AMF-SporeChipprovides new insights into arbuscular mycorrhizal fungal pre-symbiotic hyphal growth dynamics at the cellular level

Abstract

SummaryArbuscular mycorrhizal fungi (AMF) form symbiotic associations with the majority of land plants and deliver a wide range of soil-based ecosystem services. Due to their conspicuous belowground lifestyle in a dark environment surrounded by soil particles, much is still to be learned about the influence of environmental (i.e., physical) cues on spore germination, hyphal morphogenesis and hyphopodium formation in AMF.To fill existing gaps in AMF knowledge, we developed a new microfluidic platform – termed theAMF-SporeChip– to immobiliseRhizophagusandGigasporaspores and confront pre-symbiotic hyphae with physical obstacles. In combination with timelapse microscopy, the fungi could be examined at the cellular level and in real-time.TheAMF-SporeChipallowed us to acquire movies with unprecedented visual clarity and therefore identify various exploration strategies of AMF pre-symbiotic hyphae. We witnessed anastomosis formation involving directed hyphal growth in a “stop-and-go” manner, yielding visual evidence of pre-anastomosis signalling and decision-making. Remarkably, we also revealed a so-far undescribed reversible cytoplasmic retraction as part of a highly dynamic space navigation.Our findings demonstrated how AMF employ an intricate mechanism of space searching, involving reversible cytoplasmic retraction, branching and directional changes. In turn, theAMF-SporeChipis expected to open many future frontiers for AMF research.