Acts in the modification of cell walls via demethylesterification of cell wall pectin. [(1->4)-alpha-D-galacturonosyl methyl ester](n) + n H2O = [(1->4)-alpha-D-galacturonosyl](n) + n H(+) + n methanol Glycan metabolism; pectin degradation; 2-dehydro-3-deoxy-D-gluconate from pectin: step 1/5. Expressed in siliques, but not in flower buds. Expression restricted to early to mid-stage of silique development. Not found in vegetative stage. Expressed in the micropyle area of the ovule just after fertilization. The PMEI region may act as an autoinhibitory domain and prevent untimely PME activity during transport. In the N-terminal section; belongs to the PMEI family. In the C-terminal section; belongs to the pectinesterase family.