Influence of sugar metabolism on the dialogue between arbuscular mycorrhizal fungi and plants

Abstract Arbuscular mycorrhizal (AM) symbioses in plants are broadly significant because of their capacity to facilitate water and nutrient acquisition and thus, to promote vigorous growth and development among host plants. Many horticultural plants, especially citrus plants, are highly dependent on AM fungi. In return, AM fungi receive sugars and lipids from their host plants. The sugars (mainly sucrose) are transported from the aerial parts of host plants to the roots and thus, form a mycorrhizal carbon pool. In roots, sucrose is converted to hexoses, which are then taken up by AM fungal intraradical hyphae and converted to trehalose and glycogen for growth and storage in extraradical hyphae and potentially participate in the soil carbon cycle through as the glomalin-related soil proteins. Therefore, the root mycorrhizal carbon pool influences the sugar (mainly sucrose) metabolism of plants, providing a guarantee for mycorrhizal plants to maintain better plant growth, stress resistance, fruit quality, lateral root development, and soil carbon sequestration. Thus, sugar metabolism is a player in the dialog between AM fungi and plants. This review briefly summarizes the processes of sucrose synthesis, transport, and metabolism, and highlights the relationship between AM fungi and plant sugars with an emphasis on AM-carbon pools, osmotic adjustment, fruit quality, and sugar-associated gene expression. Future research prospects are discussed.