Small Genes Make Big Hybrids

September 16, 2009 07:00 PM

Pam Smith, Farm Journal Seeds & Production Editor

For most of us, hybrid corn provided our early genetics lessons. Every science and biology teacher under the sun hammered into us that the crossing of two defined parent inbred lines resulted in a bigger and stronger offspring. Heterosis—or hybrid vigor—became one truth you could count on.
But why? Why do corn hybrids show superior performance to their parents? That's a question Steve Moose, University of Illinois professor of Maize Functional Genomics wants to answer. "We still don't really understand the genetic basis for how hybrid vigor works,” says Moose. "Answering the question should allow scientists to better predict which parents will make the best hybrids and to further increase corn yields.”
Moose says one of the most exciting biological discoveries made during the past decade has been the importance of small RNAs. Small RNAs are produced in the cells of all higher organisms (including corn and people) and function to turn off other genes. They are divided into two major groups: microRNAs”, that regulate the rate of development and response to environmental stress, and "small-interfering RNAs”, that provide immunity to viral infections or interfere with virus activity.
"This new class of small RNA genes may be key to unlocking the mystery of hybrid vigor,” Moose says. "Because they are small, they are likely to have been overlooked in previous studies that looked for genes influencing heterosis.” New lab techniques are also aiding scientists to more rapidly characterize the small RNAs produced from many of the "founding fathers” of today's commercial corn hybrids. Combining this information with the sequence of the corn genome is unlocking valuable insights.
Illinois graduate student Wes Barber is also working on the project. "So far we've found inbred parents contribute different small RNAs to the hybrid,” Barber says. "We are learning that the small RNAs that control the speed of development and flowering time in corn differ greatly in hybrids compared to inbred parents. We also see a greater amount of small interfering RNA production in hybrids, which could explain their greater stress tolerance.”
The ultimate goal is to improve predictions of which parents will produce the highest heterosis and grain yield. "Our goal is to reduce the amount of effort spent on finding and crossing the best parental lines, which is the most expensive aspect of producing hybrid corn seed,” Barber adds.
This project receives support from the University of Illinois Critical Research Initiative and the National Science Foundation. Corn genome sequencing has been carried out with funds provided by the National Corn Growers Association. Want to really dig deep into functional gene genomics, following this link:

You can email Pam Smith at

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