Populus euphratica JRL Mediates ABA Response, Ionic and ROS Homeostasis in Arabidopsis under Salt Stress

Sodium chloride (NaCl) induced expression of a jacalin-related mannose-binding lectin (JRL) gene in leaves, roots, and callus cultures of Populus euphratica (salt-resistant poplar). To explore the mechanism of the PeJRL in salinity tolerance, the full length of PeJRL was cloned from P. euphratica and was transformed into Arabidopsis. PeJRL was localized to the cytoplasm in mesophyll cells. Overexpression of PeJRL in Arabidopsis significantly improved the salt tolerance of transgenic plants, in terms of seed germination, root growth, and electrolyte leakage during seedling establishment. Under NaCl stress, transgenic plants retained K⁺ and limited the accumulation of Na⁺. PeJRL-transgenic lines increased Na⁺ extrusion, which was associated with the upward regulation of SOS1, AHA1, and AHA2 genes encoding plasma membrane Na⁺/proton (H⁺) antiporter and H⁺-pumps. The activated H⁺-ATPases in PeJRL-overexpressed plants restricted the channel-mediated loss of K⁺ that was activated by NaCl-induced depolarization. Under salt stress, PeJRL⁻transgenic Arabidopsis maintained reactive oxygen species (ROS) homeostasis by activating the antioxidant enzymes and reducing the production of O₂^- through downregulation of NADPH oxidases. Of note, the PeJRL-transgenic Arabidopsis repressed abscisic acid (ABA) biosynthesis, thus reducing the ABA-elicited ROS production and the oxidative damage during the period of salt stress. A schematic model was proposed to show the mediation of PeJRL on ABA response, and ionic and ROS homeostasis under NaCl stress.