Study finds ancient algae knew how to survive on land before leaving water

Ancient algae were already genetically pre-adapted to inhabit land, before it left water, went on to evolve into the world's first plant and colonize the earth, a study said Monday.

The study, conducted by a team of scientists from the University of Wisconsin, Madison, and other international collaborators and published in the U.S. journal Proceedings of the National Academy of Sciences, solved a long-running mystery about the first stages of plant life on earth.

"Without the development of this pre-adapted capability in alga, the earth could be a very different place today," said lead author Pierre-Marc Delaux of the University of Wisconsin, Madison.

Up until now it had been assumed that the algae evolved the capability to source essential nutrients for its survival after it arrived on land, by forming a close association with a beneficial fungi called arbuscular mycorrhiza (AM), which still exists today and which helps plant roots obtain nutrients and water from soil in exchange for carbon.

The previous discovery of 450 million year old fossilized spores similar to the spores of the AM fungi suggested this fungi would have been present in the environment encountered by the first land plants.

Remnants of prehistoric fungi have also been found inside the cells of the oldest plant macro-fossils, reinforcing this idea.

However, scientists were not clear how the algal ancestor of land plants could have survived long enough to mediate a quid pro quo arrangement with a fungi.

In the new study, Delaux and colleagues analyzed DNA and RNA of some of the earliest known land plants and green algae and found evidence that their shared algal ancestor living in the Earth's waters already possessed the set of genes it needed to detect and interact with the beneficial AM fungi.

The team believed this capability was pivotal in enabling the algae to survive out of the water and to colonize the earth.

By working with the fungi to find sustenance, the algae were able to buy time to adapt and evolve in a very different and seemingly infertile environment, it said.

"At some point 450 million years ago, alga from the earth's waters splashed up on to barren land. Somehow it survived and took root, a watershed moment that kick-started the evolution of life on earth," Delaux said. "Our discovery shows for the first time that the alga already knew how to survive on land while it was still in the water. This finding has filled a gap in our collective knowledge about the origins of life on earth." Endit