Duplication of centromeric histone H3 (HTR12) gene in Arabidopsis halleri and lyrata, plant species with multiple centromeric satellite sequences
Akira Kawabe 1*, Shuhei Nasuda 2 and Deborah Charlesworth 1
1 University of Edinburgh
2 Kyoto University
* To whom correspondence should be addressed. E-mail: akira.kawabe{at}ed.ac.uk.
Submitted on July 18, 2006
Revised on September 6, 2006
Accepted on 13 September 2006
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Abstract |
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Arabidopsis halleri and lyrata have three different major centromeric satellite sequences, a unique finding for a diploid Arabidopsis species. Since centromeric histones co-evolve with centromeric satellites, these proteins would be predicted to show signs of selection when new centromere satellites have recently arisen. We isolated centromeric protein genes from A. halleri and lyrata and found that one of them, HTR12 (CENP-A), is duplicated, while CENP-C is not. Phylogenetic analysis indicates that the HTR12 duplication occurred after these species diverged from A. thaliana. Genetic mapping shows that HTR12 copy B has the same genomic location as the A. thaliana gene; the other copy (A, at the other end of the same chromosome) is probably the new copy. To test for selection since the duplication, we surveyed diversity at both HTR12 loci within A. lyrata. Overall, there is no strong evidence for an "evolutionary arms race" causing multiple replacement substitutions. The A. lyrata HTR12B sequences fall into three classes of haplotypes, apparently maintained for a long time, but they encode the same amino acid sequences. In contrast, HTR12A has low diversity, but many variants are amino acid replacements, possibly due to independent selective sweeps within populations of the species.
Key Words:
Arabidopsis, Centromeric histone H3, Gene duplication, HTR12, MacDonald-Kreitman test
