Small Genomes Helped Flowering Plants Expand Across Earth

Researchers from San Francisco State University and Yale University may have finally discovered how flowering plants were able to quickly dominate ecosystems across the world, a new study in PLOS Biology reports.

The rapid spread of flowering plants across the world is something Charles Darwin — who referred to it as an “abominable mystery” — struggled to understand during his lifetime. While such species are the most populous on Earth, nobody has been able to figure out how they moved as quickly as they did.

In the new research, the team discovered that the plants have small cells relative to other major plant groups, a key difference that was made possible by a greatly reduced genome size.

Though researchers have not been able to figure out why flowering plants have had so much success, studies from the past 30 years show that they have unparalleled rates of photosynthesis compared to other flora. That increased level of production allowed them to grow quickly and outcompete the ferns and conifers that dominated ecosystems for hundreds of millions of years.

However, though scientists have known about the increased rates, they could not figure out how the plants managed to evolve leave capable of such high production. 

To shed light on that process, the scientists in the recent study looked over past studies and found that many authors believe the efficient leaves are directly linked to the flowering plants’ genome size. As each cells has one copy of the plant’s genome, smaller genomes lead to smaller cells. Then, smaller cells — including ones specialized for nutrient transport — can be packed into a tighter amount of space. Shrinking the cell sizes makes water and nutrient delivery much more efficient as well.

After looking at hundreds of different species, the team found that genome downsizing began about 140 million years ago and coincided with the spread of the earliest flowering plants around the world.

This research answers a large question, but it also creates many more. Now that scientists have insight into flowering plants, they next want to see why the species were able to shrink their genomes more than other plant groups and what specific innovations in genome structure the plants exploited.