Research advances of salt exclusion, salt sequestration, salt secretion, and salt signaling regulation in plants

Salt stress is one of the main environmental stress factors with increasing negative impacts on agricultural production worldwide, posing serious threats to global food security. It is of great importance to investigate the response strategies and mechanisms of plants to salt stress. This review article comprehensively introduces the research advances of salt exclusion, salt sequestration, salt secretion, and salt signaling regulation in plants. For salt exclusion, plants block the entry of salt into root and reduce the transport of salt to aerial parts by maintaining the integrity of cell wall, enhancing the barrier function of apoplasts, and promoting the ion antagonism. Plants can cope with salt stress through vacuolar sequestration, a key salt sequestration mechanism for ion homeostasis. Plants can secrete salt from cytoplasm to extracellular compartments through salt-overly-sensitive (SOS) pathway and some anion channels and transporters, and from the inside to the outside of plants through salt glands and microhairs. Moreover, signaling regulation, including Ca2+ signaling cascades, phytohormone networks, and reactive oxygen species (ROS) signaling pathways, serves as a key cellular mechanism for plant salt stress mitigation. In addition, some unresolved scientific issues concerning plants response to salt stress are proposed for further studies. This review article provides a theoretical framework for improving crop yield under salt stress conditions.