ABSTRACT
Microsatellites are common in most species. While an adaptive role for these highly mutable regions has been considered, little is known concerning their contribution towards phenotypic variation. Here we used populations of the common sunflower (Helianthus annuus) at two latitudes to quantify the effect of microsatellite allele length on phenotype at the level of gene expression. We conducted a common garden experiment with seed collected from sunflower populations in Kansas and Oklahoma followed by an RNA-Seq experiment on 95 individuals. The effect of microsatellite allele length on gene expression was assessed across 3325 microsatellites that could be consistently scored. Our study revealed 479 microsatellites at which allele length significantly correlates with gene expression (significant expression short tandem repeats or eSTRs). Further, when irregular allele sizes not conforming to the motif length were removed from the analysis, the number of eSTRs rose to 2379. The percentage of variation in gene expression explained by eSTRs ranged from 1 – 86% when controlling for population and allele-by-population interaction effects at the 479 eSTRs initially identified. Further, 70.4% of these eSTRs are located in untranslated regions (UTRs). A Gene Ontology (GO) analysis revealed that eSTRs are significantly enriched for GO terms associated with cis- and trans-regulatory processes. These findings suggest that a substantial number of transcribed microsatellites can influence gene expression levels. This result is consistent with the hypothesis that these repetitive elements can serve as engines of adaptation.
