Microalgae proves to possibly be the oldest organism exploited by the Biotech industry. Now a mass research collaboration from Wisconsin (US), Cologne (Germany), Toulouse (France) and Norwich (UK) amongst others have published in PNAS that the microalgal genes needed for bacterial and fungal symbiosis were originally present before the transition of ancient plants to land.
The transition of plants to land from the ocean has been shown to have occurred in the early Devonian period around 450 millions years ago, paving a way for Metazoans (animals) to also colonize the barren landmasses. Green algae (Charophyta and Chlorophyta) can exist freely in water-masses, whereas land plants (Embryophyta) require adaptations for vascularisation and root support in order to thrive. For a much more in depth understanding of the current phylogenetic relationships in plant evolution check out this review by Leliaert et al. (here).
Fossil records have since revealed that extinct species of arbuscular mycorrhizal (AM) spores were present around the same time.