Abscisic acid confers antibiotic stress tolerance in cucumber by alleviating antibiotic phytotoxicity and decreasing the levels of antibiotic and antibiotic resistance genes.

Antibiotic pollution in the environment causes serious threats to crop growth and human health. However, effective strategies for alleviating antibiotic stress based on endogenous signaling response to antibiotics in plants remain unclear. Here, we found that the toxic effects of ciprofloxacin (CIP) and tetracycline (TC) at 1 mg L-1 on cucumber seedlings were stronger than lincomycin hydrochloride, sulfacetamide, thiamphenicol and tylosin. Importantly, both CIP and TC induced abscisic acid (ABA) accumulation and the transcripts of ABA-related genes. In turn, spraying exogenous ABA alleviated antibiotics-induced growth and photosynthesis inhibition and oxidative stress dose-dependently, with the most effective concentration of 20 µM. Moreover, ABA inhibited the activities of V-ATPase and V-PPase associated with antibiotics uptake. Subsequently, ABA effectively decreased the root and shoot accumulation of CIP and TC by 41.3 % and 58.0 %, 62.8 % and 85.4 %, respectively, compared with CIP and TC stress. Finally, CIP and TC promoted the accumulation of antibiotic resistance genes (ARGs), while ABA significantly declined the relative abundance of target ARGs (e.g., qnrD, tetG-02 and tetR-02), mobile genetic elements (MGEs) (e.g., cIntI-1(class1) and intI1), and potential host bacteria (e.g., Pseudomonas, Bacillus and Nocardioides) at the genus level. Network analysis and structural equation models displayed that bacterial communities and MGEs were the vital factors influencing the abundances of ARGs. Overall, these findings demonstrated that ABA confered antibiotic stress tolerance in cucumber by alleviating antibiotic phytotoxicity and decreasing the levels of antibiotics and ARGs, providing a novel and effective method for mitigating the antibiotics contamination in the soil-plant system.