Methylesterase shown to have carboxylesterase activity, methyl indole-3-acetic acid (MeIAA) esterase activity, methyl salicylate (MeSA) esterase activity and methyl jasmonate (MeJA) esterase activity in vitro. Required to convert methyl salicylate (MeSA) to salicylic acid (SA) as part of the signal transduction pathways that activate systemic acquired resistance in systemic tissue. MeSA is believed to be an inactive form that needs to be demethylated to exert a biological effect. H2O + methyl (indol-3-yl)acetate = (indol-3-yl)acetate + H(+) + methanol H2O + methyl (-)-jasmonate = H(+) + jasmonate + methanol H2O + methyl salicylate = H(+) + methanol + salicylate Esterase activity is down-regulated by salicylic acid (SA). Plant hormone biosynthesis. Lipid metabolism; oxylipin biosynthesis. By pathogen infection. Expression of MES9 can restore systemic acquired resistance in SAR-deficient tobacco plants. Belongs to the AB hydrolase superfamily. Methylesterase family.