Dehydrin proteins are known to serve a wide variety of intracellular protective functions and enhance the capability of plants to deal with abiotic stresses. The gene for a SK 5 type dehydrin from the arctic chickweed plant Cerastium arcticum (CarDHN) was introduced into tobacco plants. Stress responses of the transgenic plants were evaluated. Compared to the untransformed wild type plants, the CarDHN-expressing plants exhibited improved tolerance to salt and osmotic stress during seed germination and seedling growth, and survived in -10°C freezing treatment. These CarDHN plants also accumulated lower levels of free proline under salt stress and exhibited lower transcription levels of HSP70 and HSP26 under drought or salt stress, suggesting a possible pleiotropic effect of CarDHN on stress response at cellular or molecular level. However, no significant phenotypic differences were observed between the wild type and the CarDHN-expressing plants under drought stress. Our study demonstrated the specific role of the arctic chickweed dehydrin in tolerance to salt, osmotic and freezing stress.
During the course of evolution, organisms have developed genetic mechanisms in response to various environmental stresses including wounding from mechanical damage or herbivory-caused injury. A previous study of wounding response in the plant tobacco identified a unique wound-induced gene, aptly named KED due to its coding for a protein that has an unusually high content of amino acids lysine (K), glutamic acid (E) and aspartic acid (D). However, by far little is known about this intriguing gene. In this study, we investigated the evolutionary aspects of the KED-rich coding genes. We found that a consistent pattern of wound-induced KED gene expression is maintained across representative species of angiosperm and gymnosperm. KED genes can be identified in species from all groups of land plants (Embryophyta). All the KED proteins from vascular plants (Tracheophyta) including angiosperm, gymnosperm, fern and lycophyte share a conserved 19-amino acid domain near the C-terminus, whereas bryophytes (moss, liverwort and hornwort) possess KED-rich, multi-direct-repeat sequences that are distinct from the vascular plant KEDs. We detected KED-rich sequences in Charophyta species but not in Chlorophyta wherever genome sequences are available. Our studies suggest diverse and complex evolution pathways for land plant KED genes. Vascular plant KEDs exhibit high evolutionary conservation, implicating their shared function in response to wounding stress. The extraordinary enrichment of amino acids K, E and D in these groups of distinct and widely distributed proteins may reflect the structural and functional requirement for these three residues during some 600 million years of land plant evolution.
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