Approximately 86 million years ago, after a mistake in cell division, the entire Welwitschia genome doubled during a time of increased aridity and prolonged drought in the region — and possibly the formation of the Namib Desert itself, said Tao Wan, a botanist at the Fairy Lake Botanical Garden in Shenzhen, China, and lead author of the study. He said that “extreme stress” is often associated with such genome duplication events.
Dr. Leitch, a co-author of the study, added that duplicated genes are also released from their original functions, potentially taking on new ones.
However, having more genetic material comes with a cost, Dr. Wan said. “The most basic activity for life is DNA replication, so if you have a big genome, it is really energy consuming to maintain life,” especially in such a harsh environment.
To make matters worse, a large amount of Welwitschia’s genome is “junk” self-replicating DNA sequences called retrotransposons. “Now that junk needs to be replicated, repaired,” Dr. Leitch said.
The researchers detected a “burst” of retrotransposons activity one to two million years ago, most likely because of increased temperature stress. But to counteract this, the Welwitschia genome underwent widespread epigenetic changes that silenced these junk DNA, through a process called DNA methylation.
This process, along with other selective forces, drastically pared down the size and energetic maintenance cost of Welwitschia’s duplicated library of DNA, Dr. Wan said, giving it “a very efficient, low-cost genome.”
The study also found that Welwitschia had other genetic tweaks hidden up its leaves.
The average plant leaf grows from the plant’s apexes, or the tippy-tops of its stem and branches. But Welwitschia’s original growing tip dies, and leaves instead pour out of a vulnerable area of the plant’s anatomy called the basal meristem, which supplies fresh cells to the growing plant, Dr. Wan said. A large number of copies or increased activity of some genes involved with efficient metabolism, cell growth and stress resilience in this area may help it continue to grow under extreme environmental stress. In a warming world, the genetic lessons Welwitschia has to offer may help humans breed hardier, less thirsty crops.