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A-maizing!

Almost a hundred years ago, an Illinois farm worker stumbled across a corn stalk of such absurd “monstrosity” that it was initially suspected to be a new species. A disordered and bulbous jumble of kernels, the corn was in fact the result of the mutation of only a single gene called ramosa1. Scientists have known about the existence of ramosa1 since the 1930s, but were unable to identify the actual gene. The mysterious identity was finally discovered by researchers at Cold Spring Harbor Laboratory, who published their findings in the July 24 online edition of the journal Nature.

Modern-day corn can be traced back over 12,000 years to a wild ancestor, teosinte, that grew in Central Mexico. Several millennia of domestication produced the long, straight rows that we know today, and ramosa1 appears to have been integral to this process. Study leader, Dr. Robert Martienssen comments that, "As corn was being domesticated, farmers selected a larger and larger ear with more and more rows of kernels, based on the activity of genes other than ramosa1. But we suspect that as the ear got larger, it needed special alleles of ramosa1 to prevent the extra rows from forming branches instead of kernels."

It was appropriate that the Cold Spring Harbor lab group should be the ones to unlock the identity of the ramosa1 gene - the corn was cultivated on the same site where Barbara McClintock conducted her famous studies into 'jumping genes.' McClintock won a Nobel Prize in 1983 for her discovery that fragments of DNA called transposons could transpose (or jump) from one position on the chromosome to another. This discovery had a profound effect on modern day genetic science, demonstrating that chromosomes were dynamic, changing structures.

Erik Vollbrecht, lead author on the ramosa1 paper, acknowledged McClintock's lingering influence in modern genetics through the "…use of transposable elements or 'jumping genes' - discovered at Cold Spring Harbor by Barbara McClintock - to 'tag' the ramosa1 gene. That enabled us to isolate the gene and determine its DNA sequence for a variety of other experiments."

Vollbrecht and colleagues' study reveals that plants with greater ramosa1 activity (e.g. familiar corncob) tend to have shorter and fewer branches, whereas plants with less ramosa1 activity (e.g. rice) tend to have longer and more frequent branches.

Learn about the groundbreaking work of Barbara McClintock, on our Internet site DNA from the Beginning, in Concept 32: Some DNA can jump.

POSTED August 15, 2005