MBE Advance Access published online on November 24, 2008
Molecular Biology and Evolution, doi:10.1093/molbev/msn268
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Research Article |
ALTERED TRANS-REGULATORY CONTROL OF GENE EXPRESSION IN MULTIPLE ANTHOCYANIN GENES CONTRIBUTES TO ADAPTIVE FLOWER COLOR EVOLUTION IN MIMULUS AURANTIACUS
a Duke University, Department of Biology, Box 90338, Durham, NC, 27708-0338. Fax: 919-660-7293, Phone: 919-684-2295
b Corresponding author. Email: mstreisf{at}duke.edu
Received for publication July 26, 2008. Revision received September 2, 2008. Revision received October 14, 2008. Revision received November 11, 2008. Accepted for publication November 12, 2008.
A fundamental goal in evolutionary biology is to identify the molecular changes responsible for adaptive evolution. In this study, we describe a genetic analysis to determine whether the molecular changes contributing to adaptive flower color divergence in Mimulus aurantiacus affect gene expression or enzymatic activity. HPLC analysis confirms that flower color differences are caused by the presence versus absence of anthocyanin pigments. Co-segregation analysis and in vitro enzymatic assays rule out mutations that affect enzymatic function in the anthocyanin pathway genes. By contrast, co-segregation of gene expression with flower color suggests that tissue-specific differences in pigment production are caused by the coordinated regulatory control of three anthocyanin pathway genes. We provide evidence indicating that these expression differences are caused by a locus that acts in trans- and explains 45% of the phenotypic variance in flower color. A second locus with sequence similarity to the R2R3 MYB family of transcription factors explains 9% of the variation, but does so in a complex fashion. These results demonstrate one of only two examples where we have clear evidence of both the adaptive nature of a flower color transition and evidence for its genetic basis. In both cases, mutations appear to affect expression of the anthocyanin structural genes. Future studies will allow us to determine whether these differences represent a real bias in favor of mutations that affect gene expression.
Key Words: anthocyanin • flower color • gene expression • genetics of adaptation • Mimulus
Sequence data from this article have been deposited with the EMBL/GenBank Data Libraries under accession nos. EU305679 [GenBank] -EU305689.
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