Data from: Coding-sequence evolution does not explain divergence in petal anthocyanin pigmentation between Mimulus luteus var. luteus and M. l. variegatus

Biologists have long been interested in understanding genetic constraints
on the evolution of development. For example, noncoding changes in a gene
might be favored relative to coding changes due to being less constrained
by pleiotropic effects. Here we evaluate the importance of coding-sequence
changes to the recent evolution of a novel anthocyanin pigmentation trait
in the monkeyflower genus Mimulus. The magenta-flowered Mimulus luteus
var. variegatus recently gained petal lobe anthocyanin pigmentation via a
single-locus Mendelian difference from its sister taxon, the
yellow-flowered M. l. luteus. Previous work showed that the differentially
expressed transcription factor gene MYB5a/NEGAN is the single causal gene.
However, it was not clear whether MYB5a coding-sequence evolution (in
addition to the observed patterns of differential expression) might also
have contributed to increased anthocyanin production in M. l. variegatus.
Quantitative image analysis of tobacco leaves, transfected with MYB5a
coding sequence from each taxon, revealed robust anthocyanin production
driven by both alleles. Counter to expectations, significantly higher
anthocyanin production was driven by the allele from the low-anthocyanin
M. l. luteus. Together with previously-published expression studies, this
supports the hypothesis that petal pigment in M. l. variegatus was not
gained by protein-coding changes, but instead solely via non-coding
cis-regulatory evolution. Finally, while constructing the transgenes
needed for this experiment, we unexpectedly discovered two sites in MYB5a
that appear to be post-transcriptionally edited – a phenomenon that has
been rarely reported, and even less often explored, for nuclear-encoded
plant mRNAs.