Format: ORAL

Silvia Pressel1, Katie Field2, Martin Bidartondo3, Roberto Ligrone4 Jeffrey Duckett1

1 Natural History Museum, London, UK; 2 School of Biosciences, University of Sheffield, Sheffield, UK; 3 Department of Life Sciences, Imperial College London, UK; 4 Università degli Studi della Campania, Caserta, Italy.

Light microscope studies, many dating back to the nineteenth century, showed the ubiquitous presence of fungi in many liverworts and hornworts. Their identity and function were unknown. Transmission electron microscopy revealed the endophytes as belonging to a range of major fungal groups; Ascomycota in the rhizoids of Cephaloziaceae, Cephaloziellaceae, Lepidoziaceae, Schistochilaceae and Mylia anomala where the fungus induces rhizoid swelling and branching, Basidiomycota in the stems of Scapaniaceae and in the thalli of Aneuraceae, and Mucoromycota (Glomeromycotina and Mucoromycotina) in the Haplomitriopsida, hornworts and many simple and complex thalloid liverworts. The demonstration of healthy fungi in healthy host cells and specialised interfaces comparable to those of mycorrhizal associations in vascular plants, were strongly indicative of symbiotic relationships.  Sequencing enabled more precise identification of the fungi. The rhizoid ascomycete is Rhizoscyphus ericae, with the exception of Meliniomyces in Mylia anomala, the same fungi as in ericaceous hair roots. The basidiomycete genus Serendipita is found in leafy liverwort families but a later fungal lineage, Tulasnella, is the endophyte in the Aneuraceae.  Underlying their unusual cytology, also found in some Devonian fossils, the endophytes in the Haplomitriopsida are exclusively members of the subphylum Mucoromycotina whereas hornworts, simple and complex thalloids contain a mixture of Glomeromycotina and Mucoromycotina. From the first establishment of symbiosis, in the Haplomitriopsida, at the foot of the land plant tree, liverwort evolution has witnessed several gains and losses of fungi. Microcosm experiments combined with anatomical analyses are now demonstrating major differences in nutrient exchanges between Mucoromycotina and Glomeromycotina fungi and in their response to elevated carbon dioxide levels on a par with those at the dawn of plant terrestrialisation.  Ultrastructural observations of living hyphae in close proximity to Nostoc colonies suggest potential plant-fungus-cyanobacterium synergistic interactions in hornworts.