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). Belongs to the methyltransferase superfamily. Type-7 methyltransferase family.