Binds to the promoter and regulates the transcription of target genes, maintaining them in an active state; at promoters, required for TATA binding proteins (TBPs, e.g. TBP1 and TBP2) and RNA polymerase II (Pol II) recruitment, and, in a subsequent event, is recruited by a phosphorylated form of Pol II to the +300-bp region of transcribed sequences to trimethylates nucleosomes. Histone trimethyltransferase that trimethylates 'Lys-4' of histone H3 (H3K4me3); H3 'Lys-4' methylation represents a specific tag for epigenetic transcriptional activation and is required for efficient elongation of transcription but not for transcription initiation. Methylates only a limited fraction of nucleosomes of target genes (e.g. FLC, NAP, XTH33 and WRKY70). Necessary for WDR5A occupancy at WRKY70 and LTP7 genes. Required to maintain the active state of class A (AP1 and AP2), class B (PI and AP3) and class C (AG, AGAMOUS) floral homeotic genes at early stages of flower development. Together with CLF, modulates AG nucleosome methylation statement. Involved in epigenetic regulation (e.g. H3K4me3) of the floral repressors FLC, FT and SOC1 to prevent the transition from vegetative to reproductive development, independently of the photoperiod; binds the active FLC locus before flowering, but this interaction is released upon the transition to flowering. Regulates floral organ identity and flowering transition. Functions as a receptor for the lipid messenger phosphatidylinositol 5-phosphate (PI5P), which regulates negatively its transcriptional activation activity. Exhibits histone methylase activity and subsequent transcriptional regulation on WRKY70 gene, and, to a lower extent on secondary defense-response targets salicylic acid (SA)-responsive gene PR1 and jasmonic acid (JA)-responsive gene THI2.1. Involved in response to dehydration stress-response in both abscisic acid (ABA)-dependent and ABA-independent pathways; this includes specific genes (e.g. COR15A, ADH1, CBF4, RD29A, RD29B, RD26, ABF3, NCED3 and ABA3) epigenetic regulation (e.g. H3K4me3 and Pol II recruitment) to promotes their transcription and influence ABA production. Implicated in stomatal closure regulation. Indirect repressor of XTH genes (XTH33). Necessary for the phosphorylation of Pol II NRPB1 (e.g. Ser5P and Ser2P) at the promoters of target genes, thus regulating both early and late stages of transcription. Controls root growth and architecture by regulating the timing of root development, stem cell niche maintenance (e.g. quiescent center (QC)), and cell patterning during primary and lateral root development. Modulates cell cycle duration, cell production, and the transition from cell proliferation in the root apical meristem (RAM) to cell elongation.; Trimethylates A4/EF1A post-translationally at Lys-396. Required for actin cytoskeleton organization.
