Proline accumulation and osmotic stress: an overview of P5CS gene in plants

Under osmotic stresses, proline accumulation is an important response of plants to these conditions. Proline is a compatible osmolyte which affects many cellular and molecular aspects of plant in both normal and stressful situations. Proline is shown to be involved in plant development in normal condition and in conferring resistance to plant under biotic and abiotic stresses. Therefore, many surveys have already been designed to unveil its mechanisms and signaling pathway, so that it might be an insight into resolving growing challenge of agriculture, drought and soil salinity. Δ1-pyrroline-5-carboxylate synthetase (P5CS), one of two main enzymes in proline biosynthesis pathway from glutamate precursor, has been demonstrated to play significant role in proline accumulation in plants under water stresses. Regarding the role of P5CS under osmotic stress, there are controversial observations in various plants, hence making it still unknown, whether P5CS is rate-limiting enzyme in the pathway or not. Obviously, transgene P5CS is proved to give higher resistance to transgenic plants under drought and salinity, by elevating proline content. In this literature, proline and its identified various functions in plants, characteristics of P5CS enzyme, signals, inducers and inhibitors of P5CS gene, expression pattern of P5CS under differential conditions in studied plant species are discussed. Finally, we have reviewed generated transgenic plants overexpressing P5CS and consequences of these transformations.