Indexing heat stress induced changes in transgenic tobacco by overexpressing membrane-tethered transcription factor from Sorghum bicolor bZIP17

Basic leucine zipper (bZIP) TF family is key regulator of diverse biological functions, including heat stress tolerance. However, its role in response to heat stress is unexplored in Sorghum bicolor, an abiotic stress-tolerant cereal plant. Bio-prospecting of genes for abiotic stress tolerance from elite natural stress-tolerant species is a promising approach for development of abiotic stress-tolerant crops. Therefore, qRT-PCR analysed for heat stress induced bZIP17 gene from S. bicolor, showed 14.7 and 17.3-fold expression at 4 h and 6 h of heat stress respectively at one-month old seedling stage. Further its cDNA sequence was cloned (named as SbbZIP17) for further functional validation in model plant system. In silico analysis showed SbbZIP17 encodes for bZIP polypeptide, an endoplasmic reticulum (ER) type II membrane-tethered transcription factor (type II MMTF), highly conserved, having a single ligand-binding site, interacting with heat stress-responsive proteins (HSP70, NF-Ys), expressed in different tissues and organs. Over-expression of SbbZIP17 in independent events of transgenic tobacco (Nicotiana tabacum) lines (T₁) is responsible for activation of genes involved in unfolded protein response (UPR) pathway under heat stress. Transgenic tobacco lines showed enhancement in hydration status, antioxidant activity, reduction in chlorophyll loss, and membrane damage. Our analysis demonstrated that SbbZIP17 plays an important role in regulating heat stress tolerance in plants.