Summary Orchids are highly dependent on their mycorrhizal fungal partners for nutrient supply, especially during early developmental stages. In addition to organic carbon, nitrogen (N) is probably a major nutrient transferred to the plant because orchid tissues are highly N‐enriched. We know almost nothing about the N form preferentially transferred to the plant or about the key molecular determinants required for N uptake and transfer. We identified, in the genome of the orchid mycorrhizal fungus Tulasnella calospora, two functional ammonium transporters and several amino acid transporters but found no evidence of a nitrate assimilation system, in agreement with the N preference of the free‐living mycelium grown on different N sources. Differential expression in symbiosis of a repertoire of fungal and plant genes involved in the transport and metabolism of N compounds suggested that organic N may be the main form transferred to the orchid host and that ammonium is taken up by the intracellular fungus from the apoplatic symbiotic interface. This is the first study addressing the genetic determinants of N uptake and transport in orchid mycorrhizas, and provides a model for nutrient exchanges at the symbiotic interface, which may guide future experiments.

No abstract

 All orchids rely on mycorrhizal fungi for organic carbon, at least during early development. Orchid seed germination leads in fact to the formation of a protocorm, a heterotrophic postembryonic structure colonized by intracellular fungal coils, thought to be the site for nutrients transfer. The molecular mechanisms underlying mycorrhizal interactions and metabolic changes induced by this peculiar symbiosis in both partners remain mostly unknown.  We studied plant-fungus interactions in the mycorrhizal association between the Mediterranean orchid Serapias vomeracea and the basidiomycete Tulasnella calospora using non-targeted metabolomics. Plant and fungal metabolomes obtained from symbiotic structures were compared with those obtained under asymbiotic conditions.  Symbiosis induced profound metabolomic alterations in both partners. In particular, structural and signaling lipid compounds sharply increased in the external fungal mycelium growing near the symbiotic protocorms, whereas chito-oligosaccharides were identified uniquely in symbiotic protocorms.  This work represents the first description of metabolic changes occurring in orchid mycorrhiza. These results-supported by transcriptomic data-provide novel insights on the mechanisms underlying the orchid mycorrhizal association and open intriguing questions on the role of fungal lipids in this symbiosis.

No abstract

SUMMARYOrchid mycorrhiza (OM) represents an unusual symbiosis between plants and fungi because in all orchid species carbon is provided to the host plant by the mycorrhizal fungus at least during the early stages of orchid development, named a protocorm. In addition to carbon, orchid mycorrhizal fungi provide the host plant with essential nutrients such as phosphorus and nitrogen. In mycorrhizal protocorms, nutrients transfer occurs in plant cells colonized by the intracellular fungal coils, or pelotons. Whereas the transfer of these vital nutrients to the orchid protocorm in the OM symbiosis has been already investigated, there is currently no information on the transfer of sulfur (S). Here, we used ultra‐high spatial resolution secondary ion mass spectrometry (SIMS) as well as targeted gene expression studies and laser microdissection to decipher S metabolism and transfer in the model system formed by the Mediterranean orchid Serapias vomeracea and the mycorrhizal fungus Tulasnella calospora. We revealed that the fungal partner is actively involved in S supply to the host plant, and expression of plant and fungal genes involved in S uptake and metabolism, both in the symbiotic and asymbiotic partners, suggest that S transfer most likely occurs as reduced organic forms. Thus, this study provides original information about the regulation of S metabolism in OM protocorms, adding a piece of the puzzle on the nutritional framework in OM symbiosis.

Grifola frondosa (“Maitake”) is an edible fungus with several nutraceutical properties, largely used in traditional medicine. The increased use of Maitake as a food supplements ingredient raised the need of accurate authentication methods since the morphological identification of G. frondosa is not feasible in formulated food supplements. We developed a diagnostic tool based on loop-mediated isothermal AMPlification (LAMP) for the detection of G. frondosa in food supplements. First, a modified CTAB protocol for DNA extraction from food supplements has been set up and it has been shown to be able to isolate amplifiable total genomic material from different types of commercial products. Subsequently, the LAMP assay confirmed high specificity and good analytical sensitivity, allowing to detect up to 0.62 pg of genomic DNA in less than 20 min. Ten related fungal species resulted negative, confirming the specificity of the assay. The presence of Maitake in commercial food supplements was confirmed, except for one, revealing a mislabeling (or a food fraud). This assay proved to be a rapid powerful tool for food authentication purposes and routine inspections at any level of the supply chain of Maitake-based products and it can be used as a model for other quality control assays of fungal food products. Supplementary Information The online version contains supplementary material available at 10.1007/s12161-022-02235-0.