Characterization of transgenic Arabidopsis plants overexpressing GR-RBP4 under high salinity, dehydration, or cold stress.

A glycine-rich RNA-binding protein4 (GR-RBP4), one of the eight GR-RBP family members in Arabidopsis thaliana, was investigated for its stress-related expression, nucleic acid-binding property, and functional roles in plants subjected to various stresses including cold, high salinity, and dehydration. Real-time RT-PCR and GUS expression analyses showed that GR-RBP4 was abundantly expressed in young plants, root tips, and flowers, but weakly in mature leaves and stems, implying that GR-RBP4 is highly expressed in actively proliferating organs. The transcript level of GR-RBP4 increased markedly with cold stress, decreased significantly with salt stress, and decreased slightly with dehydration stress. In vitro nucleic acid-binding assays revealed that GR-RBP4 protein binds sequence non-specifically to RNAs and DNAs. Characterization of the transgenic Arabidopsis plants overexpressing GR-RBP4 under the control of the 35S promoter revealed that 35S::GR-RBP4 lines displayed retarded germination compared with the wild type under salt or dehydration stress. Despite the marked up-regulation of GR-RBP4 expression by cold stress, the 35S::GR-RBP4 lines did not show any noticeable changes in cold or freezing tolerance compared with wild-type plants. These results indicate that GR-RBP4 contributes differently to altered germination and seedling growth of Arabidopsis plants under various stress conditions.