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Too many bases lead to genetic defects

Scientists at the Max Planck Institute for Developmental Biology in Tübingen have discovered a genetic defect in Arabidopsis thaliania, which also causes serious neurodegenerative disorders in humans. In Arabidopsis, the expansion of a specific trinucleotide repeat causes the plants to deteriorate. In humans, the expansion of repeats can lead to serious neuronal disorders such as Huntington’s disease, Friedreich’s ataxia or fragile X syndrome.

The researchers led by Detlef Weigel have accidentally discovered a previously unknown genetic defect in the plant Arabidopsis thaliana: some of the plants deteriorated when kept at higher temperatures in air-conditioned greenhouses. These plants have a genetic defect in a specific region of the genome. The researchers have identified a DNA triplet that is repeated more than 400 times. These triplet repeats prevent the correct transcription of the gene and are only able to generate a handful of functional proteins.

A genetic defect provides insights into the genetic basis of neurodegenerative disorders

The discovery made by the researchers from Tübingen is of particular importance because DNA triplet repeats may also be the cause of some serious genetic diseases in humans. Every year around 5 people in 100,000 contract Huntington’s disease, for which no cure is available. The disease, which is characterised by jerky body movements and the decline in some mental abilities, eventually leads to death. One in 50,000 newborns in Central Europe suffer from Friedreich’s ataxia, another neurodegenerative disease that is characterised by progressive motor disorders and dementia. “With Arabidopsis thaliana, we have found a model organism that enables us to investigate the genetic causes and the generation of serious human genetic diseases,” said Detlef Weigel.

Arabidopsis thaliana plants with (left) and without genetic defect (right): triplet repeats lead to the faulty transcription of the gene and to the generation of just a handful of functional proteins. The plants deteriorate at higher greenhouse temperatures. © Max Planck Institute for Developmental Biology

"Using Arabidopsis, we are able to investigate how the triplet repeats change over generations. This cannot be done in humans due to the long gaps between generations. In plant models, we can look at many generations in a very short period of time, and we can also carry out genetic tests which of course is not possible in people,” said Marco Todesco, one of the lead authors of the study.

The scientists have investigated the genome of the Bur-0 strain of Arabidopsis thaliana, a plant that is found virtually everywhere in the world. The researchers found that the growth of this strain was severely impaired when moved from a culture room heated to 23°C into a culture room heated to 27°C. The researchers found that the IIL1 gene of these plants has a DNA triplet that is repeated more than 400 times. In other plants, the triplet is only repeated 20 times. The IIL1 gene codes for a protein that is essential for the chloroplasts and hence for the survival of the plants. The large number of triplet repeats prevents the correct transcription of the gene and leads to small and lean plants.

Small gene segment repeats are common in many organisms and the consequences are not always negative. Since the variations in the genome lead to phenotypic differences between individuals, the researchers assume that this phenomenon plays a role in the evolution of species. “Such repeats expand easily, but they also disappear again. They are therefore very varied and might contribute to short-term evolutionary changes,” said Detlef Weigel.

Original publication:

Sridevi Sureshkumar, Marco Todesco, Korbinian Schneeberger, Ramya Harilal, Sureshkumar Balasubramanian, Detlef Weigel
A genetic defect caused by a triplet repeat expansion in Arabidopsis thaliana
Science, 20th February 2009, prepublished online 29th January, 2009; doi: 10.1126/science.1164014

Further information:
Prof. Dr. Detlef Weigel
Max Planck Institute for Developmental Biology, Tübingen
Tel.: +49 7071-601-1410
E-mail: Detlef.Weigel(at)tuebingen.mpg.de

Dr. Susanne Diederich
Press and Public Relations
Max Planck Institute for Developmental Biology, Tübingen
Tel.: +49 7071-601-333
E-mail: presse(at)tuebingen.mpg.de

Website address: https://www.biooekonomie-bw.de/en/articles/pm/too-many-bases-lead-to-genetic-defects/