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Sept. 5, 2019

Underrated and underground, tuber evolution study earns NSF grant

The United States grew more than a million acres of potatoes in 2017, making the number one vegetable crop in the country a tuber. But potatoes are not the only tubers. Jerusalem artichoke, potato bean and mashua—an important food security crop in the Andes—have been eaten for centuries for their valuable calories and nutrition.

Michigan State University plant scientists Robin Buell and Patrick Edger received a four-year, $2.6 million National Science Foundation, or NSF, grant to study tuber evolution. 

“Tubers, like potatoes and yams, give plants perennial capability, provide energy and dormancy during harsh weather and then sprout an identical plant when conditions are right,” said Buell, University Distinguished Professor and director of the Plant Resilience Institute at MSU. “Annuals, like the tomato, can only produce seeds through sexual reproduction. Then it makes a fleshy fruit, drops the seeds and, depending on the species, hopes an animal eats it to disperse those seeds.”

It turns out that potatoes and tomatoes are what Buell described as close cousins. But even in these related species, one makes a tuber and one does not. The grant, which starts this September, aims to understand why.

“All the mechanical parts to make a tuber are in the tomato, but the wiring is different,” said Buell. “Something happened during evolution, and we want to figure out what that something was by looking at species pairs and asking, ‘What is similar and what is different?’”

“I’m excited to uncover how various genes were rewired from an ancestral set of functions that are now collectively involved in tuber development,” said Edger, an assistant professor in the Department of Horticulture in the MSU College of Agriculture and Natural Resources. “It’s a highly complex trait that has evolved independently multiple times. Our study will focus on ten tuber-forming species that are very distantly related–some share a most recent common ancestor over a 100 million years ago.”

Many root and tuber crops originated in the Andes at high altitudes, adapting to the dry climate and intense UV light by storing energy underground. Tubers are a plant’s response to a harsher environment that makes for less than desirable growing conditions. 

Basing their investigations on studies that show potato tubers are signaled by genes that regulate key development traits such as flowering, the Buell and Edger labs will use cutting-edge genomics tools to unearth the mechanisms of tuber development.

“We are going to use a systems biology approach to compare every gene in the genome of each tuber forming species to the genes in the genomes of non-tuber forming species,” Edger said. “This will reveal candidate genes that have been important in the evolution of tuber development that we will then functionally validate in the lab.”

The grant will support undergraduate researchers as well as outreach activities at MSU’s 4-H Children’s Garden, where the public will learn about these underground wonders and their genetically identical sprouts.

“This project is exciting.” Buell said. “Tubers are ubiquitous and critical for food security but often neglected by researchers, so if we can understand the key events in making a tuber, then the question we can ask next is, ‘How can we make a better tuber?’”

By: Val Osowski