Catalyzes the methylation of jasmonate into methyljasmonate, a plant volatile that acts as an important cellular regulator mediating diverse developmental processes and defense responses. jasmonate + S-adenosyl-L-methionine = methyl (-)-jasmonate + S-adenosyl-L-homocysteine Binds 1 Mg(2+) ion per subunit. Lipid metabolism; oxylipin biosynthesis. Predominantly cytoplasmic (By similarity). Partially nuclear (By similarity). Expressed in rosettes, cauline leaves and developing flowers but not in young seedlings. By wounding and methyl jasmonate treatment. Belongs to the methyltransferase superfamily. Type-7 methyltransferase family.