Food staples are crucial foods that often make up the majority of a population's diet. These can include foods like rice, maize, or tubers such as potatoes, yams, and cassava. The cultivated potato (Solanum tuberosum L.) is thought to be the third most important staple crop, and a new research study has outlined the evolution of the modern potato. This study has shown that after tomato plants became naturally inbred with another potato-like plant around 9 million years ago, the modern potato was born. This ancient event appears to have triggered the evolution of the tuber, the enlarged root that contains nutrients that are found in potatoes, taro, and yams. The work has been reported in Cell.
"Our findings show how a hybridization event between species can spark the evolution of new traits, allowing even more species to emerge," noted corresponding study author Sanwen Huang of the Chinese Academy of Agricultural Sciences. "We've finally solved the mystery of where potatoes came from."
The origin of the potato has been a mystery, because potatoes are so similar to three Chilean species known as Etuberosum, which do not have tubers. Phylogenetic studies have also suggested that potatoes are closer relatives of tomatoes.
To solve the mystery, the researchers assessed the genomes of 450 cultivated potatoes, and 56 wild potatoes. Every species of potato was found to carry a stable mix of DNA from Etuberosum and tomato plants, which indicated an ancient hybridization event had occurred.
Etuberosum and tomatoes also diverged from a common ancestor around 14 million years ago. Although they had been separate species for 5 million years, the plants were still able to inbreed to generate early potato plants with tubers about 9 million years ago.
The tuber genes were identified as well; they come from a combination of parent genes. A gene called SP6A, which starts tuber formation, comes from the tomato parent, while the IT1 gene that controls the growth of tubers underground is from Etuberosum. Both genes are required for tubers to grow.
This hybridization event seems to have coincided with geological movement, when the Andes mountains quickly rose and new habitats were formed. Early potatoes adapted to live in this changing place, and survived harsh winters.
Since tubers enable potatoes to reproduce without pollination or seeds, they were able to quickly spread to new areas, from grassy valleys to alpine meadows in Central and South America.
"Evolving a tuber gave potatoes a huge advantage in harsh environments, fueling an explosion of new species and contributing to the rich diversity of potatoes we see and rely on today," explained Huang.
Sources: Cell Press, Cell