Data from: Magnitude and sign epistasis among deleterious mutations in a positive-sense plant RNA virus

How epistatic interactions between mutations determine the genetic
architecture of fitness is of central importance in evolution. The study
of epistasis is particularly interesting for RNA viruses because of their
genomic compactness, lack of genetic redundancy, and apparent low
complexity. Moreover, interactions between mutations in viral genomes
determine traits such as resistance to antiviral drugs, virulence and host
range. In this study we generated 53 Tobacco etch potyvirus genotypes
carrying pairs of single-nucleotide substitutions and measured their
separated and combined deleterious fitness effects. We found that up to
38% of pairs had significant epistasis for fitness, including both
positive and negative deviations from the null hypothesis of
multiplicative effects. Interestingly, the sign of epistasis was
correlated with viral protein–protein interactions in a model network,
being predominantly positive between linked pairs of proteins and negative
between unlinked ones. Furthermore, 55% of significant interactions were
cases of reciprocal sign epistasis (RSE), indicating that adaptive
landscapes for RNA viruses maybe highly rugged. Finally, we found that the
magnitude of epistasis correlated negatively with the average effect of
mutations. Overall, our results are in good agreement to those previously
reported for other viruses and further consolidate the view that positive
epistasis is the norm for small and compact genomes that lack genetic
robustness.