Availability of carbon and nitrogen in soil affects Metarhizium robertsii root colonization and transfer of insect-derived nitrogen

Phosphorus/nitrogen sensing and signaling in diverse root-fungus symbioses

Establishing mutualistic relationships between plants and fungi is crucial for overcoming nutrient deficiencies in plants. This review highlights the intricate nutrient sensing and uptake mechanisms used by plants in response to phosphate and nitrogen starvation, as well as their interactions with plant immunity. The coordination of transport systems in both host plants and fungal partners ensures efficient nutrient uptake and assimilation, contributing to the long-term maintenance of these mutualistic associations. It is also essential to understand the distinct responses of fungal partners to external nutrient levels and forms, as they significantly impact the outcomes of symbiotic interactions. Our review also highlights the importance of evolutionarily younger and newly discovered root-fungus associations, such as endophytic associations, which offer potential benefits for improving plant nutrition. Mechanistic insights into the complex dynamics of phosphorus and nitrogen sensing within diverse root-fungus associations can facilitate the identification of molecular targets for engineering symbiotic systems and developing plant phenotypes with enhanced nutrient use efficiency. Ultimately, this knowledge can inform tailored fertilizer management practices to optimize plant nutrition.

Exo- and endophytic fungi enable rapid transfer of nutrients from ant waste to orchid tissue

The epiphytic orchid Caularthron bilamellatum sacrifices its water storage tissue for nutrients from the waste of ants lodging inside its hollow pseudobulb. Here, we investigate whether fungi are involved in the rapid translocation of nutrients. Uptake was analysed with a 15 N labelling experiment, subsequent isotope ratio mass spectrometry (IRMS) and secondary ion mass spectrometry (ToF-SIMS and NanoSIMS). We encountered two hyphae types: a thick melanized type assigned to 'black fungi' (Chaetothyriales, Cladosporiales, and Mycosphaerellales) in ant waste, and a thin endophytic type belonging to Hypocreales. In few cell layers, both hyphae types co-occurred. 15 N accumulation in both hyphae types was conspicuous, while for translocation to the vessels only Hypocreales were involved. There is evidence that the occurrence of the two hyphae types results in a synergism in terms of nutrient uptake. Our study provides the first evidence that a pseudobulb (=stem)-born endophytic network of Hypocreales is involved in the rapid translocation of nitrogen from insect-derived waste to the vegetative and reproductive tissue of the host orchid. For C. bilamellatum that has no contact with the soil, ant waste in the hollow pseudobulbs serves as equivalent to soil in terms of nutrient sources.

Metarhizium: an opportunistic middleman for multitrophic lifestyles

Metarhizium spp. mediate multiple interactions that are usually positive with respect to their long-term plant environment, and negative with respect to short-lived hosts. In particular, their ability to kill a wide range of insects maximizes protection to the plants and provides a resource of nitrogen that the fungus trades with the plant for carbon. Here, we highlight emerging concepts underlying Metarhizium-plant-insect interactions. Experiments on model systems have provided detailed mechanistic knowledge of how these fungi interact with plants and insects, and a greater understanding of the evolutionary forces driving these interactions. However, further integration of studies at the ecological and mechanistic level is needed to evaluate the importance of Metarhizium's multitrophic interactions to the structuring of natural communities.

Different Cultivation Environments Affect the Yield, Bacterial Community and Metabolites of Cordyceps cicadae

Cordyceps cicadae is an entomogenous fungus with important uses in traditional Chinese medicine. However, its wild resources have not met consumers' demand due to excessive harvesting practices. Artificial cultivation is therefore an important alternative, but research on cultivating C. cicadae in natural habitats has not been reported. In this study, we aimed to explore the viability of cultivating C. cicadae in a natural habitat, in the soil of Pinus massoniana forest. We assessed and compared the yield, metabolite contents and bacterial community composition of C. cicadae grown in the Antheraea pernyi pupae at different growth stages, and under different cultivation conditions, in the soil of a natural habitat and in sterile glass bottles. Our results showed that cultivating C. cicadae in a natural habitat is feasible, with up to 95% of pupae producing C. cicadae fruiting bodies. The content of nitrogen compounds (amino acids) in C. cicadae cultivated in a natural habitat was significantly higher than in glass bottles, while the yield and carbon compound (mannitol and polysaccharide) and nucleoside (cordycepin and adenosine) contents were lower. Different bacterial genera were enriched in C. cicadae at different growth stages and cultivation environments, and these bacterial genera were closely related to metabolites contents during growth. This study demonstrated the viability of a novel cultivation method of C. cicadae, which could be used as an alternative to wild stocks of this fungus. These findings provided new insights into the growth mechanism of C. cicadae and its interaction with soil microorganisms.