Why couldn't potatoes exist without tomatoes?
“Rather, it's two plant populations,” explains botanist Dr. Sandra Knapp of the Natural History Museum in London.
“These were the ancestors of the plants we know today as tomatoes (Solanum lycopersicum in Latin) and the plant group Solanum etuberosum, three species of which are found in Chile and the Juan Fernandez Islands,” he adds.
As you may have noticed from their Latin names, these plants were related and had "interbred" with each other.
"The genes had mixed together to create something entirely new that could survive in the cold, dry conditions of the Andes," Dr. Knapp says.
Experts call this "interspecies hybridization." It happens frequently, but sometimes it can have unfortunate consequences.
For example, a mule is the result of mating a male donkey and a female horse.
While mules are successful hybrids valued since ancient times, they are not capable of breeding.
Dr. Knapp emphasizes that "crossing" is occurring more frequently in the plant world – this is how many of our garden plants are obtained.
This can happen naturally or through human intervention, resulting in plants that are a blend of both parents.
“Sometimes they can be sterile, meaning they can't develop into a new population,” Dr. Knapp adds.
However, when the combination of conditions is ideal, the "fruit" of this union can be far beyond expectations.
This is what happened with the potato. The potato was born millions of years ago as a result of a chance "relationship" between two species of the Solanaceae family.
"It's fascinating that something so important in our daily lives as the potato has such an ancient and unusual origin," says Dr. Knapp.
"Tomato is the mother, and etuberosum is the father," says Sanwen Huang, a professor at the Chinese Academy of Agricultural Sciences who led the international study, published in July in the journal Cell.
The starting point was already known.
"The hard, starchy vegetable we see on the market doesn't look much like the red, juicy tomato, but they are very, very similar," says Dr. Knapp, who was involved in the research.
Scientists point out that the leaves and flowers of these two plants are very similar, and even the fruit of the potato plant looks like a small green tomato.
"We've known for a long time that beyond their appearance, potatoes, tomatoes, and etuberosum are closely related," Dr. Knapp says. "What we didn't know was which one was closest to potatoes, because different genes were telling us different stories."
Scientists have been trying for decades to unravel the mystery of the origin of this very popular tuber, but it hasn't been easy because the potato's genetics are unusual.
While many living species, including humans, have 2 copies of chromosomes in each cell, this number is 4 in potatoes.
To resolve this paradox, the research team analyzed more than 120 genomes (all the genes or genetic material found in a cell) from dozens of species, including potato, tomato and etuberosum.
The potato genomes they sequenced showed roughly the same tomato-etuberosum split.
"So the potato's ancestor wasn't one or the other, but both," Dr. Knapp says.
Thus, researchers discovered this "romantic relationship" that took place millions of years ago in the foothills of the South American mountains.
This was a successful merger because, as Dr. Knapp emphasized, "it produced new combinations of genes that would enable this species to survive and thrive in the high-altitude habitat of the Andes."
This is largely because the potato plant—even though its above-ground portion resembles its parents—has something hidden that neither has: tubers.
Having tubers can be likened to having a lunchbox with you at all times; tubers store energy that helps withstand winter, drought, or other adverse conditions.
The scientists discovered something else fascinating: The plant that developed the tubers had done so by winning a "genetic lottery."
Both of her parents had genes vital for being able to form lumps.
Unable to do this on their own, these plants achieved this by combining; together, they triggered a process that allowed underground roots to grow into delicious potatoes.
The Chinese team Dr. Knapp worked with even managed to prove it: "They did a lot of elaborate experiments where they disabled these genes to prove their hypothesis, and without these genes, the lumps didn't form."
So the hybridization that gave rise to the potato was more than just a happy accident; the union created a new organ.
And this organ, the potato, is a symbol of evolutionary success.
Its presence allowed the plant to reproduce without the need for seeds or pollinators.
This was a plant that could adapt to very different altitudes and conditions, and this resulted in an "explosion" in its diversity.
Dr. Knapp points out that even today, there are more than 100 species of wild potatoes from the southwestern United States to Chile and Brazil.
However, this ability to reproduce asexually also harmed the potato.
"To grow potatoes, you plant small patches of potatoes, and if you only plant one type of potato, that means all the potatoes you produce are offshoots of each other," Dr. Knapp says.
Genetic uniformity means that none of the potato plants will have a defense against a new disease, for example.
This explains why scientists conducted this study.
Dr. Knapp says the Chinese team aims to create genetically modified potatoes that can be grown from seed.
By adding new genes from wild species, the team hopes to create strains that are more resilient to environmental challenges.
"Myself and the other evolutionary biologists involved in this study wanted to find out who the potato's closest relative was and why it was so diverse," Dr. Knapp says.
“So we approached the research from different perspectives and asked each other questions from our own perspectives. This made the research very fun,” he adds.
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