OsAAI1 is dependent on the nitrate pathway toregulate rice root development in response to high salt stress

• OsAAI1 is salt-sensitive, inhibited by NaCl but promoted by nitrate. • Salt tolerance and ROS scavenging enzyme activity of OsAAI1 were enhanced by nitrate. • Root scanning provided more insight into root growth and development. • osaai1 was more resistant to salt stress compared to OE 19. • High concentration of nitrate reduced salt damage to OE 19. • OsAAI1 plays a key role in rice salt stress response through the nitrate pathway. Salt stress limits plant growth and yield. Though nitrogen fertilizer can alleviate salt damage, the effects of salt and nitrate on the stress resistance gene OsAAI1 are unclear. This study examined the Salt stress sensitivity of OsAAI1 transgenic lines and nitrate's role. Results showed OsAAI1 expression decreased with Salt and increased with nitrate. Under salt stress, the mutant OsAAI1 ( osaai1 ) had significantly higher plant height, root length and number, and lower ROS accumulation than ZH 11, while OsAAI1 overexpression (OE 19) showed opposite trends. OE 19 also had lower antioxidant enzyme activities and higher MDA content. Analyses of topology, biomass distribution and connectivity of root scans after 30 and 50 days of salt stress treatment showed that osaai1 was able to sustain root growth and development under salt stress conditions, whereas OE 19 was more damaged. Exogenous salt stress tests confirmed these findings. Notably, nitrate application enhanced OsAAI1 is salt tolerance, improving root growth and increasing ROS scavenging enzyme activities. Under KNO₃ induction, high-concentration KNO₃ restores the root phenotype in OE 19. In conclusion, overexpression of OsAAI1 was more sensitive to salt, and OsAAI1 regulated ROS homeostasis through the nitrate pathway to enhance its tolerance to salt stress.