Grapevines look fairly placid, but new research has shown that one of our more popular varieties—Pinot Noir—has been aggressively fighting off viral attacks for centuries. And according to a team at Australia's University of Queensland, the variety's success may be due to its ability to assimilate vanquished viruses' DNA into its own genes, evolving in the process.
According to the study, written by Dr. Andrew Geering, a plant pathologist at the university, and published in Nature Communications, he and his team found that Pinot Noir contains the genetic material of viruses believed to be in excess of 30 million years old.
With this discovery comes evidence that plants have been genetically modifying themselves long before modern scientists ever tried to mess with their genetic code. “Normally, individuals acquire new DNA via sexual reproduction," Geering told Wine Spectator. "What we have observed is horizontal gene transfer, where the plant has acquired DNA from a very distantly related organism, similar to what we see in genetic engineering.”
Viruses are microbes that replicate themselves using living cells in other organisms. When a virus attacks a plant, the stakes can be life or death. When the plant manages to recover, it typically doesn’t emerge from the battle unscathed. But the plant can co-opt some of the vanquished virus’ DNA to repair damage done from the attack, altering itself in the process.
Geering likens it to applying putty to a crack in the wall, albeit on a microscopic level. “The plant has been able to rid itself of the viral infection, but fragments of viral DNA have been captured in the plant’s genome," he said. "In response, the plant uses it to fill the breaks, the genetic cracks left over from the attack.”
This behavior supports Geering’s hypothesis that these viral insertions may be contributing in a positive way to the success of the plant itself. Vintners have been selecting and grafting vines for centuries to keep preferred qualities. But vines do evolve and change. “When a farmer propagates a vine by cutting or grafting, the progeny are identical to the parent. This raises the question of how genetic variation could be generated," Geering said.
He cites previous research that found differences between Pinot Noir vines in the patterns of insertion of viral DNA. "While currently there is no direct proof that insertion of the viral DNA has improved wine quality, it does indicate that the capture of viral sequences is an important process in producing genetic variation,” he said.
A strong reason to conclude that this extraneous DNA material helps the plant is the simple fact that it is kept in the first place. “We presume that the captured viral DNA aids the plant, as otherwise it would be genetic baggage and quickly eliminated,” added Geering. “We hypothesize that there has been some selective advantage conferred to the plant by incorporation of the viral DNA: this selective advantage might be a natural one such as disease resistance or it might be a human-imposed selection pressure like the selective propagation of desirable clones.”
In the future, researchers hope to isolate and identify the genetic basis of the traits that make Pinot Noir so distinctive. Molecular techniques could then be developed to assist with plant breeding. “Our study is only one part of a giant puzzle, but integrated viruses are obviously a significant part of the grape’s genetic make-up,” said Geering.