Coffee endophytes: diversity, ecological functions, and application prospects in sustainable production.

Coffee production is increasingly constrained by climatic variability, unstable yields, major pests and diseases, and growing demand for consistent bean quality. Endophytic microorganisms that colonize internal coffee tissues may contribute to plant growth, stress tolerance, disease and pest suppression, and postharvest quality-related processes. However, current knowledge remains fragmented because confirmed endophytes, rhizosphere microorganisms, phyllosphere taxa, and fermentation-associated microbiota are often discussed together. This review synthesizes coffee endophyte diversity, tissue-specific distribution, colonization routes, host-selection filters, ecological functions, and application prospects, while explicitly separating direct endophyte evidence from coffee-associated and indirect evidence. We show that coffee endophytes are shaped by host genotype, tissue niche, altitude, shade, management system, developmental stage, and microbial source pools, rather than representing a fixed list of ubiquitous taxa. Mechanistically, coffee endophytes may influence nutrient acquisition, phytohormone balance, stress physiology, salicylic acid- and jasmonic acid/ethylene-mediated defense signaling, reactive oxygen species regulation, PR proteins, lignification, antimicrobial metabolites, and multitrophic plant-microbe-insect interactions. Current evidence is strongest for isolation, community description, in vitro screening, and short-term greenhouse or pot studies, whereas field persistence, functional stability, biosafety, and formulation remain insufficiently validated. We propose an application-oriented pipeline linking tissue-specific isolation, evidence-level classification, host reinoculation, colonization tracking, multi-omics, synthetic consortia, multi-environment trials, and product development. This synthesis clarifies how coffee endophyte research can move from descriptive microbiome inventories towards reliable microbial tools for sustainable coffee cultivation, integrated pest and disease management, and quality-oriented processing.