Catalyzes xyloglucan endotransglycosylation (XET). Cleaves and religates xyloglucan polymers. Does not catalyze xyloglucan endohydrolysis (XEH) (PubMed:25849978). Overexpression in Arabidopsis transgenic plants results in elevated tolerance to abiotic stress, such as salt, ABA (abscisic acid) and drought stresses, and in the production of wider leaves. Overexpression in transgenic tomato plants slows down fruit ripening and softening, and the plants produce larger fruits. Both transgenic plants have larger and more irregular cells. Moreover, the fruits of the transgenic tomato have higher density of cell wall and intercellular spaces. May provide cells with more strength and thickness to maintain structural integrity (PubMed:28155115). Probably involved in cell wall assembly and synthesis in fast growing tissues and in the maintenance of firmness in mature fruits (PubMed:25849978, PubMed:28155115). breaks a beta-(1->4) bond in the backbone of a xyloglucan and transfers the xyloglucanyl segment on to O-4 of the non-reducing terminal glucose residue of an acceptor, which can be a xyloglucan or an oligosaccharide of xyloglucan. Optimum pH is between 5-5.5. Loses activity rapidly when pH is lowered from 5 to 4. Expressed in fruit pulp (PubMed:23265513, PubMed:25849978). Expressed in leaves, flowers, calyces, stems and fruits. Highest expression in leaves and lowest in fruits (PubMed:28155115). Expressed during fruit ripening (PubMed:23265513, PubMed:25849978, PubMed:28155115). During storage, highest expression is on day 3, decreasing until day 12 where expression increases again, but after which it decreases sharply until end of storage (day 18) (PubMed:23265513). Expression is very high in immature growing fruits, with the highest expression 100 days after full bloom, after which expressed at low levels during the mature stage (PubMed:25849978, PubMed:28155115). Expression in fruits during storage at 25 degrees Celsius is lower than the expression at the time of harvest (PubMed:25849978). Expression in young leaves is significantly higher than in mature leaves (PubMed:28155115). In fruits, expression is decreased by gibberellic acid (GA3) or 1-methylcyclopropene (1-MCP) at the beginning of storage (until day 6) (PubMed:23265513). Expression in harvested fruits is increased by low (0 degrees Celsius) temperature treatment, particularly at the end of storage (day 32) (PubMed:25849978). Contains at least one intrachain disulfide bond essential for its enzymatic activity. Belongs to the glycosyl hydrolase 16 family. XTH group 2 subfamily.