Role of endophytic bacteria in salinity stress amelioration by physiological and molecular mechanisms of defense: A comprehensive review

Climate change is a major concern for sustainable agriculture in the twenty-first century, as it has an impact on crop production and soil fertility, which may increase the risk of famine. Of the array of issues pertaining to climate change, salt stress is one of the most significant factors affecting crop production all over the world. Plants undergo different morphological, physio-chemical, and molecular adaptations to deal with salinity stress. However, several mitigation strategies are also used to cope with the drastic effects of salt stress. Microbial-based solutions, in particular, are highly desirable in sustainable agriculture as they provide a natural, cost-effective, and environmentally safe approach for improving plant growth and yield. Endophytic bacteria not only preserve soil fertility but also boost plant growth under salt stress situations. These bacteria mitigate salt stress by lowering the synthesis of reactive oxygen species (ROS) and facilitating nutrient availability. Moreover, the endophytic bacteria also regulate the expression of genes responsible for producing various phytohormones, antioxidant enzymes, siderophores, volatile organic compounds, and ROS-scavenging enzymes, and other substances. The current research extensively explored the potential pathways involved in plant growth modulation and salinity stress mitigation by endophytic bacteria. Bacterial endophytes as a plant's second genome might be a natural strategy for improving a plant's growth and yield under salt stress conditions.