A rosemary (Salvia rosmarinus Spenn) extract promotes oxidative stress tolerance in Arabidopsis thaliana

Oxidative stress is a consequence of many abiotic stresses, and developing environmentally friendly, efficientbiostimulant strategies to mitigate stress is of paramount importance to modern agriculture. Here, we report thattreatment of Arabidopsis thaliana with an aqueous rosemary (Salvia rosmarinus Spenn) extract induced toleranceto oxidative stress. Arabidopsis plants were sprayed with either water (control) or aqueous rosemary extract(ARE) and then subjected or not to oxidative stress induced by 30 μM paraquat (PQ). Comprehensive gene expressionswere assessed by RNA sequencing under stress and non-stress conditions. PQ treatment inhibitedphotosynthesis, as evidenced by reductions in maximum PSII quantum yield and the steady-state fluorescencedecline ratio, and caused membrane rupture, as documented by electrolyte leakage. Cell death was manifested asmassive necrotic lesions on the leaves. In contrast, plants that were treated with ARE prior to PQ application(ARE + PQ) showed significantly reduced stress and cell death markers, indicating that ARE protects Arabidopsisfrom PQ-induced oxidative stress. Five reactive oxygen species (ROS) marker genes were upregulated by PQ,confirming oxidative stress at the molecular level. PQ also upregulated heat shock and other abiotic stress-relatedgenes, as well as genes from the ethylene and senescence pathways, while genes related to auxin, growth, andphotosynthesis were repressed. The ARE treatment prior to the PQ application reversed these changes.Furthermore, ARE alone upregulated auxin- and photosynthesis-related genes and downregulated most chlorophyllcatabolism genes. Collectively, our findings identify rosemary as a promising biostimulant that protectsArabidopsis from oxidative stress and highlight the underlying molecular mechanisms.