Epigenetic regulation of mycorrhizal symbioses: from plastic responses to transgenerational legacies.

Mycorrhizal symbioses represent one of the most widespread and ecologically significant plant-microbe interactions, shaping plant nutrition, stress resilience, and ecosystem functioning. Beyond their role in nutrient exchange and systemic defense, growing evidence suggests that these symbioses also influence plant plasticity within and across generations through epigenetic regulation. These mechanisms operate throughout the mutualistic interaction, from fungal recognition and root colonization to symbiosis functioning, by regulating gene networks that control signaling, defense suppression, and nutrient exchange. By integrating environmental cues into potentially heritable gene regulatory states, epigenetic regulation fine-tunes within-generation responses and may also contribute to effects across generations, thereby influencing adaptation and resilience. The extent of mycorrhiza-induced epigenetic inheritance likely depends on the host's reproductive strategy and lifespan. Clonal propagation and shorter-lived hosts tend to preserve epigenetic marks, whereas sexual reproduction and longer-lived species show partial resetting. This contrast shapes offspring performance, ecological interactions, and evolutionary trajectories. Here, we synthesize current knowledge on the epigenetic regulation of mycorrhizal symbioses, draw parallels with other plant-microorganism interactions (including plant-pathogens and plant-endophytes), highlight its role in within-generation plasticity and propose a potential role across generations. We outline future research directions to disentangle the stability, ecological relevance, and evolutionary significance of mycorrhiza-mediated epigenetic inheritance.