Abiotic stress response of transgenic Arabidopsis overexpressing Brassica napus group 1 LEA genes.

Abstract

Group 1 late embryogenesis-abundant (LEA) proteins are highly hydrophilic group of proteins with a characteristic internal 20-mer amino acid sequence. In Arabidopsis, group 1 LEA (AtEm1 and AtEm6) are expressed at very high levels in seeds during maturation phase, and are necessary for desiccation tolerance of seeds. These genes are also induced by stress hormone ABA in seedlings during early seedling establishment phase. Since these LEA proteins are stored in seeds and also accumulate during seedling establishment, they may impart desiccation tolerance to the germinating seedlings. To examine whether these proteins play a role during seedling establishment under stress conditions, we cloned group 1 LEA genes namely BnEm6 and BnEm1 from Brassica napus and overexpressed in Arabidopsis plants. BnEm6 and BnEM1 LEA proteins possess one and four tandem repeats of “20-mer conserved sequence motif”, respectively. A semi-quantitative RT-PCR analysis showed that these genes are expressed in seeds. Abiotic stress tolerance of transgenic Arabidopsis overexpressing BnEm1 and Em6 under constitutive CaMV35S promoter were evaluated during germination and seedling establishment. These transgenic plants showed significantly higher total root length and surface area as compared to wildtype plants under 200 mM mannitol stress. Under salt stress also, root length was higher in transgenic plants as compared to wild-type plants. These results suggest that LEA1 proteins may probably play a role in root growth under osmotic stresses during seedling establishment.