“There were 50 million data points, but we whittled it down to the most important ones,” said Barber.

They found that differences are due mainly to hybrids inheriting distinct small interfering RNAs (siRNAs), a subset of sRNAs, from each parent. The siRNAs interfere with gene expression. They also found that hybridization does not create new siRNAs, but hybrids have a more complex siRNA population than their parents because they inherit distinct siRNAs from both parents.

Moreover, the differences in parental siRNAs originated primarily from repeats, which are the result of retrotransposon activity. Retrotransposons are elements that move around and amplify themselves within a genome.

“This is a new source of genetic diversity that people had overlooked,” said Barber.

“We are not saying that genes are not important,” said Moose. “”But probably the way corn properties are altered in the hybrid situation is mediated by the small RNAs in addition to the genes.”

Moose and Barber hope that their work might provide more insight into how to decide which inbred maize lines to cross. “We don’t want to alter how the plant grows, but if we can tweak it to do whatever it already does either faster or more, that could be an advantage,” said Moose.

The article describing this work, “Repeat Associated Small RNAs Vary Among Parents and Following Hybridization in Maize” by Wesley T. Barber, WeiZhang, Hlaing Win, Kranthi K. Varala, Jane E. Dorweiler, Matthew E. Hudson, and Stephen P. Moose was published in the June 26, 2012, issue of Proceedings of the National Academy of Science.