Regulation of proline transporters in salt stress response in plants

Abstract

Abstract Among the environmental stresses, salt stress is considered the most important one, which unfavorably affects the physiobiochemical process of plants. Under salinity conditions, the growth and development of plants are hampered in two ways: (i) osmotic stress increases the concentration of phytotoxic ions in the plant cells, which causes ion imbalance in the cytosol, and (ii) oxidative stress as a consequence of the excessive production of reactive oxygen species (ROS). However, salt-tolerant plants and halophytes can acclimatize to the salt-induced oxidative stresses through biosynthesis and transportation of osmotically active compounds, such as sugars, proline (Pro), and betaine. Among them, accretion of Pro in the cells of the plant could improve the adaptation ability of plants against salt stress through maintaining the integrity of membrane of the cells and limiting the excess production of ROS, thus acting as a compatible solute during environmental stress as well as redox-buffering and energy transfer. Pro transporters, including both families of amino acid–polyamine–choline (APC) and amino acid-transporter (ATF)/amino acid/auxin permease (AAAP) including several subfamilies of lysine/histidine transporters (LHTs), the amino acid permease (AAPs), and proline transporters (ProT), act in great roles to enhance the survival ability of plants against salt stress. Similarly, major candidate genes in transgenic plants also have a positive effect to enhance the level of Pro in plant cells to mitigate the adverse effect of salinity stress. Therefore, it is confirmed that enhancement and transportation of Pro in plants’ organs are important survival strategies against salt stress. This review summarizes and discusses novel perceptions into the roles of ProT for improving plant tolerance against salt stres