Promoter characterization of chickpea delta-1-pyrroline-5- carboxylate synthetase (P5CS) gene provides novel insights into its stress responsiveness

Proline is an osmolyte that accumulates in response to various environmental stresses and serves several protective functions in plants. The gene P5CS (delta-1-pyrroline-5-carboxylate synthetase) codes a key regulatory enzyme for proline biosynthesis. In the present study, the promoter region of the chickpea P5CS gene (CaP5CS) was isolated and in-silico characterized. The expression of the gene was examined under various abiotic stresses, such as cold, salinity and dehydration and also on the application of various phytohormones and chemicals to understand the changes in gene expression which are driven by the promoter. Structurally, the promoter sequence was enriched in many cis-regulatory elements (CREs) recognized by transcription factors (TFs) involved in both ABA (Abscisic acid)-dependent and independent signaling pathways for proline biosynthesis. The gene was observed to be both spatially and temporally regulated. It was observed that the gene was highly up-regulated under heat and dehydration stress at 3 hours of stress treatment. Under dehydration, for the same tissues, the proline content was also estimated to increase by more than 3-fold from 3 to 6 hrs. Notably, under cold and IAA (indole-3-acetic acid) treatment, the gene was down-regulated, which confirms the role of the gene primarily under osmotic stress. This study provides novel insights into the regulation of proline biosynthesis in chickpea. Also, the promoter isolated can be utilized to enable spatial and temporal control in transgene expression in genetically modified crops developed for enhanced stress tolerance.