Histone demethylase that demethylates 'Lys-27' (H3K27me) of histone H3, thus acting as a positive regulator of gene expression (PubMed:33107825). Demethylates both tri- (H3K27me3) and di-methylated (H3K27me2) H3K27me (PubMed:21642989, PubMed:27111035, PubMed:33107825). Demethylates also H3K4me3/2 and H3K36me3/2 in an in vitro assay (PubMed:20711170). Involved in the transcriptional regulation of hundreds of genes regulating developmental patterning and responses to various stimuli (PubMed:18467490). Binds DNA via its four zinc fingers in a sequence-specific manner, 5'-CTCTG(C/T)T(C/T)-3' (5'-CTCTGYTY-3'), with a preference for hypo-methylated status (e.g. cytosine methylation), to promote the demethylation of H3K27me3 and recruit the chromatin remodeler BRM in order to activate gene expression (PubMed:27111034, PubMed:27111035, PubMed:32257379, PubMed:31048693). Participates in the regulation of organ boundary formation (PubMed:27111034, PubMed:27111035, PubMed:32257379, PubMed:31048693). Bind mostly motifs located in active chromatin states which are depleted for heterochromatic modifications (PubMed:31048693). Involved in the regulation of flowering time by repressing FLOWERING LOCUS C (FLC) expression (PubMed:15377760, PubMed:33107825, PubMed:32392578). Stimulates lateral roots formation (e.g. primordium initiation and emergence) via the epigenetic de-repression of PIN genes such as PIN1, PIN3 and PIN7 directly by modulating the methylation status of their loci (PubMed:30267471). Interacts with the NF-Y complex to regulate SOC1 (PubMed:25105952). Mediates the recruitment of BRM to its target loci (PubMed:27111034). Together with EEN, involved in the epigenetic chromatin-dependent regulatory mechanism that monitors the expression of the essential multifunctional plant stress regulator EIN2 via H3K27me3 repressive histone demethylation and histone variant H2A.Z eviction, thus modulating responses to ethylene (ET), especially during embryogenesis (PubMed:31418686). Eluviates seed dormancy by triggering abscisic acid (ABA) catabolism in seeds via the induction of CYP707A1 and CYP707A3 expression, genes involved in ABA degradation; binds directly to CYP707A1 and CYP707A3 loci to reduce their H3K27me3 levels in developing siliques (PubMed:33037128). Required for systemic acquired resistance (SAR) toward pathogenic bacteria (e.g. Pseudomonas syringae pv tomato DC3000 (avrPto)) (PubMed:32392578). Together with FLD and MSI4/FVE, contributes to dehydroabietinal-dependent (DA, a diterpenoid tricyclic diterpene) activation of flowering ans SAR (PubMed:32392578). Binds to the HSFA2 chromatin region to alleviate H3K27me3 repressive marks and trigger its expression in response to heat in a BRM-dependent manner (PubMed:30778176). Involved in the mechanisms necessary for quick response to heat and subsequent heritable transgenerational memory of heat acclimation (global warming) such as early flowering and attenuated immunity; this process includes epigenetic regulation as well as post-transcriptional gene silencing (PTGS) (PubMed:30778176). In response to heat, HSFA2 is activated and promotes the expression of REF6 which in turn derepresses HSFA2, thus establishing an heritable feedback loop able to trigger SGIP1 and subsequent SGIP1-mediated SGS3 degradation; this prevents the biosynthesis of trans-acting siRNA (tasiRNA) and leads to the release of HTT5, which drives early flowering but attenuates immunity (PubMed:30778176). Involved in the maintenance of H3K27me1 histone marks on euchromatin in a PRC2-dependent manner, to maintain low-level basal expression of corresponding genes (PubMed:33107825). Together with ELF6, required for H3K27me3 resetting (especially in constitutive heterochromatin within the pericentromeric regions) and transgenerational inheritance of histone marks, thus acting in safeguarding genome and epigenome integrity during sexual reproduction (PubMed:33107825). 