A Lycium chinense-derived P5CS-like gene is regulated by water deficit-induced endogenous abscisic acid and overexpression of this gene enhances tolerance to water deficit stress in Arabidopsis

Proline is one of the most common compatible osmolytes in water-stressed plants. Delta(1)-Pyrroline-5-carboxylate synthetase (P5CS) catalyzes the rate-limiting step of proline synthesis in plants. Abscisic acid (ABA) is an important plant hormone, and plays a critical role in triggering plant responses to different stresses such as water deficit. The interplays between P5CS transcript levels, endogenous ABA and proline content under long-term water deficit stress in halophyte plants have yet to be identified. In this study, a novel P5CS gene was isolated from leaves of Lycium chinense and characterized as a stress-induced type of P5CS gene, designated LcP5CS. The function of LcP5CS was confirmed in vitro with an Escherichia coli expression system. The correlation between LcP5CS transcript expression, proline accumulation and water deficit-induced endogenous ABA accumulation was explored using a potent ABA inhibitor, abamine SG. To characterize the cis elements responsible for this correlated regulation, the LcP5CS promoter was isolated and transcriptionally fused to a beta-glucuronidase (GUS) coding region, then transformed into Arabidopsis. The T2 generation of transformants was analyzed by histochemical GUS assay. Strong staining was observed in the leaves of plants treated with water deficit stress and the staining was reduced by co-treatment with abamine SG. The involvement of endogenous ABA in modulating the LcP5CS transcript levels was confirmed in transgenic Arabidopsis expressing ProLcP5CS::LcP5CS which was grown under water deficit stress. The transgenic Arabidopsis expressing ProLcP5CS::LcP5CS also showed great tolerance to water deficit stress.