Overexpression of DHN9 from Pyrus betulifolia Enhances Freezing Stress Tolerance in Broussonetia papyrifera

• PbDHN9 , a novel dehydrin from Pyrus betulifolia , localizes to the endoplasmic reticulum • PbDHN9 expression was significantly upregulated under cold stress conditions • PbDHN9 enhances the cold tolerance of Broussonetia papyrifera by modulating the accumulation of soluble proteins and proline, as well as the activity of antioxidant enzymes The dehydrin (DHN) gene family plays a crucial protective role in plant responses to low-temperature stress. Pyrus betulifolia is a highly cold-tolerant species with superior overwintering ability, making it a suitable material for studying cold-tolerance mechanisms. To clarify the function of DHN genes in woody plants, the PbDHN9 gene from Pyrus betulifolia was cloned and introduced into Broussonetia papyrifera using Agrobacterium-mediated transformation. The cold-induced PbDHN9 encoded a 275-amino-acid hydrophilic protein localized to the endoplasmic reticulum. PbDHN9 expression enhanced cold and freezing tolerance in Broussonetia papyrifera , which was associated with increased soluble protein and proline contents to maintain cellular moisture, and with enhanced superoxide dismutase, peroxidase, and catalase activity to decrease oxidative damage. These findings help clarify the molecular basis of low-temperature tolerance in Pyrus betulifolia and provide a potential gene resource for breeding cold-hardy pear varieties.