Histone demethylase that demethylates 'Lys-27' (H3K27me) of histone H3 with a specific activity for H3K27me3 and H3K27me2, and involved in the regulation of gene expression (PubMed:25267112, PubMed:33324437). No activity on H3K27me1 (PubMed:25267112). Together with JMJ30, regulates the flowering-repressor FLOWERING LOCUS C (FLC) locus by removing the repressive histone modification H3 lysine 27 trimethylation (H3K27me3), especially at elevated temperatures (e.g. 29 degrees Celsius), thus preventing extreme precocious flowering (PubMed:25267112). JMJ30 and JMJ32 are regulators involved in the integration of abscisic acid (ABA) and brassinosteroids (BR) signaling pathways (PubMed:33324437). Together with JMJ30, controls ABA-mediated growth arrest during the post-germination stage in unfavorable conditions, and responses to ABA during root development, via the removal of repressive histone mark (H3K27me3) from the SnRK2.8 promoter, thus promoting SnRK2.8 expression and subsequent kinase-dependent ABI3 activation (PubMed:30859592, PubMed:30983495). In addition, removes the repressive histone marks (H3K27me3) from the BZR1 locus in response to stress and ABA, thus activating the BR signaling pathway which, in turn, inhibits the ABA signaling pathway (PubMed:33324437). 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 2 2-oxoglutarate + N(6),N(6),N(6)-trimethyl-L-lysyl(27)-[histone H3] + 2 O2 = 2 CO2 + 2 formaldehyde + N(6)-methyl-L-lysyl(27)-[histone H3] + 2 succinate Binds 1 Fe(2+) ion per subunit. Predominantly localized in the nucleus. Expressed ubiquitously including in vasculatures, leaves, siliques, roots and inflorescences (PubMed:25267112, PubMed:18713399). Present in the root meristem (PubMed:30859592). Accumulates in cotyledons and root tips of young seedlings (PubMed:33324437). No visible phenotype under normal growth conditions (PubMed:30859592). Reduced abscisic acid (ABA)-mediated growth arrest during the post-germination stage, with stronger effect in plants lacking both JMJ30 and JMJ32 (PubMed:30859592). The double mutant missing JMJ30 and JMJ32 exhibits an early-flowering phenotype at elevated temperatures (e.g. 29 degrees Celsius), associated with increased H3K27me3 levels at the FLC locus and decreased FLC expression (PubMed:25267112). The double mutant jmj30 jmj32 has longer primary roots (PubMed:30983495). In jmj30-2 jmj32-1 double mutants, reduced brassinosteroids (BR) mediated repression of ABA-inducible genes (e.g. ABI5, ABF2, ABF3 and ABF4) (PubMed:33324437). Belongs to the JARID1 histone demethylase family.