www.the-scientist.com/2008/2/1/30/1/ -
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Published on: 1/1/2008
Last Visited: 2/28/2008
Since the late 1990s, Lolle, then at Harvard University, had been collaborating with Purdue University's Robert Pruitt, to study how the plant cuticle, or epidermis, does its job of wax production, water regulation, and overall plant protection.
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Lolle and Pruitt bred Arabidopsis plants to have a mutation in each gene associated with regulating organ development and fusion.
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Over the course of their experiments, Pruitt and Lolle saw that some of the hothead mutant plants did not have the associated fused reproductive organs - without flowers or exposed stamen - as did their mutant counterparts, which is a double recessive trait (hth).Instead, these individuals had normal looking flowers and leaves, the signifying morphology of the wild-type plants.
As Lolle and Pruitt ran through the classic Mendelian experiments to test their observations, they were stunned at the results they were seeing: F1 generation mutants, bred from parents homozygous for the hth allele, were displaying wild-type morphology and wild-type alleles.
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"I thought maybe it's not all in the alleles, but I didn't get the full connection until Bob [Pruitt] and I collaborated," and found all the fusion mutants from running the genetic screens on the various mutants, one by one.
Wild-type Thale cress, Arabidopsis thaliana, a member of the Cruciferae (cabbage family).A number of factors make A. thaliana ideal for study: a short generation time (5 weeks); a high seed number per plant (10,000); a small genome (about one-tenth the number of base pairs as wheat); a tendency to self-fertilization (which leads to genetic uniformity and stablity); and a susceptibility to infection by Agrobacterium tumifaciens (which means that the plants can be genetically transformed by plasmids).
In every case the reverted allele matched the wild-type sequence exactly, suggesting that the high rate of reversion they were observing was not from another mutation, such as gene silencing.This also suggested to them that the changes they were observing were somehow regulated by a DNA template.Lolle and Pruitt used PCR and DNA blotting to look for such a template, to no avail.
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Pruitt and Lolle devised the theory of an RNA cache to explain how the plants might revert to their grandparents' allelic frequency.
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In September 2006, Steve Jacobsen's group at the University of California, Los Angeles, published what happened when they tried to reproduce the phenomenon that Lolle and Pruitt had observed.9 They found that the hothead mutants had a strong tendency to outcross, rather than self-fertilize, and that plant populations grown in isolation were stable.
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