RECURRENT MUTATION AND GENOME EVOLUTION: EXAMPLE OF SUGARY1 AND THE ORIGIN OF SWEET MAIZE

Authors: TRACY, WILLIAM - UNIVERSITY OF WISCONSIN; WHITT, SHERRY - NORTH CAROLINA STATE UNIV; Buckler, Edward - Ed

Submitted to: The Plant Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2006
Publication Date: 7/10/2006
Citation: Tracy, W.F., Whitt, S.R., Buckler Iv, E.S. 2006. Recurrent mutation and genome evolution: example of sugary1 and the origin of sweet maize. The Plant Genome. 1:1-6.

Interpretive Summary: Although scientists can point to the recessive allele of a gene named Sugary 1 (Su1) as the genetic basis of sweet corn, they have long disputed how many independent mutations at Su1 have been selected and fixed over time. While previous studies put the number at two or less, we sequenced the Su1 gene from a large number of sweet maize (corn) accessions and found five independent origins. As such, the multiple origins of this allele provide a clear example of the importance of reinvention in the process of evolution. This stands in sharp contrast to the emphasis previously placed on long range migrations to explain the presence of sweet maize across the Americas. This study has particular import for archeological and biological research, as future studies seek to resolve whether independent mutations or migration plays a more dominant role in evolution.

Technical Abstract: Although the homozygous recessive condition of the Sugary 1 (Su1) gene is responsible for the sweet maize phenotype, scientists have long disputed how many independent mutations at Su1 have been selected and fixed over time. While previous studies put the number at two or less, we sequenced 58 accessions of su1 maize found throughout the Americas and found five independent origins in the history of sweet maize-four of which we identified to the nucleotide level. Three of these events involved single amino acid substitutions found in highly conserved residues within a single cleft of the isoamylase enzyme, suggesting that some altered activity may be retained by these enzymes. The multiple origins of the su1 allele provide a clear example of the importance of reinvention in the process of evolution. This stands in sharp contrast to the emphasis previously placed on long range migrations to explain the presence of sweet maize across the Americas. This study has particular import for archeological and biological research, as future studies seek to resolve whether independent mutations or migration plays a more dominant role in evolution.