Although high mobility group B (HMGB) proteins have been identified from a variety of plant species,their importance and functional roles in plant responses to changing environmental conditions are largely unknown. Here,we investigated the functional roles of a CsHMGB isolated from cucumber (Cucumis sativus L.) in plant responses to environmental stimuli. Under normal growth conditions or when subjected to cold stress,no differences in plant growth were found between the wild-type and transgenic Arabidopsis thaliana overexpressing CsHMGB. By contrast,the transgenic Arabidopsis plants displayed retarded germination compared with the wild-type plants when grown under high salt or dehydration stress conditions. Germination of the transgenic plants was delayed by the addition of abscisic acid (ABA),implying that CsHMGB affects germination through an ABA-dependent way. The expression of CsHMGB had affected only the germination stage,and CsHMGB did not affect the seedling growth of the transgenic plants under the stress conditions. The transcript levels of several germination-responsive genes were modulated by the expression of CsHMGB in Arabidopsis. Taken together,these results suggest that ectopic expression of a CsHMGB in Arabidopsis modulates the expression of several germination-responsive genes,and thereby affects the germination of Arabidopsis plants under different stress conditions. Although high mobility group B (HMGB) proteins have been identified from a variety of plant species, their importance and functional roles in plant responses to changing environmental conditions are are unknown. Here, we investigated the functional roles of a CsHMGB isolated from cucumber (Cucumis Under normal growth conditions or when subjected to cold stress, no differences in plant growth were found between the wild-type and transgenic Arabidopsis thaliana overexpressing CsHMGB. By contrast, the transgenic Arabidopsis plants displayed retarded germination compared with the wild-type plants when grown under high salt or dehydration stress conditions. Germination of the transgenic plants was delayed by the addition of abscisic acid (ABA), implying that CsHMGB affects germination through an ABA-dependent way. CsHMGB had affected only the germination stage, and CsHMGB did not affect the seedling growth of the trans genic plants under the stress conditions. The transcript levels of several germination-responsive genes were modulated by the expression of CsHMGB in Arabidopsis. Taken together, these results suggest that ectopic expression of a CsHMGB in Arabidopsis modulates the expression of several germination-responsive genes, and so affects the germination of Arabidopsis plants under different stress conditions.