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Maize Collection Traces Genetics and Mutations

Sheridan with Maize

William Sheridan’s maize collection is the largest in the world held by a single investigator

“Greenhouse” sounds familiar to most of us today.  But in this case, we’re talking about “Operation Greenhouse,” a 1940s American atomic bomb test program that has a distant link to the corn seed collection of University of North Dakota geneticist and Chester Fritz Distinguished Professor of Biology William “Bill” Sheridan.

“Scientists from the U.S. Department of Agriculture placed seed corn in one of the obsolete ships that were used to test the effects of atomic blasts,” Sheridan said.  “Those were the days when the United States was still conducting tests above water in the Pacific Ocean.  When those

bombs went off, they released an immense amount of radiation.”

Scientists at the California Institute of Technology (Cal Tech) retrieved the seeds, grew them in the field, and discovered mutations resulting from the radiation.

“The Cal Tech researchers were able to identify, isolate, and propagate a little over a thousand independent separate events where chromosomes were broken up, or had pieces broken off the end of a chromosome,” Sheridan said.  Those broken-off pieces got “glued back” onto another chromosome.

“The seeds from Operation Greenhouse are maintained at the Maize Genetics Stock Center at the University of Illinois, where I got my Ph.D.,” he said.  “They have about 800 of these translocation stocks there.  I’ve received about 450 of those, I’ve grown them, and I have them in this collection.

“There are many uses for these corn specimens and their offspring,” Sheridan said.  “One use that has caught the attention of researchers is that they can be used to produce plants that have two complete sets of all the genes, plus a third set for two regions.  We find that in some cases these plants don’t have a normal appearance; their morphology has changed.”

Down syndrome can help explain what’s going on, Sheridan said.

This syndrome is the result in humans of an egg having an extra chromosome 21.  When it gets fertilized, this will produce an individual who has the extra chromosome 21.  The presence of that extra set of genes somehow causes the nervous system to develop abnormally.  Mental capacity is reduced, and you have certain physical characteristics of Down syndrome, Sheridan explained.

“It’s a puzzle as to why things happen this way when it seems to be simply the result of the presence of an extra copy of this set of genes that is on chromosome 21,” Sheridan said.  “When corn plants have an extra copy, in two regions — part of this chromosome and part of that chromosome — we see characteristic alterations in about 30 percent of them.

“We’d like to find out what’s going on and whether these genes are talking to each other and how they’re interacting,” Sheridan said.  “And so this communication among genes is a major part of our research.”

Sheridan is widely published and well-known in maize genetics circles for his massive and meticulously documented collection of full ears of corn — today numbering about 80,000 — that he has been producing since 1980.  The collection is stored in thousands of hand-made drawers that are stacked row upon row on shelves in a clean, temperature-controlled room in Chandler Hall, one of UND’s oldest buildings.

“This is the largest collection I know of in the world of maize genetic stocks that’s held by any individual investigator,” said Sheridan.  “I have two students working with me — a graduate student and an undergraduate student — doing molecular biology work that relates to genetic research. We’re also doing molecular biology, molecular genetics research, as well as cytogenetics research.”

The tagged ears of corn in this massive scientific collection come from several places, among them the greenhouse on the roof of Starcher Hall, test plots that Sheridan operates in the vicinity of Grand Forks, and test plots that he’s been operating every winter since 1984 on the island of Molokai in Hawaii.

“We have all these wonderful resources, including this collection, here at UND,” Sheridan said.  “I have greatly enjoyed these resources.  At most every place else, researchers have to shell the kernels off the ear because storing whole ears of corn takes up a lot more space.  However, I’m the only maize geneticist on campus, so I’m not sure what will happen to this collection when I pass on.”

Juan Pedraza | Staff Writer