2-oxoglutarate + N(6),N(6),N(6)-trimethyl-L-lysyl(27)-[histone H3] + O2 = CO2 + formaldehyde + N(6),N(6)-dimethyl-L-lysyl(27)-[histone H3] + succinate 2-oxoglutarate + N(6),N(6)-dimethyl-L-lysyl(27)-[histone H3] + O2 = CO2 + formaldehyde + N(6)-methyl-L-lysyl(27)-[histone H3] + succinate Forms homooligomers (PubMed:32257379). Interacts with BZR2 (via N-terminus) (PubMed:18467490). Interacts with BRM in the SWI/SNF complex (PubMed:27111034). Interacts (via N-terminus) with NFYC9 (PubMed:25105952). Associates with INO80 (PubMed:31418686). Highly expressed in the shoot apical meristem and primary and secondary root tips, and lower expression in cotyledons, leaves and root axis along vascular tissues (PubMed:30267471). Detected in inflorescences, stems and siliques. Present in seeds (PubMed:33037128). Accumulates during seed development, seed storage, and seed germination stages (PubMed:33037128). In roots, highly expressed in the stele, but barely detectable in the cortex and epidermis (PubMed:30267471). Not observed in lateral root primordia, but detected in both young and mature lateral roots (PubMed:30267471). Induced by abscisic acid (ABA) during seed germination (PubMed:33037128). Induced by dehydroabietinal-dependent (DA), a diterpenoid tricyclic diterpene that promotes flowering and systemic acquired resistance (SAR) (PubMed:32392578). Up-regulated by heat stress (at 30 degrees Celsius) and remains up-regulated transgenerationally in the unstressed progeny (at 22 degrees Celsius), partly via an heritable feedback loop involving HSFA2 (PubMed:30778176). The 4 C2H2-type zinc fingers are required for DNA-binding, but dispensable for the H3K27me3/2 demethylase activity. Late-flowering in both long and short days with an increased number of rosette leaves at bolting stage (PubMed:15377760, PubMed:33107825, PubMed:32392578). Brassinosteroid-insensitive phenotype (PubMed:18467490). Hyper-methylated genes with accumulation of H3K27me3 histone marks, but drastic reduction in H3K27me1 (PubMed:33107825). Enhanced dormancy associated with increased abscisic acid (ABA) levels as well as reduced expression of CYP707A1 and CYP707A3 (due to higher H3K27me3 content at their loci), genes involved in ABA catabolism, during seed development and germination (PubMed:33037128). Suppressed expression of PIN genes (e.g. PIN1, PIN3 and PIN7) due to increased levels of H3K27me3 at their loci and leading to altered lateral root formation and elongation (PubMed:30267471). Impaired systemic acquired resistance (SAR) toward pathogenic bacteria (e.g. Pseudomonas syringae pv tomato DC3000 (avrPto)) (PubMed:32392578). Lost ability of dehydroabietinal-dependent (DA, a diterpenoid tricyclic diterpene) to trigger flowering and systemic acquired resistance (SAR) (PubMed:32392578). Elevated H3K27me3 levels at HSFA2 locus associated with a reduced expression of HSFA2 and altered thermo-responsiveness and thermomemory of flowering (PubMed:30778176). Plants lacking both REF6 and ELF6 have several growth defects, such as increased number of petals, reduced silique length, embryos with patterning defects, and pleiotropic defects in leaf morphology, such as serrations and downward curling; these defects are caused by epimutations arising in offspring lineage due to a lack of H3K27me3 resetting during sexual reproduction (PubMed:33107825). Plants missing both EEN and REF6/EIN6 (e.g. ref6-1 een-2 and ein6-1 een-1), as well as double mutants ref6-1 ino80-1 and ref6-1 arp5-1, are insensitive to ethylene (ET) and exhibit reduced levels of EIN2 associated with a shift of the chromatin landscape to a repressive state at its locus (e.g. H3K27me3 and H2A.Z) (PubMed:31418686). Belongs to the JHDM3 histone demethylase family. According to some authors, recombinant REF6 can demethylate H3K4me3/2 and H3K36me3/2 (PubMed:20711170). In contrast, PubMed:21642989 and PubMed:27111035 show that REF6 is an intrinsic H3K27me3/2-specific demethylase. The different activities seen may be caused by the presence of different cofactors.