Skip Navigation



MBE Advance Access published online on September 6, 2007
Molecular Biology and Evolution, doi:10.1093/molbev/msm184
This Article
Right arrow Advance Access manuscript (PDF)
Right arrow Supplementary Material
Right arrow All Versions of this Article:
24/11/2412    most recent
msm184v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrowRequest Permissions
Google Scholar
Right arrow Articles by Johnson, D. A.
Right arrow Articles by Thomas, M. A.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Johnson, D. A.
Right arrow Articles by Thomas, M. A.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?

© The Author 2007. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Research Article

The Monosaccharide Transporter Gene Family in Arabidopsis and Rice: A History of Duplications, Adaptive Evolution and Functional Divergence

Deborah A. Johnson1 and Michael A. Thomas

Department of Biological Sciences, Idaho State University, Pocatello, ID

1 Corresponding Author, Dept. of Biological Sciences, Campus Box 8007, Idaho State University, Pocatello, ID 83209-8007, johndeb2{at}isu.edu

Received for publication May 16, 2007. Revision received August 9, 2007. Accepted for publication August 13, 2007.

Current hypotheses of gene duplicate divergence propose that surviving members of a gene duplicate pair may evolve, under conditions of purifying or nearly neutral selection, in one of two ways: With new function arising in one duplicate while the other retains original function (neofunctionalization) or partitioning of the original function between the two paralogs (subfunctionalization). More recent studies propose that subfunctionalization followed by neofunctionalization (subneofunctionalization) explains the divergence of many duplicate genes. In this analysis, we evaluate these hypotheses in the context of the large monosaccharide transporter (MST) gene families in Arabidopsis and rice. MSTs have an ancient origin, predating plants, and have evolved in the seed plant lineage to comprise seven subfamilies. In Arabidopsis, 53 putative MST genes have been identified, with one subfamily greatly expanded by tandem gene duplications. We searched the rice genome for members of the MST gene family and compared them to the MST gene family in Arabidopsis to determine subfamily expansion patterns and estimate gene duplicate divergence times. We tested hypotheses of gene duplicate divergence in 24 paralog pairs by comparing protein sequence divergence rates, estimating positive selection on codon sites, and analyzing tissue expression patterns. Results reveal the MST gene family to be significantly larger (65) in rice with two subfamilies greatly expanded by tandem duplications. Gene duplicate divergence time estimates indicate that early diversification of most subfamilies occurred in the Proterozoic (2500-540 MY) and that expansion of large subfamilies continued through the Cenozoic (65-0 MY). Two thirds of paralog pairs show statistically symmetric rates of sequence evolution, most consistent with the subfunctionalization model, with half of those showing evidence for positive selection in one or both genes. Among eight paralog pairs showing asymmetric divergence rates, most consistent with the neofunctionalization model, nearly half show evidence of positive selection. Positive selection does not appear in any duplicate pairs younger than ~34 MY. Our data suggest that the neofunctionalization, subfunctionalization and subneofunctionalization models describe different outcomes along a continuum of divergence resulting from initial conditions of relaxed constraint after duplication.

Key Words: Gene duplicate divergence • molecular clock • adaptive evolution • monosaccharide transporter • Arabdiopsis thaliana • Oryza sativa


Add to CiteULike CiteULike   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us    What's this?




Disclaimer:
Please note that abstracts for content published before 1996 were created through digital scanning and may therefore not exactly replicate the text of the original print issues. All efforts have been made to ensure accuracy, but the Publisher will not be held responsible for any remaining inaccuracies. If you require any further clarification, please contact our Customer Services Department.