When it comes to corn, 1 + 1 = more than 2: The offspring of two inbred strains tend to be superior to both of their parents. Characterizing the gene-level variability that leads to this phenomenon, known as heterosis or hybrid vigor, could boost our ability to custom-tailor crops for specific traits, such as high protein content for human consumption or high glucose content for biomass fuel.
With help from the newly released DNA sequence of the common corn strain B73, University of Minnesota plant biologist Nathan Springer and colleagues from Iowa State University, Roche NimbleGen, and the University of Florida have begun doing just that -- and come up with some surprising findings.
In a study reported in the Nov. 20 issues of Science and PLoS Genetics, the researchers compared the genetic sequence of B73 with that of a second inbred strain, Mo17. They discovered an astonishing abundance of two kinds of structural variations between the pair: differences in the copy number of multiple copies of certain stretches of genetic material, and the presence of large chunks of DNA in one but not the other. In fact, at least 180 genes appearing in B73 aren't found in Mo17, and Springer, an associate professor of plant biology in the College of Biological Sciences, suspects that Mo17 likely has a similar number of genes that B73 lacks.
"The genomes of two corn strains are much more different than we would have thought," Springer said. "What struck us is how many major changes there are between two individuals of the same species."
The researchers think that this diversity, which is almost as great as the difference between humans and chimpanzees, is what's behind the superiority of hybrids. When the genetic material from the two very different parents combines, the offspring end up with more expressed traits than either parent -- the best of both worlds, gene-wise.
The findings are important because corn is important. Domesticated some 10,000 years ago, the crop produces billions of bushels of food, feed, and fuel feedstock each year in the United States alone. If we understand the molecular underpinnings of hybrid vigor, Springer says, we can potentially produce true-breeding lines of corn with specific traits for specific uses. That means better use of land, fertilizer, fuel, and other inputs needed to grow crops, and, ultimately, less environmental impact than might otherwise accrue as we work to meet the needs of a growing population.
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