Chitinase 38 confers cadmium tolerance via reduced cadmium uptake and metabolic reprogramming in barley

Soil cadmium (Cd) contamination threatens crop productivity and food safety. Chitinase genes (Chit) are well characterized for their roles in plant defense against biotic stresses, but their functions in Cd stress responses remain elusive. Here, we functionally characterize HvChit38, a novel Cd-induced Class I chitinase gene from a Cd-tolerant barley genotype. Chit38 sequences are highly conserved during green plant evolution, with a likely origin from streptophyte algae. HvChit38 overexpression significantly improves plant growth and yield and substantially reduces Cd concentrations in roots, shoots, and grains under Cd stress, whereas HvChit38 silencing results in the opposite phenotypes. Integrated transcriptomic and metabolomic analyses indicate that HvChit38 activates the shikimate pathway mediated by upregulating HvDHQD, which in turn promotes the biosynthesis of downstream phenylpropanoid and terpenoid compounds. This metabolic shift enhances antioxidant capacity and promotes cell wall remodeling with increased lignin and hemicellulose contents and reduced pectin content, thereby restricting Cd uptake and translocation. Virus-induced gene silencing of HvDHQD in HvChit38-overexpressing plants reduced lignin and flavonoid contents while increasing Cd accumulation, confirming that HvChit38 enhances Cd tolerance in barley through HvDHQD upregulation. Collectively, our findings provide the first evidence for a potential link between HvChit38, HvDHQD-mediated shikimate pathway, and Cd tolerance, highlighting HvChit38 as a promising target for breeding Cd-tolerant and low-Cd-accumulation cereal crops.