Trends in Ecology & Evolution
The land flora: a phototroph-fungus partnership?
Section snippets
Terrestrial algae repeatedly interacted with fungi
Terrestrial microscopic phototrophs, unicellular or filamentous, belong to cyanobacteria and green algae (e.g. Trentepohlia, Pleurococcus) and are either free-living or more frequently associated with mutualistic fungi, to form lichens[6]. As shown by molecular approaches[7], lichen-forming fungi arose many times during the evolution of both Ascomycotina and Basidiomycotina. Lichens, in which the alga is protected by the fungal stroma, tolerate a wide range of conditions[8]under which neither
Plants are ancestrally mutualistic with glomales
Land colonization by multicellular phototrophs involved the radiation of the `Plantae' (a particular subgroup of green algae phylogenetically independent of terrestrial green microalgae) during the Silurian, with possible precursors during the Ordovician[2](Appendix B). These phototrophs, probably derived from Charophyta, share an egg-protecting archegonium and are divided into two main lineages: Atrachaetae (mosses, hepatics and hornworts) and Tracheophytae (vascular plants). Vascular plants,
Plants repeatedly interacted with septate fungi
Although the majority of advanced groups, such as grasses, retained the primitive VA mycorrhiza, other plants associated with septate fungi. Numerous trees and some shrubs (Gymnosperms, Gnetales and Angiosperms) form the so-called ectomycorrhizae (EcM) with septate fungi, Ascomycotina or Basidiomycotina, that grow intercellularly in the roots (Appendix A)[20]. The oldest known fossil EcM were found on Pinus roots from the Eocene[32], demonstrating that EcM were already established at least 50
Why 1+1>2 in terrestrialization
Adaptation to terrestrial life has often arisen through symbiosis, which brought together genetic material having different and complementary characteristics. The two partners are partly `preadapted' to live on land. The mycelial habit is well adapted to three-dimensional exploration of the substrate. Some mycobionts have a huge weathering potential, that allows access to non-soluble mineral elements44a, 44b, or even saprotrophic ability, that compensates for the low availability of mineral
Acknowledgements
We thank D.G. Garbary, M. Kluge, J. Kohlmeyer and T.N. Taylor for helpful discussion, and the authors who provided illustrations. We are grateful to K.A. Pirozynski for critically reading the manuscript. M-A. Selosse is on leave from Ecole Nationale du Génie Rural, des Eaux et des Forêts.
References (51)
Fungal associations in the terrestrial palaeoecosystem
Trends Ecol. Evol.
(1990)- et al.
Multi-functionality and biodiversity in arbuscular mycorrhizas
Trends Ecol. Evol.
(1995) - et al.
The origin of land plants: a matter of mycotrophism
BioSystems
(1975) - et al.
Phylogenetic origins of the asexual mycorrhizal symbiont Cenococcum geophilum Fr. and other mycorrhizal fungi among ascomycetes
Mol. Phyl. Evol.
(1996) - et al.
Life on land in the Precambrian
Science
(1994) - Taylor, T.N. and Taylor, E.L. (1993) The Biology and Evolution of Fossil Plants, Prentice...
- et al.
The distribution of arbuscular mycorrhizas in the British flora
New Phytol.
(1993) - et al.
Dating the radiations of the true fungi
Can. J. Bot.
(1993) - Ahmadjian, V. (1993) The Lichen Symbiosis,...
Multiple origins of lichen symbioses in fungi suggested by SSU rDNA phylogeny
Science
(1995)