Exploiting endophytes to enhance aromatic and medicinal plant resistance to drought and salinity through the modulation of secondary metabolites and defense mechanisms

Abstract Background Aromatic and medicinal plants (AMPs) are more vulnerable to abiotic stresses such as drought and salinity, which contribute to a variety of biochemical, morphological, molecular, and physiological changes that impair plant growth and productivity. The use of symbiotic microorganisms is an approach to minimize the adverse effects of abiotic stressors on agriculture. Recently, interest in endophytic fungi and bacteria has grown because of the many benefits they provide to the host plant while reducing the use of chemicals in agriculture that benefit the environment and human health. The aim of this review is to summarize research on the use of bacterial and fungal endophytes to assist AMPs in combating drought and salinity, primarily through the modulation of secondary metabolites and defense mechanisms. Methods A comprehensive literature review was conducted using the main scientific databases, including PubMed, ScienceDirect, Google Scholar, Scopus, and Web of Science, covering studies published between 2000 and 2025. The selection focused on experimental and review articles addressing the interaction between endophytic microorganisms and AMPs under abiotic stress. The data was analysed thematically to identify mechanisms of tolerance, plant-microbe interactions, and modulation of metabolic pathways. Results Endophytes have proven their ability to protect plants, such as Thymus vulgaris L., Rosmarinus officinalis L., Mentha piperita L., and other plants, from abiotic stresses by directly or indirectly improving their immunity. Additionally, they enhance photosynthesis, improve plant growth, aid in nutrient mineralization, activation of antioxidant enzymes and produce bioactive compounds, hormones, enzymes, and volatile compounds, all of which improve plant productivity and stress resistance. Conclusions Endophytic microorganisms represent a promising and eco-friendly strategy to enhance the resilience of AMPs against drought and salinity stress. By activating antioxidant defense systems, stimulating secondary metabolite biosynthesis, and improving physiological functions, these symbionts help plants maintain growth and productivity under adverse conditions. Their multifunctional role highlights their potential as sustainable biotechnological tools to reduce chemical inputs, promote environmental health, and support the development of climate-resilient agriculture. Future research should focus on field validation, molecular mechanisms, and the formulation of endophyte-based bioinoculants for large-scale agricultural applications.