Isolation and characterization of a Δ¹-pyrroline-5-carboxylate synthetase (NtP5CS) from 'Nitraria tangutorum' Bobr. and functional comparison with its 'Arabidopsis' homologue

Several functional and regulatory proteins play important roles in controlling plant stress tolerance. Proline (Pro) is one of the most accumulated osmolytes correlated with tolerance to stresses. Δ¹-Pyrroline-5-carboxylate synthetase (P5CS) is a rate-limiting enzyme in Pro biosynthesis. In the present study, we isolated the cDNA for a P5CS gene ('NtP5CS') from the halophyte 'Nitraria tangutorum'. Phylogenetic analysis and subcellular localization analysis of NtP5CS-GFP protein in onion cells showed that 'NtP5CS' was a new 'P5CS' gene and was involved in Pro synthesis in 'N. tangutorum'. Expression of the 'NtP5CS' gene was induced by salt stress, dehydration, and high and low temperatures. 'Escherichia coli' overexpressing 'AtP5CS' or 'NtP5CS' exhibited better growth in all treatments, including high salinity, high alkalinity, dehydration, osmotic, heat and cold stresses. Additionally, 'NtP5CS' recombinant 'E. coli' cells grew better than did 'AtP5CS' recombinant cells in response to abiotic stresses. Our data demonstrate that the 'P5CS' from a halophytic species functions more efficiently than its homologue from a glycophytic species in improving the stress tolerance of 'E. coli'.