Analysis of transcriptomic profiles and physiological traits of exogenous 24-epibrassinolide alleviating salt stress in Atractylodes macrocephala Koidz.

Exogenous 24-epibrassinolide (24-epiBL) application is a preferred method for improving salt tolerance in plants. However, information about the effects of exogenous 24-epiBL application related to salt response in Atractylodes macrocephala Koidz. (AMK) has rarely been reported. Here, we aimed to investigate the effects of exogenous 24-epiBL (0.01 mg L⁻¹) on enhancing salt tolerance in AMK seedlings under salt stress (5 g L⁻¹ NaCl) based on seed germination experiments. Our results indicated that NaCl treatment suppresses AMK seed germination, while 24-epiBL treatment under nonstress and stress conditions had positive effects on plant seedling growth. Treatment with NaCl significantly inhibited radicle elongation and root activity to endure salt stress, and 24-epiBL treatment promoted growth and alleviated the damage to osmotic stress, ion stress substances, and oxidative stress by regulating free proline (Pro) and soluble protein (SP) contents and enhancing soluble sugar (SS) conversion. Moreover, the expression of normal development process genes was affected, and differentially expressed genes (DEGs) in multiple pathways associated with amino acid metabolism, signal transduction, carbohydrate metabolism, and lipid metabolism were regulated under NaCl treatment. Further analysis of the AMK transcriptome profile revealed that exogenous 24-epiBL enhanced salt tolerance through hormone regulation and carbohydrate metabolism promotion, salt-responsive gene expression inhibition, and induction of pathways related to terpenoid and polyketide metabolism as well as pentose and glucuronate interconversions for plant growth promotion. Collectively, our findings successfully demonstrate that exogenous 24-epiBL plays a positive role in regulating the AMK response to salt stress, which provides potential genetic resources to improve salt tolerance in plants.