Overview of molecular mechanisms underlying stress responses; signaling pathways and secondary metabolite synthesis in plants.

Plants are susceptible to several biotic and abiotic stressors, including pathogens, extreme salinity, temperature, and drought. Continuous exposure to these conditions activates complex molecular mechanisms in plants. These include stress-signaling pathways mediated by phytohormones such as cytokins, salicylic acid, auxins, abscisic acid, jasmonic acid, and ethylene. These signaling molecules further interact with cellular pathways regulating stress-responsive gene expression through transcription factors such as DREBs, MYBs, bZIPs, and NACs. Key cellular pathways include mitogen-activated protein, calcium-dependent protein, and receptor-like kinases. Under continuous stress signaling, plants adopt adaptive strategies, including increased biosynthesis of secondary metabolites that protect against oxidative stress, pathogens, herbivores, and environmental stress. Major secondary metabolites include alkaloids, flavonoids, terpenoids, phenolic acids, and saponins. These molecules modulate redox homeostasis and activate antioxidant defense systems, including superoxide dismutase, catalase, and peroxidase. Advanced genomic and molecular tools reveal complex interactions between secondary metabolite synthesis and stress signaling. This suggests a novel approach to enhancing plant stress tolerance and improving crop resilience through genetic manipulation of these pathways. Given the complexity of these pathways, integrated system biology approaches are highly useful. Therefore, this review aims to explore the molecular mechanisms controlling plant stress regulation and their relationship to secondary metabolite biosynthesis. This review further proposes integrative system-biology approaches to enhance stress tolerance and to produce bioactive compounds for agricultural and pharmaceutical applications.