Could ergothioneine serve as an indicator of functional plant-AMF interactions in crop plants?

Improving the functional benefits of arbuscular mycorrhizal fungi (AMF) is considered an important part of developing more sustainable and resilient crop production systems. However, the outcomes of AMF symbioses vary substantially depending on environmental conditions, soil fertility, fungal community composition, and host genotype. Even among varieties of the same crop species, responses to AMF colonization can differ considerably, yet methods for quantifying functional plant-AMF interactions remain labour-intensive and often fail to capture symbiotic efficiency directly. Here, we propose that ergothioneine (EGT), a sulfur-containing antioxidant amino acid whose accumulation in plants appears to be strongly influenced by AMF-associated pathways, may serve as an integrated biochemical indicator of functional AMF-mediated nutrient exchange. We hypothesize that variation in plant EGT accumulation between crop varieties reflects differences in the regulation and functional performance of plant-AMF interactions, possibly including symbiotic signalling, carbon allocation, nutrient exchange efficiency, and/or rhizosphere microbial dynamics. We present new results showing differences in grain EGT concentration among five spring wheat varieties, supporting the possibility that host genotype influences AMF-associated EGT accumulation. We discuss potential mechanisms underlying these differences, evaluate alternative explanations, and outline experimental approaches for testing the relationship between EGT accumulation and functional plant-AMF interactions. If validated, EGT quantification could provide a scalable and straightforward approach for identifying crop genotypes with enhanced responsiveness to AMF-mediated nutrient acquisition, with potential applications in breeding and management strategies for low-input and ecologically sustainable agriculture.