Methylates arginine residues of myelin basic protein (MBP) in vitro. Methylates symmetrically histone H4 of the FLC chromatin to form H4R3me2s, which in turn suppresses FLC expression to induce flowering. Regulates alternative splicing by methylating spliceosomal proteins. Involved in the post-transcriptional regulation of the circadian clock. L-arginyl-[protein] + 2 S-adenosyl-L-methionine = 2 H(+) + N(omega),N(omega)-dimethyl-L-arginyl-[protein] + 2 S-adenosyl-L-homocysteine Highly expressed in flowers, roots and siliques, lower expression in stems and mature leaves (at protein level). Abundant in shoot apex, young leaves and leaf primordia, floral and inflorescence meristems, gynoecium, stamens, sepals and young siliques, but not in older leaves, petals and vascular tissues. High levels from 5 to 20 days after germination (at protein level). Circadian-regulation. Plants are late-flowering. Increased alternative splicing of several genes, including APRR9. Belongs to the class I-like SAM-binding methyltransferase superfamily. Protein arginine N-methyltransferase family.