Endophytic Fungi in Grasses: Panomics-Driven Mechanisms of Combined Abiotic Stress Tolerance and Climate-Smart Pasture Improvement

Endophytic fungi associated with grasses establish largely asymptomatic relationships that span a mutualism-antagonism continuum shaped by host genotype and environment. Epichloë species (including asexual Neotyphodium forms) are widespread systemic symbionts in cool-season grasses, growing intercellularly, following host development, and often infecting reproductive tissues for vertical transmission by seed. This review synthesizes grass endophyte diversity and biogeography including clavicipitaceous ( Epichloë /Neotyphodium), dark septate endophytes and non-clavicipitaceous taxa and evaluates their community assembly under environmental filtering by climate, host identity, plant developmental stage and management practices. The symbiotic relationship is maintained through layered mechanisms that balance host immune regulation, redox/ROS homeostasis, and hormone-mediated trade-offs between growth and defense alongside secondary metabolism (e.g., alkaloids), and microbiome restructuring process. We integrate pathogen and herbivore suppression with enhanced tolerance to individual abiotic stresses and critically evaluate the emerging evidence for combined drought-salinity and drought-heat conditions. Across individual and combined stress contexts, recurrent endophyte-associated responses include osmotic adjustment, antioxidant capacity and ion homeostasis. Panomics approaches integrating genomics, transcriptomics, metabolomics and comparative genomics information can identify biosynthetic gene clusters, secreted proteins, transporters and regulatory networks associated with stress adaptation and support the prioritization of candidate traits for functional validation. However, AI/ML-assisted trait prediction, gene-editing target prioritization, and field-ready breeding applications remain prospective and require rigorous functional and multi-environment validation. We conclude by highlighting the translational opportunities, while addressing limitations related to field consistency, livestock safety and ecological biosafety. Future priorities include panomics-guided field validation, synthetic biology, microbiome engineering and carefully validated predictive breeding strategies for resilient grassland systems under climate change.