Arbuscular mycorrhizal symbiosis (AMS) is a ubiquitous and ancient interaction between plant root systems and fungi of the Glomeromycotina subphylum. The resulting relationship is mutually beneficial and deeply intimate where the fungus intracellularly colonises root cortex cells to receive organic carbon and deliver minerals and water to the plant. Fungal colonisation of plant roots and cells is extremely dynamic and asynchronous across the root system. Symbiosis development must therefore result from spatio-temporally fine-tuned molecular control mechanisms of plant and fungus. Although the plant genetic program underpinning AMS has been extensively studied, little is known about its dynamic regulation across root cell layers and developmental stages of the association. Thus, many questions remain outstanding: how do different cell-types transcriptionally respond to AMS, how are distinct cell-type specific regulatory states coordinated, and what are the transcriptional activities in the fungus associated with discrete stages of root colonisation? The advent of single cell-based techniques now enables the high-resolution analysis to address these questions. In this review, we recapitulate the current knowledge on the spatio-temporal control of AMS, we evaluate the relevance of existing spatial datasets to AMS research and provide new perspectives for future study.

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