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Molecular and Chromosomal Evidence for Allopolyploidy in Soybean^1,[OA]

Department of Agronomy (N.G., J.G.W., C.H., J.M., S.A.J.) and Interdisciplinary Life Science Program (N.G., S.A.J.), Purdue University, West Lafayette, Indiana 47907; Division of Plant Sciences, Bond Life Science Center, University of Missouri, Columbia, Missouri 65211 (S.F., G.S.); and Department of Plant Biology, Cornell University, Ithaca, New York 14853 (J.D.)

Recent studies have documented that the soybean (Glycine max) genome has undergone two rounds of large-scale genome and/or segmental duplication. To shed light on the timing and nature of these duplication events, we characterized and analyzed two subfamilies of high-copy centromeric satellite repeats, CentGm-1 and CentGm-2, using a combination of computational and molecular cytogenetic approaches. These two subfamilies of satellite repeats mark distinct subsets of soybean centromeres and, in at least one case, a pair of homologs, suggesting their origins from an allopolyploid event. The satellite monomers of each subfamily are arranged in large tandem arrays, and intermingled monomers of the two subfamilies were not detected by fluorescence in situ hybridization on extended DNA fibers nor at the sequence level. This indicates that there has been little recombination and homogenization of satellite DNA between these two sets of centromeres. These satellite repeats are also present in Glycine soja, the proposed wild progenitor of soybean, but could not be detected in any other relatives of soybean examined in this study, suggesting the rapid divergence of the centromeric satellite DNA within the Glycine genus. Together, these observations provide direct evidence, at molecular and chromosomal levels, in support of the hypothesis that the soybean genome has experienced a recent allopolyploidization event.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Scott A. Jackson (sjackson{at}purdue.edu).

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www.plantphysiol.org/cgi/doi/10.1104/pp.109.137935

^* Corresponding author; e-mail sjackson{at}purdue.edu.

Received March 2, 2009; accepted July 9, 2009; published July 15, 2009.