Strawberries are a prized delicacy with their large red berries and sweet flavor that make them an appetizing jam, a stand-alone afternoon snack, or a topping for almost any dessert. But strawberries are more than just a delicious treat. Hidden beneath the surface of its bright red fruit is a unique branch of the evolutionary tree. Strawberry’s genetic idiosyncrasies are ripe for scientists to study and gain fundamental insights into how organisms can evolve new, complex and versatile functions.
The first peculiarity of the strawberry genome is what scientists call polyploidy, meaning there are multiple sets of chromosomes within the cell. Humans are diploid. So you have two sets of chromosomes. Every individual gets one set from the father’s sperm donor and one set from the mother’s egg donor. Strawberries, on the other hand, are octaploid and have eight sets of chromosomes. seriously.
The second peculiarity is hybridization. Different species mate with each other to produce offspring that contain the genomes of both species. (In most organisms, mating or breeding results in a mashup of the genome, and not all are transplanted.)
In 2019, my colleagues and I published the first high-quality strawberry genome, revealing that the octoploid genome arose through a stepwise process. At some point over a million years ago, two ancient diploid species interbred to produce an extinct plant species with four sets of chromosomes. That seed hybridized with his third diploid seed to produce six sets of chromosomes, and he then hybridized with his fourth diploid seed to produce eight sets of chromosomes. bottom. This ancient wild octoploid then spread throughout the Western Hemisphere and split into his two species, which were collected by European settlers in the 18th century. These plants underwent a final crossbreeding event in continental Europe about 300 years ago to create the strawberries you know and love in your grocery store or garden.
What this means is that strawberries have on average eight copies of every gene, and every cell has genetic diversity equivalent to four different species. It is the driving force, and having multiple copies of a gene allows one copy to perform an essential function, while additional copies are free to participate in new activities and functions. Two of his recent studies illustrate this benefit. First, a study led by researchers at the University of Pittsburgh found that ploidy in strawberry species not only improved survival and reproduction in favorable environments, but also made them more resistant to stress in unfavorable environments. I found As the researchers noted, their findings fit the hypothesis that polyploidy can make plants both “jacks-of-all-trades” and “some masters.”
Second, the process of domesticating wild plants inevitably generally leads to a significant reduction in genetic diversity. Humans select only a small subset of the total genetic diversity of wild species and then continuously select small slivers in successive generations. , which coincides well with the transition to single-stalk, large-eared corn that dominates the landscape of the Midwestern United States. A colleague and I led the Strawberry Breeding Laboratory at the University of California, Davis, examining the genomes of wild and domesticated octoploid strawberries, and found that domesticated strawberries have as many genes as other species. I was surprised to see that there is a diversity of people. wild relatives. This genetic variation has been successfully exploited. The same study showed that the different copies of the gene inherited from four different diploid parental species are all subject to natural selection throughout the history of early and modern domestication strawberries. Each of these parent species provided different genetic fuel reserves to help the species adapt to diverse locations or meet the needs of plant breeders.
A final cross was made between two wild octaploid species. One is native to temperate environments in North America and the other is adapted to the west coasts of North and South America. The resulting hybrids could easily adapt to different environments. A separate study from the University of California, Davis group found that genes selected in cultivated strawberries grown in coastal environments were more likely to be derived from the parent species native to coastal environments, whereas in temperate environments. Genes selected in cultivated strawberries are parent species adapted to temperate ecosystems. By having two genomes from hybridization, strawberries possess exceptional genetic diversity to survive in any environment to which the parent species are adapted.
The evolutionary importance of polyploidy extends well beyond strawberries. The ability to create large amounts of additional genetic material sets the stage for future adaptation to new environments, or the ability to persist in extremely harsh conditions. Sequencing and analysis of dozens of genomes across the tree of life show that although many eukaryotic species now have diploid genome structures, nearly all have signals of ancient polyploidy events. It became clear that there is Organisms have undergone whole-genome duplications and acquired new sets of chromosomes. These events occur prominently before the evolution of major novelties such as vertebrate spines, plant flowers, and yeast fermentation. Genes that are redundantly maintained despite hundreds of millions of years of evolution are important for the development of these traits and provide strong evidence that polyploidy led to the evolution of these new traits. Moreover, polyploidy events appear to occur during mass extinction events such as those at the Cretaceous-Palaeogene boundary about 66 million years ago. Polyploidy may have been important for species survival in this era of large-scale climate change.
The next time you eat strawberries, remember that they are more than just a delicious snack. This is a window into unique genetic and evolutionary processes that explain how species can evolve unprecedented features and survive unprecedented environmental change.
This is an opinion and analysis article and the views expressed by the author or authors are not necessarily Scientific American.
