Deposition of histone variant H2A.Z by the SWR1 chromatin-remodeling complex is critical for the appropriate expression of many genes in eukaryotes, yet, despite its importance, the composition of the Arabidopsis SWR1 complex has not been thoroughly analyzed. Here we have identified the interacting partners of a conserved Arabidopsis SWR1 subunit, actin-related protein 6 (ARP6). We isolated 9 predicted components, identifying subunits implicated in histone acetylation and interacting partners implicated in chromatin biology. We found that the methyl-CpG-binding domain 9 (MBD9) subunit functioned synergistically with ARP6 to control flowering time. MBD9, in combination with ARP6, was involved in the SWR1-mediated incorporation of the majority of H2A.Z. MBD6 was further required for deposition of H2A.Z at a distinct subset of loci. MBD9 was preferentially bound to nucleosome-depleted regions at the 5' of genes containing high levels of activating histone marks. Our data suggests a model for MBD9 in recruiting the SWR1 complex to open chromatin of actively transcribing genes. Overall design: Total RNA was extracted from 13 DAG shoots grown on 1%MS supplemented with 1% sucrose under long day conditions. Four replicates, grown on separate plates were collected for each genotype. Each replicate conisted of three seedlings. RNA was extracted using Direct-zol RNA Miniprep kit (Zymo). For RNA-Seq, 1ug of total RNA was used to prepare libraries using the TrueSeq Stranded mRNA-Seq kit (Illumina).