S-adenosyl-L-methionine (SAM)-dependent methyltransferase (MTase) which mediates the methylesterification of the pectin homogalacturonan (HG) and thus regulates cell wall biosynthesis, at least in suspension-cultured cells. Glycan metabolism; pectin biosynthesis. Highly expressed and abundant in suspension-cultured cells, but low levels in seedlings. In seedlings, no altered phenotypes or changes in pectin methylation (PubMed:21725030). In contrast, suspension-cultured cells exhibit less pectin methylation as well as altered composition and assembly of cell wall polysaccharides (PubMed:21725030). Belongs to the methyltransferase superfamily.