Together with CGR2, required for homogalacturonan pectins (HG) methylesterification in the Golgi apparatus prior to integration into cell walls, essential for general growth and development (PubMed:21422118, PubMed:25704846, PubMed:27208234). Promotes petiole elongation (PubMed:21422118). Impacts photosynthesis and respiration efficiency by influencing leaf mesophyll morphology and physiology; pectin methylesterification modulates both expansion and positioning of cells in leaves, probably by changing cell walls plasticity (PubMed:27208234). Reduced homogalacturonan pectins (HG) methylesterification in cell walls (PubMed:21422118). Plants lacking both CGR2 and CGR3 (cgr2-1 cgr3-1) exihibit severe defects in plant growth and development (e.g. shorter hypocotyl and primary root length due to reduced cell elongation, and abnormal pollen tube elongation), as well as reduced levels of pectin methylesterification associated with decreased microsomal pectin methyltransferase activity. The double mutant cgr2-1 cgr3-1 also lacks uronic acids and methyl ester (PubMed:25704846). Reduced HG methylesterification in cgr2-1 cgr3-1 double mutant results in thin but dense leaf mesophyll that limits CO(2) diffusion to chloroplasts and reduces leaf area, thus impairing photosynthesis efficiency and carbon (C) partitioning (PubMed:27208234). Belongs to the class I-like SAM-binding methyltransferase superfamily.