Role of mycelial networks of arbuscular mycorrhizal fungi in mobilizing symbiotic N-fixing bacteria

作者：Jiadong He · 发表于：Digital Access to Libraries · 年份：2025 · 研究领域：Mycorrhizal Fungi and Plant Interactions、Legume Nitrogen Fixing Symbiosis、Plant-Microbe Interactions and Immunity

Legumes rely on nitrogen (N)-fixing bacteria (rhizobia) and arbuscular mycorrhizal (AM) fungi to optimize nutrient acquisition, particularly in nutrient-poor soils. Rhizobia fix atmospheric N2 by forming root nodules, while AM fungi enhance nutrients uptake (e.g. P and N) and mediate soil microbe interactions. Although rhizobia recruitment is closely linked to the production of flavonoids by plants, this is limited to a few millimeters from the roots. The mechanisms enabling long-distance rhizobial migration and ensuring host-specific recruitment remain poorly understood. Here, we investigated the role of AM fungal extraradical mycelium (ERM) and common mycorrhizal networks (CMNs) in facilitating rhizobial migration and host specific recruitment by legumes. Using Medicago truncatula and Sinorhizobium meliloti, we demonstrated that the ERM of Rhizophagus irregularis provides a physical pathway for long-distance rhizobial migration. Time-lapse microscopy revealed that the bacterium moved along the surface of the fungal hyphae supported by cytoplasmic flow within the fungal network that can improve the supply of nutrients to the bacterium and signal the presence of a suitable host. Metabolomic analyses identified eight flavonoids unique to ERM connected to M. truncatula, which enhanced rhizobial growth and expression of genes involved in nodulation. These findings demonstrate that AM fungal ERM extends rhizobial recruitment beyond the rhizosphere, allowing legumes to attract the...