DNA binding of citrus dehydrin promoted by zinc ion

Dehydrins are hydrophilic proteins that accumulate during embryogenesis and osmotic stress responses in plants. Here, we report an interaction between citrus dehydrin Citrus unshiu cold-regulated 15 kDa protein (CuCOR15) and DNA. Binding of CuCOR15 to DNA was detected by an electrophoretic mobility shift assay, a filter-binding assay and Southwestern blotting. The binding was stimulated by physiological concentrations of Zn(2+), but little stimulation occurred when other divalent cations, such as Mg(2+), Ca(2+), Mn(2+), Ni(2+) and Cu(2+), were substituted for Zn(2+). Ethylenediaminetetraacetic acid cancelled the Zn(2+)-stimulated binding. A binding curve and competitor experiments suggested that the DNA binding of CuCOR15 exhibited low affinity and non-specificity. Moreover, tRNA competed with the DNA binding. Histidine-rich domains and a polylysine segment-containing domain participated in the DNA binding. These results suggest that CuCOR15 can interact with DNA, and also RNA, in the presence of Zn(2+). Dehydrin may protect nucleic acids in plant cells during seed maturation and stress responses.