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Relaxed Selection Among Duplicate Floral Regulatory Genes in Lamiales

  • Jan E. AagaardEmail author
  • John H. Willis
  • Patrick C. Phillips
Article

Abstract

Polyploidization is a prevalent mode of genome diversification within plants. Most gene duplicates arising from polyploidization (paralogs) are typically lost, although a subset may be maintained under selection due to dosage, partitioning of gene function, or acquisition of novel functions. Because they experience selection in the presence of other duplicate loci across the genome, interactions among genes may also play a significant role in the maintenance of paralogs resulting from polyploidization. Previously, we identified duplicates of the genes LFY/FLO and AP3/DEF that directly interact in a floral regulatory pathway and are thought to be the result of ancient polyploidization in the Lamiales (> 50 mya). Although duplicates of MADS box genes including AP3/DEF are common throughout the angiosperm lineage, LFY/FLO duplicates in Lamiales are the first reported outside of tetraploid taxa. In order to explore hypotheses for the joint preservation of these interacting floral regulatory genes including novel LFY/FLO paralogs, here we clone FLO and DEF duplicates from additional Lamiales taxa and apply codon substitution models to test how selection acts on both genes following duplication. We find acceleration in the ratio of nonsynonymous-to-synonymous nucleotide substitutions for one (FLO) or both (DEF) paralogs that appears to be due to relaxed purifying selection as opposed to positive selection and shows a different pattern among functional domains of these genes. Several mechanisms are discussed that might be responsible for preservation of co-orthologs of FLO and DEF in Lamiales, including interactions among the genes of this regulatory pathway.

Keywords

Gene duplication Floral regulatory genes 

Notes

Acknowledgments

This work was supported by an NSF IGERT predoctoral fellowship and NSF dissertation improvement grant (DEB-0105176) to J.E.A., an NSF grant (DEB-0075704) to J.H.W., and an NIH grant to P.C.P. (GM54185).

Supplementary material

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Supplementary material

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Copyright information

© Springer Science+Business Media, Inc. 2006

Authors and Affiliations

  • Jan E. Aagaard
    • 1
    • 3
    Email author
  • John H. Willis
    • 2
  • Patrick C. Phillips
    • 1
  1. 1.Center for Ecology and Evolutionary BiologyUniversity of OregonEugeneUSA
  2. 2.Department of BiologyDuke UniversityDurhamUSA
  3. 3.Department of Genome SciencesUniversity of WashingtonSeattleUSA

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