Auxin is involved in NtIAA17-mediated regulation of root development under salt stress in tobacco.

NtIAA17 acts as a positive regulator of salt tolerance in tobacco, which alleviates salt-repressed root growth by sustaining auxin homeostasis and antioxidant capacity. Across the globe, soil salinization severely restricts plant growth and crop yield, posing a serious threat to agricultural sustainability. While auxin is indispensable for the control of root development and abiotic stress adaptation, the precise mechanism through which this hormone modulates salt tolerance in tobacco remains poorly understood. Here, we demonstrate that salt stress markedly inhibits root growth in tobacco, while exogenous auxin application effectively alleviated this inhibitory effect. Transcriptome analysis revealed that salt stress extensively reprogrammed the genes associated with auxin synthesis, polar transport, and signal transduction pathways. We further cloned and characterized NtIAA17, a salt‑inducible Aux/IAA gene encoding a nucleus‑localized protein with distinct tissue‑specific expression. CRISPR-Cas9-mediated knockout of NtIAA17 enhanced salt sensitivity in tobacco. Compared with wild-type plants, the NtIAA17-knockout lines showed reduced auxin accumulation, lower transcript levels of auxin synthesis (NtYUCCAs) and transport (NtPINs) genes, stunted root growth, and compromised antioxidant capacity under salt stress. Collectively, our results demonstrate that NtIAA17 functions as a positive regulator of salt tolerance in tobacco by coordinating auxin signal transduction and antioxidant defense pathways, thus offering a promising genetic target for engineering salt-tolerant crops.