How Ancient Plants Began using Water when they Moved on to Land

By Alexander Bowles

"Plants, whether they are enormous, or microscopic, are the basis of all life including ourselves." This was David Attenborough's introduction to The Green Planet, the latest BBC natural history series.

Over the last 500 million years, plants have become interwoven into every aspect of our lives. Plants support all other life on Earth today. They provide the oxygen people breathe, as well as cleaning the air and cooling the Earth's temperature. But without water, plants would not survive. Originally found in aquatic environments, there are estimated to be around 500,000 land plant species that emerged from a single ancestor that floated through the water.

In our recent paper, published in New Phytologist, we investigate, at the genetic level, how plants have learnt to use and manipulate water—from the first tiny moss-like plants to live on land in the Cambrian period (around 500 million years ago) through to the giant trees forming complex forest ecosystems of today.

How plants evolved

By comparing more than 500 genomes (an organism's DNA), our results show that different parts of plant anatomies involved in the transport of water—pores (stomata), vascular tissue, roots—were linked to different methods of gene evolution. This is important because it tells us how and why plants have evolved at distinct moments in their history.

Plants' relationship with water has changed dramatically over the last 500 million years. Ancestors of land plants had a very limited ability to regulate water but descendants of land plants have adapted to live in drier environments. When plants first colonized land, they needed a new way to access nutrients and water without being immersed in it. The next challenge was to increase in size and stature. Eventually, plants evolved to live in arid environments such as deserts. The evolution of these genes was crucial for enabling plants to survive, but how did they help plants first adapt and then thrive on land?