Coding-Sequence Evolution Does Not Explain Divergence in Petal Anthocyanin Pigmentation Between Mimulus luteus Var...

Area of Science:

• Evolutionary Biology
• Plant Genetics
• Molecular Evolution

Background:

• Understanding genetic constraints on developmental evolution is crucial.
• Noncoding genetic changes may be favored over coding changes due to fewer pleiotropic effects.
• The evolution of novel anthocyanin pigmentation in Mimulus luteus var. variegatus provides a model for studying genetic mechanisms of trait evolution.

Purpose of the Study:

• To investigate the role of coding-sequence changes in the recent evolution of anthocyanin pigmentation in Mimulus.
• To determine if MYB5a/NEGAN protein evolution contributed to increased anthocyanin production in M. luteus var. variegatus.
• To differentiate between coding and noncoding contributions to a novel plant trait.

Main Methods:

• Quantitative image analysis of anthocyanin production in tobacco leaves transfected with MYB5a alleles from different Mimulus taxa.
• Replication of initial experiments and spectrophotometry analysis of extracted anthocyanins.
• Investigation of post-transcriptional editing sites in the MYB5a gene.

Main Results:

• Both MYB5a alleles from Mimulus luteus and M. luteus var. variegatus drove robust anthocyanin production.
• Unexpectedly, the allele from the low-anthocyanin M. l. luteus resulted in significantly higher anthocyanin production.
• Two potential post-transcriptional editing sites were discovered in the MYB5a gene sequence.

Conclusions:

• The gain of petal lobe anthocyanin pigmentation in M. luteus var. variegatus resulted solely from noncoding cis-regulatory evolution, not protein-coding changes.
• The MYB5a protein sequence itself did not drive the increase in anthocyanin production.
• The discovery of post-transcriptional editing in nuclear-encoded plant mRNA opens new avenues for research.