Faster growth, darker leaves, a different way of branching - wild varieties of the plant Arabidopsis thaliana are often substantially different from the laboratory strain of this small mustard plant, a favorite of many plant biologists. Which detailed differences distinguish the genomes of strains from the polar circle or the subtropics, from America, Africa or Asia has been investigated for the first time by research teams from TÃ¼bingen, Germany, and California led by Detlef Weigel from the Max Planck Institute for Developmental Biology. The results were surprising: The extent of the genetic differences far exceeds the expectations for such a streamlined genome, as the scientists write in this weekâ€™s edition of Science magazine.
Arabidopsis plants from different geographical origins differ in many traits (the background shows schematically sequence variation in the DNA of these plants).
To track down the variation in the genome of the different Arabidopsis strains, the researchers compared the genetic material of 19 wild strains with that of the genome of the lab strain, which was sequenced in the year 2000. Using a very elaborate procedure, they examined every one of the roughly 120 million building blocks of the genome. For their molecular sleuthing they used almost one billion specially designed DNA probes. "All together, these probes would have seven times the length of human genome," illustrates Weigel the extent of the project. The data were evaluated with several specially designed statistical methods, including a variant of machine learning.
The result of this painstaking analysis: on average, every 180th DNA building block is variable. And about four percent of the reference genome either looks very different in the wild varieties, or cannot be found at all. Almost every tenth gene was so defective that it could not fulfill its normal function anymore!
Results such as these raise fundamental questions. For one, they