Abstract
Triplet repeat expansions underlie several human genetic diseases such as Huntington's disease and Friedreich's ataxia. Although such mutations are primarily known from humans, a triplet expansion associated genetic defect has also been reported at the IIL1 locus in the Bur-0 accession of the model plant Arabidopsis thaliana. The IIL1 triplet expansion is an example of cryptic genetic variation as its phenotypic effects are seen only under genetic or environmental perturbation, with high temperatures resulting in a growth defect. Here we demonstrate that the IIL1 triplet expansion associated growth defect is not a general stress response and is specific to particular environmental perturbations. We also confirm and map genetic modifiers that suppress the effect of IIL1 triplet repeat expansion. By collecting and analyzing accessions from the island of Ireland, we recover the repeat expansion in wild populations suggesting that the repeat expansion has persisted at least 60 years in Ireland. Through genome-wide genotyping, we show that the repeat expansion is present in diverse Irish populations. Our findings indicate that even deleterious alleles can persist in populations if their effect is conditional. Our study demonstrates that analysis of groups of wild populations is a powerful tool for understanding the dynamics of cryptic genetic variation.
Highlights
Allelic differences in simple polynucleotide repeats are associated with phenotypic variation in several species (Verstrepen et al, 2005; Levdansky et al, 2007; Michael et al, 2007; Vinces et al, 2009)
We demonstrate that genetic modifiers can mask the iil phenotype and present Quantitative Trait Locus (QTL) mapping for one of these modifiers
We have shown that plants grown at 23◦C have a propensity to display the iil phenotype associated with the repeat expansion when exposed to UV-B
Summary
Allelic differences in simple polynucleotide repeats are associated with phenotypic variation in several species (Verstrepen et al, 2005; Levdansky et al, 2007; Michael et al, 2007; Vinces et al, 2009) In extreme cases, this variation can lead to genetic diseases, as exemplified by the triplet expansion diseases in humans. There is considerable interest in the analysis of cryptic genetic variation, as it can represent either adaptive potential or a source of deleterious alleles that require constant suppression Such hidden genetic substrates could become important upon a change in the environment and may play a critical role in shaping evolution (Gibson and Dworkin, 2004; Ledon-Rettig et al, 2014; Paaby and Rockman, 2014). The strong deleterious nature of the IIL1 triplet repeat expansion is consistent with our previous findings that the GAA/TTC triplet repeat expansion is rare, and may be unique to Bur-0
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