Evolutionary dynamics of stress-activated mobile elements in Mimulus guttatus
Author: Lauren Hamm
Affiliation: University of California, Berkeley
Keywords: Comparative genomics & genome evolution
To effectively cope with projected warmer and drier growing seasons, plant populations must rapidly adapt to novel conditions through phenotypic evolution or acclimate to environmental shifts through phenotypic plasticity. Adaptation across generations requires populations to acquire heritable genetic variation over short timescales. Although most studies have focused on base pair changes (i.e. single nucleotide polymorphisms), their mutation rates are relatively low compared to transposable elements (TEs), which may self-replicate and generate new insertion variants across the genome in relatively rapid bursts. These TE proliferation events may even be spurred by stress-activated epigenetic derepression, further increasing their potential value as sources of new genetic variation for phenotypic adaptation to worsening climate extremes and oscillations. One expression of these ideas, the “TE-Thrust hypothesis”, predicts that eukaryotic lineages which tolerate short term decreases in fitness brought on deleterious TE insertions may also experience beneficial insertions that fuel adaptive evolution during periods of stress, but whether this mechanism bears out in nature has not been well studied. My research will focus on testing this hypothesis in the common monkeyflower, Mimulus guttatus, a widespread wildflower species that has adapted to thrive in diverse habitats across its range. Expanding empirical and computational methods we recently applied to discover environment-associated genetic variants in one part of the range (Colicchio & Hamm et al. 2021) to a broader survey and by examining TE expression in response to drought and heat, we will gain insight into TE family dynamics over space and time, elucidate patterns of stress activation, and identify evidence that natural TE variation mediates genomic plasticity. Determining the prevalence of positive selection on TEs in closely related lineages could shed light on the potentially conserved capacity of plants to domesticate TEs from selfish, nucleic acid parasites into mutualists that promote host fitness and facilitate adaptive evolution.