In corn, however, Hollick's lab had discovered previously that the absence of Pol IV creates clear problems in the plants, such as growing seeds in the tassel.
Hollick and colleagues observed that plants deficient in Pol IV also showed pigmentation in kernels of ears expected not to make any color at all meaning they were expected to be yellow.
"Since we knew the misplaced tassel-seed trait was due to misexpression of a gene, we hypothesized that this pigment trait might be due to a pigment regulator being expressed in a tissue where it normally is never expressed. Molecular analysis showed that that was in fact the case," Hollick said.
The researchers selected dark kernels and light kernels from multiple generations of plants and crossed the plants derived form these different kernel classes to create additional new generations of corn.
"We found that the ears developed from those plants had even more darkly colored kernels and fewer lightly colored kernels. We could segregate the extreme types and cross them together and get this continued intensification of the pigmentation over many generations," he said. "We generated more progeny that had increasing amounts of pigment. This is taking a gene that is genetically null, that doesn't have any function in this part of the plant, and turning it from a complete null to a completely dominant form that produces full coloration.
"Essentially we were breeding a novel trait, but not by selecting for any particular gene. We were just continually altering the epigenetic status of one of the two parental genomes every time."
This led the scientists to question why the affected alleles of the pigmentation gene would behave in this way. An investigation of the affected alleles revealed the nearby presence of a transposon, or transposable element: a tiny piece of DNA that has leapt from one area of the genome to another.
|Contact: Jay Hollick|
Ohio State University