Probable O-acetyltransferase involved in the acetylation of xylan during secondary wall biosynthesis. Expressed in cells undergoing secondary wall thickeningin a SND1-dependent manner, such as xylem cells and interfascicular fibers. Mostly expressed in the middle and bottom parts of the inflorescence stems (PubMed:21673009). Mainly observed in the more mature parts of inflorescence stems, but present ubiquitously (PubMed:21212300). No visible phenotype on cell wall acetylation in single mutant (PubMed:21212300). Severe growth phenotypes (e.g. dwarf and abnormal flower organs) associated with reduction in the secondary wall thickening and the stem mechanical strength in the quadruple mutant rwa1 rwa2 rwa3 rwa4 and characterized by reduced xylan acetylation and altered ratio of non-methylated to methylated glucuronic acid side chains. Absence of interfascicular fibers and xylem cells differentiation (PubMed:21673009, PubMed:24019426). The double mutant rwa2 rwa4 and triple mutants rwa2 rwa3 rwa4, rwa1 rwa3 rwa4 and rwa1 rwa2 rwa4 are also dwarfs with abnormal morphology. Altered O-acetylated xyloglucans (XyG) oligosaccharides (XyGOs) composition (PubMed:24019426). Belongs to the PC-esterase family. CASD1 subfamily.