OsNCED1, a chloroplast ABA biosynthase, regulates multiple abiotic stress tolerance in rice

Abscisic acid (ABA)‌ is one of the most critical stress hormones in plants, yet the mechanisms underlying its biosynthesis pathway in regulating multiple abiotic stress tolerance remain poorly understood. In this study, we identified the function of 9-Cis-Epoxycarotenoid Dioxygenase 1 ‌(OsNCED1)‌, a key ABA biosynthetic enzyme gene in rice (Oryza sativa L.), in regulating multiple abiotic stresses (cold, salt, and osmotic stress) tolerance. OsNCED1 is a chloroplast-localized ABA synthase. Its expression is significantly induced by multiple abiotic stresses. Knockout of ‌OsNCED1‌ markedly impairs the tolerance of rice seedlings to cold, salt, and osmotic stresses, whereas exogenous ABA application restores the stress hypersensitivity of ‌osnced1‌ mutants. Overexpression of ‌OsNCED1‌ significantly enhances tolerance to multiple stresses. Physiological analyses indicate that OsNCED1 mediates stress tolerance through the maintenance of ABA homeostasis and reactive oxygen species (ROS) scavenging‌. The potential molecular mechanism suggests that OsNCED1 alters the expression of ABA signaling pathway genes in mutant and overexpression plants to regulate stress tolerance. Taken together, ‌OsNCED1 is a ‌positive regulator‌ of stress tolerance and represents a promising target gene for improving multiple abiotic stress tolerance in rice seedlings via molecular breeding strategies in the future.