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 Zn2+, but little stimulation occurred when other divalent cations, such as Mg2+, Ca2+, Mn2+, Ni2+ and Cu2+, were substituted for Zn2+. Ethylenediaminetetraacetic acid cancelled the Zn2+-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 Zn2+. Dehydrin may protect nucleic acids in plant cells during seed maturation and stress responses.

Dehydrins are known as plant stress-responsive genes. Arabidopsis thaliana has 10 dehydrin genes. Among them, one of the highly expressed genes is a KS-type dehydrin (At1g54410). However, the gene product, which is a histidine-rich dehydrin whose molecular mass is 11 kDa (AtHIRD11), has not been studied. Thus, we report the biochemical characterization of the AtHIRD11 protein.Although the AtHIRD11 protein was detected in all organs of Arabidopsis, the bolting stem and the flower showed higher accumulation than the other organs, with the AtHIRD11 protein detected in the cambial zone of the stem vasculature. Most of the AtHIRD11 protein was found to be a bound form. The bound AtHIRD11 was solubilized by 1 M NaCl solution. The extracted AtHIRD11 was retained in immobilized metal-affinity chromatography, and eluted by an imidazole gradient. The native AtHIRD11 prepared from Arabidopsis was partially phosphorylated, but further phosphorylated by casein kinase 2 in vitro. Metal-binding assays indicated that Zn 2? may be the best metal for AtHIRD11 binding. These results suggest that AtHIRD11 is a metal-binding dehydrin that shows a house-keeping expression in Arabidopsis.