The olive plant microbiome: Regional variations, climate change resilience and cultivar-specific dynamics in arid and Mediterranean regions

Drought, heat, salinity and pathogens are emerging issues that continuously threaten olive cultivation in arid and Mediterranean environments, making it essential to understand the functional roles of the microbiomes associated with olives in enhancing the resilience of the plants. This review summarizes existing information on the taxonomic structure and functional characteristics of microbial communities in the rhizosphere, root and shoot endosphere, phyllosphere and xylem. The main microbial activity, such as ACC deaminase activity, exopolysaccharide synthesis, osmolyte synthesis, siderophore-mediated nutrient uptake and antioxidant induction, has been found to enhance the olive water-use efficiency (12-28%), increase root elongation (30%), phosphorus uptake (45%) and reduce the indicators of oxidative stress (40-60%) in harsh climatic conditions. In spite of these advantages, there are still large research gaps, such as the use of taxonomic profiling, small-scale functional characterization, patchy sampling patterns and geographic bias of Mediterranean systems. The dynamic interactions between genotype, environment, and management, as well as the assembly of microbes, are still poorly understood, as is the contribution of rare and specialist taxa and endophytic communities to resistance against vascular pathogens. We will discuss these limitations by highlighting the necessity of integrated multi-omics research, longitudinal research, and controlled experiments of genotype-environment and investigation of regions where olive is poorly represented. Synthetic microbial communities, cultivar-specific microbial recruitment, restoring soil health and microbiome-informed breeding are also assessed in this review as climate resilient. A conceptual framework is suggested to connect mechanistic knowledge to translational applications, including microbial inoculants, precision agronomy and system-level management in a conceptual framework named Way Forward. Collectively, this review provides a mechanistic, holistic perspective on the olive holobiont and outlines actionable pathways for sustainable, climate-adaptive olive production.