EcbZIP60, a basic leucine zipper transcription factor from Eleusine coracana L. improves abiotic stress tolerance in tobacco by activating unfolded protein response pathway

The basic leucine zippers (bZIPs) are one of the largest families of transcription factors that have been demonstrated to play diverse roles in plant growth development. These proteins are known to regulate many cellular responses in plants under stress conditions. In this study, a stress-responsive transcription factor belonging to bZIP family was cloned from finger millet (Eleusine coracana) and functionally validated in tobacco. The expression of EcbZIP60 was highly upregulated under drought, osmotic, salt and methyl viologen-induced stress in finger millet. Constitutive expression of EcbZIP60 in tobacco resulted in reduced growth of plants under normal growth conditions. However, the transgenic plants showed improved tolerance to drought stress with higher stomatal conductance and photosynthesis, resulting in improved growth. The transgenic plants also showed increased tolerance to salinity and methyl viologen-induced oxidative stress and to endoplasmic reticulum stress inducers dithiothreitol and tunicamycin. The transgenic plants showed significant upregulation of unfolded protein-responsive pathway genes such as BiP1, CRT1 and PDIL both under normal and stress conditions, although dehydrin group of genes did not show any upregulation. The results demonstrate that improved tolerance of EcbZIP60-expressing transgenic tobacco to diverse stresses could be through unfolded protein-responsive signalling pathway.