XTHs

XTHs, or xyloglucan endotransglucosylase/hydrolases, are a family of plant enzymes that participate in remodeling the cell wall. Belonging to glycoside hydrolase family 16, they catalyze either transglycosylation, the cleavage of xyloglucan chains followed by reattachment to another xyloglucan molecule, or, in some cases, hydrolysis of the chain. This enzymatic activity enables loosening and restructuring of the primary cell wall during growth and development.

Most XTHs are secreted proteins containing an N-terminal signal peptide that directs them to the apoplast. They possess conserved catalytic motifs characteristic of GH16 enzymes, including a DEIDFEFLG-like motif involved in catalysis. Their activity is modulated by factors such as pH, calcium, and substrate availability.

XTH gene families are large in many plant species, often expanding through gene duplication. Expression is developmentally regulated and responsive to hormones such as auxin and ethylene, as well as to abiotic and biotic stress. XTHs participate in cell elongation in growing tissues, wood formation, fruit softening, pollen tube growth, and wound response, among other processes.

Research on XTHs includes transcriptomic analyses to profile expression, enzymatic assays for XET/XEH activity, and structural studies to identify conserved motifs. Functional investigations using overexpression or genome editing reveal roles in growth, development, and stress adaptation.