitment of an HDAC complex.