Flower power lies in genome downsizing
DNA dumping may be the answer to Charles Darwin’s “abominable mystery”.
Until about 140 million years ago, the world was dominated by conifers and ferns. Then flowering plants exploded onto the scene, conquering the planet with a speed that Charles Darwin, who liked his evolution slow, called “an abominable mystery”.
Botanists have long credited this success to the flowers’ ability to seduce different animal species into spreading their pollen.
A different and surprising explanation now comes from Kevin Simonin at San Francisco State University and Adam Roddy at Yale University. Success, they argue in the journal PLOS, resulted from genome downsizing.
Smaller genomes meant flowering plants could make smaller nuclei (which package up the genome inside the cell) and ultimately make more compact cells, says Simonin. More compact cells, “like smaller Lego blocks”, allowed them to pack their leaves more densely with structures like breathing pores (stomata) and densely branched veins.
That explains why flowering plants can photosynthesise at three times the rate of ferns and grow much faster.
“They couldn’t do that without the infrastructure,” says Tim Brodribb, at the University of Tasmania. “This is what allowed them to overrun the planet.”
In their study, “Genome downsizing, physiological novelty, and the global dominance of flowering plants”, Simonov and Roddy wondered if the size of plant genomes was linked to the size of cells.
To find out, they studied 400 species of ferns, gymnosperms (“naked seed” producers such as conifers) and flowering plants. The smaller the genome, they found, the tinier the cells and the greater the density of leaf stomata and veins.
The greatest variation was within flowering plants. A rare Japanese flower, Paris japonica, boasts the planet’s biggest genome at 150 billion base pairs of DNA. The smallest genome for a flowering plant is the carnivorous Genlisea aurea, with 63 million base pairs.
By shrinking their genome, flowering plants were able to shrink their cells and pack in more features.