Unraveling the network

Abstract

The arbuscular mycorrhhiza (AM) symbiosis involves an intricate network of signaling and biochemical pathways designed to ensure that a beneficial relationship is established between the plant and fungal partners as a result of a mutual nutrient exchange. Emerging data has been recently published to explain why the relationship is not always fair, as observed in prevalent parasitic AM relationships in which the plant host receives no phosphorus (P) in exchange for carbon (C) delivered to the fungus. The theory behind this unorthodox view of the AM relationship, together with the description of other recent developments in nutrient mobilization as well as in key aspects of the bi-directional signaling that culminates in the symbiotic association, is the subject of this review.

The effects of plant type, AMF inoculation and water regime on rhizosphere microbial communities

“…Although nutrient limitation might be a possible explanation because fungal hyphae have large N requirements (Hodge & Fitter, 2010), the concentration of NO 3 − and P in inoculated soils remained high, suggesting that C-limitation was a more likely explanation. The establishment of the symbiotic relation between AM fungus and plant requires an expenditure of C from the plant (Délano-Frier & Tejeda-Sartorius, 2008), potentially limiting C availability to microbes in the rhizosphere.…”

Rhizoglomus intraradices Improves Plant Growth, Root Morphology and Phytohormone Balance of Robinia pseudoacacia in Arsenic-Contaminated Soils

“…Under the HM stress condition, AMF also regulate the balance of the phytohormones by intervening in the communication of signals during the process of AMF-plant symbiotic association (Smith and Read, 2008;Li et al, 2018). Phytohormones, as a kind of endogenous plant signal, are the most sensitive responders in these processes, and they stimulate plants to show appropriate responses to adapting to HM stress (Ludwig-Müller, 2000;Délano-Frier and Tejeda-sartorius, 2008). Therefore, AMF contribute to building a productive, healthy, and sustainable ecosystem, with vegetation recovery in HM-contaminated areas.…”

AM-Induced Alteration in the Expression of Genes, Encoding Phosphorus Transporters and Enzymes of Carbohydrate Metabolism in Medicago lupulina

“…symbiotic system) was determined not only in arbuscules but also in the intercellular hyphae, which indicated that both structures appear to be important for sugar unloading [44]. The mycelium of the AM fungi probably receives carbohydrates from the apoplast of the root cortex [5] as glucose [46], and less as sucrose [2]. The exact location and mechanism of carbon transfer from host plants to AM fungi is not yet fully discovered, but it is the focus of recent studies of plant-microbial symbiotic interactions [17,18,[27][28][29]33].…”

“…Plant carbohydrate metabolism was shown to change significantly during AM formation. The host plant transfers up to 30% of assimilates towards the AM fungus [2,25]. Besides carbohydrates, it donates other metabolites, such as fatty acids, known to be used as a source of organic carbon directed in the synthesis of fungal lipids [26].…”

“…In AM symbiosis, the host plant supplies AM fungus with photosynthates in the form of hexose [2] and, to a lesser extent, sucrose [2][3][4]. The plant, in turn, receives water and a number of macro-and microelements, especially phosphorus [5].…”