Abiotic stress and ABA-inducible Group 4 LEA from Brassica napus plays a key role in salt and drought tolerance

Late-embryogenesis abundant (LEA) proteins are a family of hydrophilic proteins that form an integral part of desiccation tolerance of seeds. LEA proteins have been also postulated to play a protective role under different abiotic stresses. Their role in abiotic stress tolerance has been well documented for Group 1, 2 and 3 LEAs among the nine different groups. The present study evaluates the functional role of a Group 4 LEA protein, LEA4-1 from Brassica napus. Expression analysis revealed that abscisic acid, salt, cold and osmotic stresses induce expression of LEA4-1 gene in leaf tissues in Brassica species. Conversely, reproductive tissues such as flowers and developing seeds showed constitutive expression of LEA4, which was up-regulated in flowers under salt stress. For functional evaluation of LEA4-1 with regard to stress tolerance, LEA4-1 cDNA was cloned from B. napus, and overexpressed in both Escherichia coli and transgenic Arabidopsis plants. Overexpression of BnLEA4-1 cDNA in E. coli conferred salt and extreme temperature tolerance to the transformed cells. Furthermore, transgenic Arabidopsis plants overexpressing BnLEA4-1 either under constitutive CaMV35S or abiotic stress inducible RD29A promoter showed enhanced tolerance to salt and drought stresses. These results demonstrate that LEA4-1 plays a crucial role in abiotic stress tolerance during vegetative stage of plant development.