Nutrient exchange in the symbiosis
The whole complexity of the symbiotic interaction allows to maintain a balanced nutrient exchange between the plant and the AM fungus and avoid a parasitic situation. We would like to know which nutrients and at which interfaces are exchanged in this symbiosis. Currently, is accepted that AM fungi receive carbohydrates and lipids from their host plants, and deliver, in exchange, a series of mineral nutrients, most prominently phosphate. We identified a characterized the first bonafide AM fungal monosaccharide transporter that takes up sugars from the root (see Helber et al., 2011). In that paper, we were also able to establish HIGS (host induce gene silencing) to inactivate fungal genes, as AM fungi are recalcitrant to gene manipulation (Helber et al., 2008). We have also shown that AM fungal colonization significantly alters the root expression and localization of the novel sugar exporters/importers SWEETs, suggesting that they might be partly responsible for the carbohydrate supply to AM fungi (Manck-Götzenberger and Requena, 2016; Tamayo et al., 2022).