Angiosperm Genome Duplications Coincided With Nine Prehistoric Environmental Upheavals

Genome duplication has occurred in many flowering plants, with extra copies of genetic instructions apparently helping them survive periods of extreme environmental stress. Researchers analysed the genomes of 470 angiosperm species to develop an evolutionary tree spanning roughly 150 million years of evolution. The team detected and dated 132 occasions when genomes duplicated long ago.

These 132 genome duplications clustered into nine prehistoric periods between 108 million and 14 million years ago. Almost all genome duplications coincided with major environmental or geological events such as climate change, changing oxygen levels or mass extinctions. One coinciding event was the asteroid impact at the end of the Cretaceous Period that killed off the non-avian dinosaurs.

A third of angiosperms today are polyploid, said Hengchi Chen at the University of Göttingen in Germany. But previous analyses suggested that old genome duplications are fairly rare. “Most polyploid organisms went extinct during long-term evolution,” said Chen.

Normally organisms that reproduce sexually have two copies of their chromosomes. Plants like potatoes and some wheat varieties have four copies of their chromosomes. Some plants might have eight copies of their chromosomes or more.

Polyploidy can stunt growth or make it difficult or impossible to successfully mate with non-polyploid relatives. In times of global chaos, however, polyploid plants appeared to flourish.

Chen and his colleagues wanted to understand why many genome duplications in angiosperms dwindled out millions of years ago while others persisted. The analysis showed that during periods of turmoil, factors such as extreme heat or cold may have increased the rate of polyploidy while extra genes conferred resilience to drought, salt exposure and rapid ecosystem change.

“The originally minor, polyploid individual that hides in the corner of the population somehow gets access to more resources, and it can also have this fitness advantage for the stress,” said Chen.

Angiosperms’ hyper-flexible, redundant genomes may be key to their success as a group, he added. Pamela Soltis at the Florida Museum of Natural History in Gainesville questioned how larger sampling might affect the results. “Despite the fact that this analysis is huge compared to previous work, 470 species is still only a very small fraction of angiosperm species,” said Soltis.

The total is close to 400,000, but new genomes are becoming available at “a very rapid pace,” she said. @NewScientist reported that the findings suggest angiosperms may have survived major environmental and ecological upheavals in Earth’s prehistory thanks to accidentally duplicated genomes. 008.