Multilevel analysis between Physcomitrium patens and Mortierella explores potential long-standing interaction among land plants and fungi

The model moss species Physcomitrium patens has long been used for studying divergence and evolution of land plants spanning from bryophytes to angiosperms. In addition to its phylogenetic relationships, the limited number of differential tissues, and comparable morphology to the earliest embryophytes make it an ideal candidate for modeling plant terrestrialization 500 million years ago. Based on how plants and fungi interact today, it is predicted that early interactions may have aided in overcoming the barriers present for initial plant colonization on land. This may have manifested similar to present day, where fungi enabled easier uptake of nitrogen, phosphorous, micronutrients, and water retention in exchange for a reliable carbon source. However, identifiable fungal symbionts in P. patens, despite mutualistic interaction widespread among all present day embryophyte families, have remained elusive. To test modern representatives of early land fungal lineages, two Mortierella species (Linnemannia elongata and Benniella eriona), with strains lacking and containing endobacterial symbionts, were grown in coculture with P. patens. We illustrate the interaction between P. patens and Mortierella through high-throughput phenomics, microscopy, RNA-sequencing, differential expression profiling, gene ontology enrichment, and comparisons among 99 other P. patens transcriptomic studies. Our study provides insights into the earliest plant-fungal interactions may have looked like and ways P. patens and Mortierella communicate today.