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Title: Genetic analysis of kernel traits in maize-teosinte introgression populations

Author
item LIU, ZHENGBIN - University Of Missouri
item Garcia, Arturo
item MCMULLEN, MICHAEL - Retired ARS Employee
item Flint-Garcia, Sherry

Submitted to: G3, Genes/Genomes/Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2016
Publication Date: 8/1/2016
Publication URL: http://handle.nal.usda.gov/10113/63060
Citation: Liu, Z., Garcia, A., McMullen, M., Flint Garcia, S.A. 2016. Genetic analysis of kernel traits in maize-teosinte introgression populations. G3, Genes/Genomes/Genetics. 6(8):2523-2530. doi: 10.1534/g3.116.030155/-/DC1.

Interpretive Summary: Most major crop species were domesticated from wild species between 5000 and 10,000 years ago. Humans primarily selected plants that were easier to harvest and had large seed/fruit size, but also selected for seed/fruit attributes such as flavor. In corn (maize), seed weight increased over ten-fold compared to its wild ancestor, teosinte. In addition, seed shape differs between teosinte and maize, with teosinte seeds being round and maize kernels being flat and more rectangular in shape. One question that remains unanswered is whether humans used seed shape traits as a means for selecting larger seeds. In order to understand the relationship between kernel shape and weight, we used image analysis to measure kernel shape traits in a population that contains both maize and teosinte parents, compared these shape traits to kernel weight, and identified regions of the genome that control each of these traits. We found that kernel weight was related to kernel area, perimeter, length, and width which are all length-based traits, but was not related to roundness traits. Similarly, kernel weight and length are controlled by the same chromosomal regions, but roundness traits are controlled by different chromosomal regions. These results suggest that selection for increased seed weight during domestication acted primarily through length-based traits. Our understanding of how these traits are related to each other and the genes that control each trait will allow geneticists and breeders to simplify relationships among seed traits, and effectively select for new and improved lines in the future.

Technical Abstract: Seed traits have been targeted by human selection during the domestication of crop species as a way to increase caloric and nutritional content of food during the transition from hunter-gather to early farming societies. The primary seed trait under selection was likely seed size/weight as it is most directly related to overall grain yield. Additional seed traits involved in seed shape may have also contributed to larger grain. Maize (Zea mays ssp. mays) kernel weight has increased more than ten-fold in the 9000 years since domestication from its wild ancestor, teosinte (Zea mays ssp. parviglumis). In order to study how size and shape affect kernel weight, we analyzed kernel morphometric traits in a set of ten maize-teosinte introgression populations using digital imaging software. We identified QTLs for kernel area and length with moderate allelic effects that co-localize with kernel weight QTLs. Several genomic regions with strong effects during maize domestication were detected and a genetic framework for kernel traits was characterized by complex pleiotropic interactions. Our results both confirm prior reports of kernel domestication loci and identify previously uncharacterized QTLs with a range of allelic effects enabling future research into the genetic basis of these traits.