Neutral Evolution of the Nonbinding Region of the Anthocyanin Regulatory Gene Ipmyb1 in Ipomoea

Neutral Evolution of the Nonbinding Region of the Anthocyanin Regulatory Gene Ipmyb1 in Ipomoea Plant transcription factors often contain domains that evolve very rapidly. Although it has been suggested that this rapid evolution may contribute substantially to phenotypic differentiation among species, this suggestion has seldom been tested explicitly. We tested the validity of this hypothesis by examining the rapidly evolving non-DNA-binding region of an R2R3-myb transcription factor that regulates anthocyanin expression in flowers of the genus Ipomoea. We first provide evidence that the W locus in Ipomoea purpurea , which determines whether flowers will be pigmented or white, corresponds to a myb gene segregating in southeastern U.S. populations for one functional allele and one nonfunctional allele. While the binding domain exhibits substantial selective constraint, the nonbinding region evolves at an average K a / K s ratio of 0.74. This elevated rate of evolution is due to relaxed constraint rather than to increased levels of positive selection. Despite this relaxed constraint, however, ∼20–25% of the codons, randomly distributed throughout the nonbinding region, are highly constrained, with the remainder evolving neutrally, indicating that the entire region performs important function(s). Our results provide little indication that rapid evolution in this regulatory gene is driven by natural selection or that it is responsible for floral-color differences among Ipomoea species. Footnotes Sequence data from this article have been deposited with the EMBL/GenBank Data Libraries under accession nos. AY986823 , AY986824 , AY986825 , AY986826 , AY986827 , AY986828 , AY986829 , AY986830 , AY986831 , AY986832 , AY986833 , AY986834 , AY986835 , AY986836 , AY986837 , AY986838 , AY986839 , AY986840 , AY986841 , AY986842 , AY986843 , AY986844 , AY986845 , AY986846 , AY986847 , AY986848 , AY986849 , AY986850 , AY986851 , AY986852 , AY986853 , AY986854 , AY986855 , AY986856 , AY986857 , AY986858 , AY986859 , AY986860 , AY986861 , AY986862 , AY986863 , AY986864 , AY986865 , AY986866 , AY986867 , AY986868 , AY986869 , AY986870 , AY986871 , AY986872 , AY986873 , AY986874 , AY986875 , AY986876 , AY986877 , AY986878 , AY986879 , AY986880 , AY986881 , AY986882 , AY986883 , AY986884 , AY986885 , AY986886 , AY986887 , AY986888 , AY986889 , AY986890 , AY986891 , AY986892 , AY986893 , AY986894 , AY986895 , AY986896 , AY986897 , AY986898 . Communicating editor: D. R and Received August 12, 2004. Accepted April 28, 2005. Genetics Society of America http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Genetics Genetics Society of America

Neutral Evolution of the Nonbinding Region of the Anthocyanin Regulatory Gene Ipmyb1 in Ipomoea

Genetics, Volume 170 (4): 1967 – Aug 1, 2005

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Publisher
Genetics Society of America
Copyright
Copyright © 2005 by the Genetics Society of America
ISSN
0016-6731
eISSN
1943-2631
D.O.I.
10.1534/genetics.104.034975
Publisher site
See Article on Publisher Site

Abstract

Plant transcription factors often contain domains that evolve very rapidly. Although it has been suggested that this rapid evolution may contribute substantially to phenotypic differentiation among species, this suggestion has seldom been tested explicitly. We tested the validity of this hypothesis by examining the rapidly evolving non-DNA-binding region of an R2R3-myb transcription factor that regulates anthocyanin expression in flowers of the genus Ipomoea. We first provide evidence that the W locus in Ipomoea purpurea , which determines whether flowers will be pigmented or white, corresponds to a myb gene segregating in southeastern U.S. populations for one functional allele and one nonfunctional allele. While the binding domain exhibits substantial selective constraint, the nonbinding region evolves at an average K a / K s ratio of 0.74. This elevated rate of evolution is due to relaxed constraint rather than to increased levels of positive selection. Despite this relaxed constraint, however, ∼20–25% of the codons, randomly distributed throughout the nonbinding region, are highly constrained, with the remainder evolving neutrally, indicating that the entire region performs important function(s). Our results provide little indication that rapid evolution in this regulatory gene is driven by natural selection or that it is responsible for floral-color differences among Ipomoea species. Footnotes Sequence data from this article have been deposited with the EMBL/GenBank Data Libraries under accession nos. AY986823 , AY986824 , AY986825 , AY986826 , AY986827 , AY986828 , AY986829 , AY986830 , AY986831 , AY986832 , AY986833 , AY986834 , AY986835 , AY986836 , AY986837 , AY986838 , AY986839 , AY986840 , AY986841 , AY986842 , AY986843 , AY986844 , AY986845 , AY986846 , AY986847 , AY986848 , AY986849 , AY986850 , AY986851 , AY986852 , AY986853 , AY986854 , AY986855 , AY986856 , AY986857 , AY986858 , AY986859 , AY986860 , AY986861 , AY986862 , AY986863 , AY986864 , AY986865 , AY986866 , AY986867 , AY986868 , AY986869 , AY986870 , AY986871 , AY986872 , AY986873 , AY986874 , AY986875 , AY986876 , AY986877 , AY986878 , AY986879 , AY986880 , AY986881 , AY986882 , AY986883 , AY986884 , AY986885 , AY986886 , AY986887 , AY986888 , AY986889 , AY986890 , AY986891 , AY986892 , AY986893 , AY986894 , AY986895 , AY986896 , AY986897 , AY986898 . Communicating editor: D. R and Received August 12, 2004. Accepted April 28, 2005. Genetics Society of America

Journal

GeneticsGenetics Society of America

Published: Aug 1, 2005

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