BOUNDARY OF ROP DOMAIN3 Modulates Salt Tolerance by Mediating Cuticle Wax Synthesis

Soil salinity largely impacts plant growth and development worldwide. Uncovering important regulators involved in plant salt tolerance is crucial for helping plants survive in saline land through genetic engineering. Nonetheless, potential key genes directly related to tolerance to soil salinity have not been fully identified. Through a soil-based genetic screen, we obtained the salinity-tolerant mutant tos1 (tolerance of salt 1), which exhibited glossier and greener leaf morphology under salt stress. tos1 mutation localized at the functionally uncharacterized gene BOUNDARY OF ROP DOMAIN3 (BDR3). A defect in BDR3 results in enhanced resistance to salt stress, accompanied by lower Na⁺ accumulation and water deprivation mediated by a decreased transpiration rate, due to the increased accumulation of cuticular wax, especially VLCFAs and alkanes. BDR3 has no lipase activity, but the fatty acid metabolic process was strongly affected, and glycerolipid hydrolysis was enhanced in tos1; more fatty acids were consumed for wax synthesis, strengthening the cuticular wax maintenance. Our results demonstrate that BDR3 is a novel and negative regulator involved in plant salt tolerance, controlling cuticular transpiration and ion balance depending on its biofunctions in wax synthesis through fatty acid metabolic reprogramming. The study could provide a new molecular basis for the improvement of the regulatory network of wax biosynthesis and plant salt tolerance.