Adaptations of endophyte-infected cool-season grasses to environmental stresses: Mechanisms of drought and mineral stress tolerance
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Coolseason grasses infected with Neotyphodium spp. endophytes have an extraordinary impact on the ecology and economy of pasture and turf. A range of adaptations of endophyteinfected grasses to biotic and abiotic stresses has been identified but mechanisms of these adaptations are not clearly understood. In this review, we present recent research progress on endophyterelated mechanisms affecting abiotic (drought, mineral) and selected aspects of biotic stress tolerance in coolseason grasses. Endophytes induce mechanisms of drought avoidance (morphological adaptations), drought tolerance (physiological and biochemical adaptations), and drought recovery in infected grasses. Mineral nutrition (nitrogen, phosphorus, calcium) affects production of ergot alkaloids, thus understanding mechanisms involved in mineral economy of endophyteinfected grasses will help in developing management practices to reduce forage toxicity to livestock. Previous research resolved the role of endophyte in nitrogen (N) economy of tall fescue. We identified two endophyterelated mechanisms in tall fescue operating in response to phosphorus (P) deficiency. The mechanisms are altered root morphology (reduced root diameters and longer root hairs) and chemical modification of the rhizosphere resulting from exudation of phenoliclike compounds. These mechanisms were shown to benefit endophyteinfected plants grown under P deficiency. We also report a mechanism of aluminum (Al) sequestration on root surfaces in endophyteinfected tall fescue, which appears to be related to exudation of phenoliclike compounds with Alchelating activity. Understanding mechanisms of abiotic stress tolerance in endophyteinfected grasses is essential for continued improvement and persistence of grasses for a range of applications, e.g., forage for semiarid areas or cover plants for soil renovation.
