Fruits of Solanum plants, part of the nightshade family, exhibit remarkable diversity, from large red tomatoes and purple eggplants to the toxic green berries found on potato plants.
An international team of researchers, led by Penn State, has developed an enhanced family tree for this group. This new family tree sheds light on the impressive variety in fruit colours and sizes and provides insights into their evolutionary pathways.
The team found that the size and colour of fruits evolved together and that fruit-eating animals were like not the primary drivers of the fruits’ evolution, as had been previously thought, according to a press release. The study, published in the journal New Phytologist, may also provide insight into breeding agriculturally important plants with more desirable traits, the researchers said.
“There are about 1,300 species in the genus Solanum, making it one of the most diverse plant genera in the world,” said João Vitor Messeder, graduate student in ecology and biology in the Penn State Eberly College of Science and Huck Institutes for the Life Sciences and lead author of the paper. “Since the 1970s and ‘80s, researchers have suggested that birds, bats and other fruit-eating animals have driven the evolution of fruits like those in Solanum. However, the importance of the evolutionary history of the plants has been underestimated or rarely considered when evaluating the diversification of fleshy fruits. To better test this hypothesis, we needed first to produce a more robust phylogeny, or family tree, of this plant group to improve our understanding of the relationships between species.”
Solanum plants produce fruits in a wide range of sizes, colours, and nutritional values, from black and purple to red, green, yellow, and orange. Sizes vary from less than a quarter of an inch to 8 inches (0.5 to 20 cm). Besides agricultural species, some are grown for ornamental flowers, and their fruits are consumed by humans and many animals, including birds, bats, reptiles, primates, and other mammals.
The researchers collected plant samples globally, including wild specimens from Brazil, Peru, and Puerto Rico, and plants from botanical gardens. They sequenced their genes from RNA and used additional samples and public data. They compared 1,786 genes from 247 species to reconstruct the Solanum family tree, covering all 10 major clades and 39 of 47 minor clades within the genus.
“By using thousands of genes shared among species that effectively represented the entire genus, we significantly improved the Solanum family tree, making it the most comprehensive to date,” said Messeder, who conducted the research in the lab of Hong Ma, Huck Chair in Plant Reproductive Development and Evolution and professor of biology at Penn State and a co-corresponding author of the paper. “Recent advances in technology allowed us to use more genes than previous studies, which faced many challenges in resolving relationships between species and clades. This improved tree helps us understand when different fruit colours and sizes originated or how they changed as new plant species came about.”
The researchers added considerable resolution of the smaller branches in the group that includes potatoes and tomatoes, as well as their closely and more distantly related wild species. The insights gained, the researchers said, could support crop improvement programs for these species and other crops in the genus.
“If the closest wild relatives of important agricultural crops have desirable traits, it is possible to breed crops with those species or borrow their genes, for example to improve resistance to temperature or pests or to produce larger fruits or fruits of a certain colour,” Messeder said.
Next, the researchers plan to explore how modern interactions between animals and the fruit they eat may shed light on the evolution of both groups as well as explore the evolution of certain genes relevant to fruit colour and size.
