Triplet repeats and phenotypic variation in Arabidopsis thaliana

Polymorphisms in microsatellites have been linked to phenotypic diversity in several prokaryotic and eukaryotic organisms. Expansions in triplet repeats underlie several neurodegenerative disorders in humans. We are using Arabidopsis as a model to investigate phenotypic variation conferred by repeats and its natural genetic modification. The Arabidopsis Bur-0 strain harbours a triplet expansion in the IILJ gene, which confers a cryptic growth arrest phenotype. In crosses with Col-O this phenotype do not segregate as a monogenic trait suggesting the presence of modifiers. In the initial chapter, using the Bur-0/Col-0 mapping populations, we have uncovered the genetic architecture of this modifier. In the next chapter of the thesis, we have also tried to understand the role of methylation in the modulating the instability of the repeats in Arabidopsis by using a chemical demethylation compound and by analysing the expression of genes that play a pivotal role in establishment and maintenance of the three different types of methylation. Although the IILJ repeat variability is seen in the intron, in the final chapter, we have explored the variation in the exonic repeats by screening for genes that contain the repeats, which also are predicted to be polymorphic. We have identified some interesting genes and have initiated investigations on the phenotypic consequences of repeat variability in these genes. Identifying modifiers for such deleterious phenotypes and identifying other genes that have repeat variability in Arabidopsis that have striking functional resemblance to human disorders are quintessential to be able to undertake an in depth study the features and aspects pertaining to the understudied and unestablished mechanisms leading to triplet repeat disorders and in the future might pave ways to develop potential therapeutical targets and methods.