"Plants, big or small, are the foundation of all life." This is David Attenborough's introduction to the famous documentary Green Planet.
Over the past 500 million years, plants have influenced every aspect of the planet. Today, they support all other life on Earth, providing the oxygen people need to breathe, the clean air they depend on, and cooling the planet.
But without water, plants cannot survive. Plants first appeared in aquatic environments, and it is estimated that about 500,000 species of land plants were produced by a single ancestor floating in the water.
In a paper published recently in The New Botanist, the team genetically studied how plants "learned" to use water during evolution. In the history of plant development, water as a key evolutionary driver has allowed key genes to "adopt" various strategies to evolve, so that the tiny bryophytes that first lived on land during the Cambrian period (about 500 million years ago) gradually evolved into the huge trees that form today's complex forest ecosystems.
How did plants evolve?
The relationship between plants and water has changed dramatically over the past 500 million years. Plants lived in freshwater and marine habitats before migrating to land. Spirogyra was one of the representative plants of the time, drifting with the flow and greedily absorbing the water around them. But the ancestors of these land plants had a very limited ability to regulate water on their own.
When plants first come to land to colonize, their first challenge is to find a new way to get nutrients and water without having to soak in water all the time. The next challenge they face is how to increase their size. Eventually, plants evolved to be able to survive even in very arid environments, such as deserts.
The evolution of these genes is critical to the survival of plants, but how do they help plants adapt first and thrive on land?
The research team analyzed and compared more than 500 genomes and found that different parts of plant anatomy that are involved in water transport, including pores (stomata), vascular tissue, and roots, are associated with different genetic evolution methods. This journey tells us how and why plants evolved at different points in their history.
Critical adaptations of life on land
Stomata are tiny pores on the surface of leaves and stems that absorb carbon dioxide when they are open and minimize water loss when closed.
New research has found that genes involved in stomatal development were present in the first land plants. This suggests that the first land plants already had genetic tools for building stomata, a key adaptation of terrestrial life.
Schematic diagram of the stomatal structure. | Image credit: Ali Zifan /Wikicommons
The speed of reaction of stomata opening and closing depends on the species. For example, the stomata of daisies close faster than those of ferns. Studies have shown that the stomata of the first land plants did close, but over time, this opening and closing ability accelerated as the species multiplied.
Gene duplication causes two copies of a gene to appear, which allows one to perform its original function while the other evolves a new function. With these new genes, the stomata of plants that grow from seeds can close and open more quickly, making them more adaptable to environmental conditions.
The new tricks of the old genes
Vascular tissue is a piping system for plants that helps transport water inside the plant and makes a breakthrough in size. If you've ever seen the rings of trees that were cut down, that's the remnants of vascular tissue growth.
Vascular beam microscopic photographs. | Image credit: Berkshire Community College Bioscience Image Library
The study found that vascular tissue evolved not through new genes, but through a process of genetic tinkering. That is, old genes are repurposed to gain new functions. This suggests that evolution doesn't always happen through new genes, but rather that old genes can learn new tricks.
Key new genes
In addition to stomata and vascular tissue, plants need to acquire a critical ability to truly "gain a foothold" on land. The evolution of roots allowed plants to obtain water from deep within the soil and provide anchoring.
The study found that some key new genes emerged in the ancestors of plants and seeds that lived on land, corresponding to the development of root hairs and roots. This demonstrates the importance of complex root systems that give ancient plants the ability to obtain precious water that was previously unavailable.
The relationship between plants and water evolves in a step-by-step manner. This diagram shows the evolutionary relationships of plants, and the black silhouette below illustrates the species of each taxon. Dotted lines pointing to different water regulation innovation points indicate their origins, and each color corresponds to an innovation point, indicating the genetic mechanisms associated with each innovation. The symbol description shows the number of new, duplicate, and augmented genes in the box. The main plant taxa are classified in color blocks at the bottom. As can be seen from the figure, the genes associated with stomatals, vascular tissue, and roots have evolved different "strategies." | Image credit: Bowles, A. et al. (2022)
Water, as an important factor in the evolution of plants, allowed these characteristics to evolve at every important step in plant history, culminating in the formation of the green planet we are today. This genetic analysis gives us a new understanding of the genetic basis and diversification process of plant evolution.
The plant world of the future
In addition to helping us understand the past, this research is equally important for the future.
By understanding how plants evolved, we can begin to understand some of the limiting factors of their growth process. For example, if researchers can determine the function of some key genes, they can begin to improve the ability of crop species to use water and resist drought. This is of particular importance for food security.
Plants may also help address some of the most pressing issues currently facing, such as reducing humanity's dependence on fertilizers while improving the sustainability of agriculture and reducing greenhouse gas emissions.
Nowadays, it is important to find ways to live in harmony on our green planet.
#创作团队:
Original author: Alexander Bowles (Postdoctoral Associate, University of Bristol)
Compile: Takeko
Typography: Wenwen
#参考来源:
https://theconversation.com/how-ancient-plants-learnt-to-use-water-when-they-moved-on-to-land-new-research-177009
https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.17981
http://www.bristol.ac.uk/news/2022/february/plants-evolved-to-colonise-land.html
#图片来源:
Cover image: pixabay
First image: pixabay