Arbuscular mycorrhizal fungi as master engineers of plant ion homeostasis under salt stress: a review

Abstract

Soil salinity disrupts the balance of plant ions by promoting the accumulation of both Na + and Cl − while simultaneously impairing the acquisition of K + , Ca 2+ , and Mg 2+ , thereby compromising cellular function and reducing crop productivity. Arbuscular mycorrhizal fungi (AMF) form symbiotic associations with most land plants and have evolved sophisticated strategies to counteract these effects. This review extends traditional descriptions of AMF-enhanced nutrient uptake by presenting a “multi-barrier” model of ion homeostasis that integrates fungal structural sequestration with plant molecular regulation. Within this framework, AMF function conceptually as an ionic fortress: extraradical hyphae selectively filter soil ions, intraradical vesicles sequester Na + and Cl − crystals, arbuscules serve as regulated exchange interfaces, and fungal ENA ATPases likely contribute to Na + extrusion. Concurrently, AMF modulate host plant transcriptomes, upregulating key transporters including SOS1 (plasma membrane Na + /H + antiporter), NHX (vacuolar Na + /H + exchanger), HKT (xylem Na + unloading), AKT/SKOR (K + channels), and CLC (Cl − channels). This dual fungal-plant system consistently reduces shoot Na + accumulation, elevates K + /Na + ratios, and improves the salt tolerance across diverse species. We further synthesize species-specific responses, synergies with plant growth-promoting bacteria, and knowledge gaps. By synthesizing evidence for AMF as active participants in ion homeostasis rather than passive helpers, this review provides a conceptual framework for developing mycorrhiza-based solutions for saline agriculture.