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United States Department of Agriculture

Agricultural Research Service

Title: Est Projects for the Study of Genome Evolution in Legumes

Authors
item Schlueter, Jessica - ISU
item Dixon, Philip - ISU
item Shoemaker, Randy

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: July 1, 2004
Publication Date: N/A

Interpretive Summary: The chromosomal material of most higher organisms has undergone at least one round of duplication in past times. Oftentimes the duplicated genes found on these chromosomes continue to express themselves by producing molecular messages that may be decoded. The difference between the codes of the genes is an estimate of how long ago they duplicated. A study of the differences in the code of duplicated genes can tell us much about the evolutionary history of organisms. In this study the authors analyzed thousands of gene messages to identify potential 'pairs' of duplicated genes. They then estimated the time at which the genes duplicated and found for soybean and barrell medic that at least two rounds of duplication have probably occurred for each. They also found that duplicated genes probably undergo rapid divergence soon after duplication. These studies demonstrate that resources developed from high-throughput genomic projects can have broad implication in answering questions about plant evolution. This information will be of value to geneticists and biologists who wish to compare the biochemistry of related organisms.

Technical Abstract: An analysis of extensive collections of expressed sequence tags (ESTs) of soybean (Glycine max) and barrell medic (Medicago truncatula) identified numerous instances of apparent gene duplications. The distributions of genetic distances within each species were analyzed to identify potential mixtures of normal distributions. In both species more than one normal distribution was identified, suggesting more than one round of genome duplication. Comparisons of the average genetic distance between duplicated genes under each normal distribution, based upon synonymous sequences, provided an estimate of the coalescence times of the apparent duplications. Genome duplication events were estimated to have occurred in soybean at 14.5 MYA and 41.6 MYA. Major duplication events in barrell medic were estimated to have occurred at 20.2 MYA and 54.6 MYA. An analysis of in silico data suggested that some anciently duplicated genes retained similar gene expression patterns while some recently duplicated genes had already diverged in expression patterns. This data suggests that duplicated genes undergo a period of relaxed selection immediately upon duplication and that the duplicates surviving this period remain relatively stable afterwards.

Last Modified: 7/22/2014