Xyloglucan acetyltransferase that catalyzes the acetylation of fucosylated Gal residues on xyloglucan side chains (PubMed:30083810). Predominantly catalyze 6-O-monoacetylation of Gal residues in the Fuc-Gal-Xyl trisaccharide side chains of xyloglucan oligomers (PubMed:30083810). Involved in xyloglucan specific O-acetylation in roots and rosette leaves (PubMed:22086088). No visible phenotype. Loss of O-acetylated xyloglucan oligosaccharides in roots and rosette leaves, but no effect on xyloglucan O-acetylation in seeds. Contains 2 motifs that are conserved in esterases, but it is unlikely that this protein belongs to the catalytically active pectin esterases. A naturally occurring ecotype (cv. Ty-0) lacks AXY4-mediated xyloglucan O-acetylation due to 2 amino acid changes, Asp367Glu and Gly368Lys (PubMed:22086088). Belongs to the PC-esterase family. TBL subfamily.